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Pentacene is an important model organic semiconductor in both the singlet exciton fission (SF) and organic electronics communities. We have investigated the effect of changing crystal structure on the SF process, generating multiple triplet excitons from an initial singlet exciton, and subsequent triplet recombination. Unlike for similar organic semiconductors that have strong SF sensitive to polymorphism, we find almost no quantitative difference between the kinetics of triplet pair (TT) formation in the two dominant polymorphs of pentacene. Both pairwise dimer coupling and momentum-space crystal models predict much faster TT formation from the bright singlet excited state of the Bulk vs ThinFilm polymorph, contrasting with the experiment. GW and Bethe–Salpeter equation calculations, including exciton–phonon coupling, reveal that ultrafast phonon-driven transitions in the ThinFilm polymorph compensate the intrinsically slower purely Coulomb-mediated TT formation channel, rationalizing the similarity in observed rates. Taking into account the influence of subtle structural distinctions on both the direct and phonon-mediated SF pathways reveals a predictive capability to these methods, expected to be applicable to a wide variety of molecular crystals. [ABSTRACT FROM AUTHOR]

Pentacene is one of the most investigated organic semiconductors. It is well known that the motion of excitons in pentacene and other organic semiconductors is determined by inter-molecular exciton coupling based on charge-transfer processes. In the present study, we demonstrate the impact of the admixture of tetracene, which has a larger band gap and interrupts the pentacene–pentacene interaction, on the exciton behavior in pentacene. Using a combination of optical absorption and electron energy-loss spectroscopy, we show that both the Davydov splitting and the exciton band width in pentacene strongly decrease with increasing tetracene concentration, while the decrease of the exciton band width is substantially larger. [ABSTRACT FROM AUTHOR]

A hybrid quantum mechanics/molecular mechanics setup was used to model electronically excited pentacene in the crystal phase. Particularly interesting in the context of singlet fission (SF) is the energetic location of the antiferromagnetically coupled multiexcitonic singlet state, 1(TT), and the ferromagnetically coupled analog in relation to the optically bright singlet state. To provide photophysical properties of the accessible spin manifold, combined density functional theory and multi-reference configuration interaction calculations were performed on pentacene dimers and a trimer, electrostatically embedded in the crystal. The likelihood of a quintet intermediate in the SF process was estimated by computing singlet–quintet electron spin–spin couplings employing the Breit–Pauli Hamiltonian. The performance of the applied methods was assessed on the pentacene monomer. The character of the optically bright state and the energetic location of the 1(TT) state depend strongly on the relative orientation of the pentacene units. In the V-shaped dimers and in the trimer, the optically bright state is dominated by local and charge transfer (CT) excitations, with admixtures of doubly excited configurations. The CT excitations gain weight upon geometry relaxation, thus supporting a CT-mediated SF mechanism as the primary step of the SF process. For the slip-stacked dimer, the energetic order of the bright and the 1(TT) states swaps upon geometry relaxation, indicating strong nonadiabatic coupling close to the Franck–Condon region—a prerequisite for a coherent SF process. The multiexcitonic singlet, triplet, and quintet states are energetically too far apart and their spin–spin couplings are too small to bring about a noteworthy multiplicity mixing. [ABSTRACT FROM AUTHOR]

Singlet fission (SF) is a very significant photophysical phenomenon and possesses potential applications. In this work, we try to give a rather detailed theoretical investigation of the SF process in the stacked polyacene dimer by combining the high-level quantum chemistry calculations and the quantum dynamics simulations based on the tensor network method. Starting with the construction of the linear vibronic coupling model, we explore the pure electronic dynamics and the vibronic dynamics in the SF processes. The role of vibrational modes in nonadiabatic dynamics is addressed. The results show that the super-exchange mechanism mediated by the charge-transfer state is found in both pure electronic dynamics and the nonadiabatic dynamics. Particularly the vibrational modes with the frequencies resonance with the adiabatic energy gap play very import roles in the SF dynamics. This work not only provides a deep and detailed understanding of the SF process but also verifies the efficiency of the tensor network method with the train structure that can serve as the reference dynamics method to explore the dynamics behaviors of complex systems. [ABSTRACT FROM AUTHOR]

Using Bayesian spectroscopy, we performed spectral decomposition of gate modulation (GM) spectra measured in a pentacene organic field-effect transistor to understand comprehensively the optical nonlinear response due to GM and hole injection. Although GM spectra contain a variety of spectral components, by Bayesian spectroscopy, we can specify the role of each component in the nonlinear response by performing model selection that chooses the spectral components needed to explain the data without preconceptions. For a GM spectrum under positive GM, Bayesian spectroscopy shows that nonlinear responses by the change in polarizability dominate the GM spectrum among several types of Stark signals induced by the GM electric field, which is a physically valid conclusion. For GM spectra under negative GM where gate-induced carriers are injected, Bayesian spectroscopy succeeds in completely elucidating the spectral structure, which is composed of the two types of Stark signals due to changes in the polarizability and the dipole moment, bleaching, and gate-induced absorption signals. A pentacene film is known to have solid and isolated molecular phases, which may give different spectral responses. Therefore, we compared a model that treats these responses equally and a model that distinguishes them. Bayesian spectroscopy selects the latter models for all GM spectra, revealing statistically that nonlinear optical effects and hole injection effects are different in these phases. [ABSTRACT FROM AUTHOR]

Boron-doped acenes have attracted attention due to their unique structures and intriguing luminescent properties. However, the hitherto known boron-doped acenes have only one or two boron atoms, limiting the chemical space of this unique family of compounds and the capability to tune their optical properties. Herein, we report the synthesis of quadruply boron-doped acenes, including pentacene, heptacene, and nonacene. The importance of the boron doping level on the luminescent properties of acenes is demonstrated. The title compounds manifest enhanced Lewis acidity as compared with dihydrodiboraacenes, leading to Lewis-base-responsive emission in the solid state. Moreover, quadruply boron-doped nonacene displays mechanochromic luminescence in addition to Lewis-base-responsive properties, realizing high-contrast solid-state multicolor emission. This work greatly expands the chemistry of boron-doped acenes and offers opportunities for developing boron-based luminescent materials. Boron-doped acenes have attracted attention due to their unique structures and luminescent properties but the hitherto known boron-doped acenes have only one or two boron atoms, limiting the chemical space of this family of compounds. Here, the authors demonstrate the synthesis of quadruply boron-doped acenes, including pentacene, heptacene, and nonacene. [ABSTRACT FROM AUTHOR]

Top‐contact bottom‐gate pentacene OFETs are fabricated with single layer dielectrics comprised of either polystyrene (PS), poly(4‐methylstyrene) (P4MS), or poly(4‐tert‐butylstyrene) (P4TBS). The polystyrenes are blended with varying concentrations of two different small molecules, dibenzotetrathiafulvalene (DBTTF) and 2,8‐difluoro‐5,11‐bis(triethylsilylethynyl)anthradithiophene (diF‐TES‐ADT), to form small, separated crystallites contained throughout the polymer dielectric layer. The OFET characteristics of these devices are investigated and their threshold voltage shifts are measured after −70 V static charging for 5 min. Two‐terminal measurements are conducted using multiple different gate biases in the range of −50 to +50 V to investigate memristor behavior in the devices. OFETs containing DBTTF exhibited ΔVth increases as large as 330% relative to control OFETs containing no DBTTF, while OFETs containing at least 7.5 wt.% DBTTF exhibited memristor activity, with currents ranging from 20 nA to 44 µA depending on the applied bias. This work demonstrates that including small, separated crystallites in polymer dielectrics enhances their charge storage ability and can be promising for creating nonbinary memory devices for data processing. Additionally, the observed memristor activity indicates the OFETs in this work can be used in development of neuromorphic systems that aim to mimic the synaptic behavior of the human nervous system. [ABSTRACT FROM AUTHOR]

Molecular assemblies featuring two-dimensionality have attracted increasing attention, whereas such structures are difficult to construct simply relying on spontaneous molecular assembly. Here, we present two-dimensional assemblies of acene chromophores achieved using a tripodal triptycene supramolecular scaffold, which have been shown to exhibit a strong ability to assemble molecular and polymer motifs two-dimensionally. We designed pentacene and anthracene derivatives sandwiched by two triptycene units. These compounds assemble into expected two-dimensional structures, with the pentacene chromophores having both sufficient overlap to cause singlet fission and space for conformational change to facilitate the dissociation of a triplet pair into free triplets, which is not the case for the anthracene analog. Detailed spectroscopic analysis revealed that the pentacene chromophore in the assembly undergoes singlet fission with a quantum yield of 88 ± 5%, giving rise to triplet pairs, from which free triplets are efficiently generated (FT = 130 ± 8.8%). This demonstrates the utility of the triptycene-based scaffold to design functional p-electronic molecular assemblies. [ABSTRACT FROM AUTHOR]

6,13‐Diethynylpentacene derivatives with sterically bulky substituents (Tr*, tris(3,5‐di‐tert‐butylphenyl)methyl groups) appended to the ethynyl moieties at the 6‐ and 13‐positions have been synthesized, as well as derivatives with electron‐withdrawing fluorine groups on the 1,2,3,4,8,9,10,11‐positions. These molecules are designed to investigate relationships between steric and electronic effects on the stability of pentacene toward endoperoxide formation via reaction with photosensitized oxygen in solution under ambient light (i. e., ‘laboratory’ conditions). It is evident from the study that stabilization through changes to the electronic characteristics of pentacene are more effective than the incorporation of sterically bulky groups at the acetylenic termini. Selected pentacene derivatives have been made into binary, amorphous films with the fullerene derivative PCBM to investigate the stability imparted by substituents against cycloaddition reactions. Overall, the introduction of steric protection through the incorporation of Tr* groups is not an efficient strategy for enhancing the persistence of pentacenes. Stabilization through fluorination proves successful for extending the lifetime of the pentacene derivatives by an order of magnitude in solution. Notably, the persistence of pentacene derivatives in solution can also be enhanced through the use of ethereal solvents stabilized with butylated hydroxy toluene (BHT) and/or an increased number of trialkylsilyl groups as substituents. [ABSTRACT FROM AUTHOR]

A selective deelectronation reagent with very high potential of +2.00 (solution)/+2.41 V (solid‐state) vs. Fc+/0 and based on a room temperature stable perfluoronaphthalene (naphthaleneF) radical cation salt was developed and applied. The solid‐state deelectronation of commercial naphthaleneF with [NO]+[F{Al(ORF)3}2]− generates [naphthaleneF]+⋅[F{Al(ORF)3}2]− (ORF=OC(CF3)3) in gram scale. Thermochemical analysis unravels the solid‐state deelectronation potential of the starting [NO]+‐reagent to be +2.34 V vs. Fc+/0 with [F{Al(ORF)3}2]− counterion, but only +1.14 V vs. Fc+/0 with the small [SbF6]− ion. Selective reactions demonstrate the selectivity of [naphthaleneF]+⋅ for deelectronation of a multitude of organ(ometall)ic molecules and elements in solution: providing the molecular structures of the acene dications [tetracene]2+, [pentacene]2+ or spectroscopic evidence for the carbonyl complex of the ferrocene dication [Fc(CO)]2+, the [P9]+ cation from white phosphorus, the solvent‐free copper(I) salt starting from copper metal and the dicationic Fe(IV)‐scorpionate complex [Fe(sc)2]2+. [ABSTRACT FROM AUTHOR]

Transistors find application within various integrated circuits (ICs) alongside a multitude of electronic devices. These ICs have become integral components in contemporary systems. When organic semiconducting materials constitute the active layer, transistors are termed "organic transistors." The enhancement of diverse device characteristics is achievable through the modeling and simulation of these organic transistors. This study focuses on the simulation of different configurations of pentacene-based organic transistors. To augment device performance, an active layer comprising pentacene is coupled with 5 and 15 nm graphene. Notably, the top gate configuration yields an increase in ON/OFF ratio from 102 to 107, accompanied by an enhancement in sub-threshold swing from 276 to 59 mV/decade. Similarly, the bottom gate configuration exhibits an ON/OFF ratio improvement from 105 to 109, alongside a sub-threshold swing enhancement from 108 to 59 mV/decade. Leveraging graphene as the active layer material results in substantial benefits. These encompass a heightened on-current of 210 mA, a reduced sub-threshold swing of 58 mV/decade, and a significantly enhanced ON/OFF ratio of 1017. [ABSTRACT FROM AUTHOR]

Transfer integral is a crucial parameter that determines the charge mobility of organic semiconductors, and it is very sensitive to molecular packing motifs. The quantum chemical calculation of transfer integrals for all the molecular pairs in organic materials is usually an unaffordable task; fortunately, it can be accelerated by the data-driven machine learning method now. In this work, we develop machine learning models based on artificial neutral networks to predict transfer integrals accurately and efficiently for four typical organic semiconductor molecules: quadruple thiophene (QT), pentacene, rubrene, and dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT). We test various forms of features and labels and evaluate the accuracy of different models. With the implementation of a data augmentation scheme, we have achieved a very high accuracy with the determination coefficient of 0.97 and mean absolute error of 4.5 meV for QT, and similar accuracy for the other three molecules. We apply these models to studying charge transport in organic crystals with dynamic disorders at 300 K and obtain the charge mobility and anisotropy in perfect agreement with the brutal force quantum chemical calculation. If more molecular packings representing the amorphous phase of organic solids are supplemented to the dataset, the current models can be refined to study charge transport in organic thin films with polymorphs and static disorders. [ABSTRACT FROM AUTHOR]

Distinct from inorganic 2D nanomaterials (e.g., graphene, MoS2, etc,), self‐assembled organic 2D materials are significant due to the unique advantages of fine structure tunability and functionality. Electronically and photofunctionally‐active compounds (e.g., pentacene, p‐sexiphenyl) are highly attractive for applications but are limited by difficult handling and the existence of only a few native structures of the compounds. Here, it is shown that a p‐sexiphenyl derivative incorporated into 2D multilamellar sheets with chromophores oriented in the layers exhibits a significant polarization of photoluminescence. Highly emissive, amphiphilic sexiphenyl with hydrophilic/hydrophobic groups self‐assembles at air–water interface with chromophore orientation in the resulting films being controlled by monolayer compression. Large‐area multilamellar structures with p‐sexiphenyl chromophores highly oriented against the 2D plane are prepared by consecutive film transfers. The 2D sheets exhibit significant polarization of photoluminescence with polarization ratio 0.8 between orthogonal in‐plane axes. Notably, multilamellar structures cannot be established for the same p‐sexiphenyl using thermotropic processing thus emphasizing the importance of the 2D sheet multilayer synthesis process. Amphiphile design can be applied for the tailored synthesis of large‐area multilayered 2D sheets and used to construct highly efficient light‐emitting devices. [ABSTRACT FROM AUTHOR]

2,9‐ and 2,10‐diphenylpentacene were synthesized by direct C−H borylation of ketal‐protected pentacene, followed by halodeboronation, resolution of the dihalo isomers, Suzuki arylation, cleavage of the ketals and decarbonylation in the solid state. They were studied as main active components in organic field effect transistors (OFETs). Diphenyl substitution of pentacene affects the unit cell dimensions only slightly, preserving a face to edge molecular packing in the first layers of thin films evaporated on SiO2 substrates. Both isomers self‐assemble into nanoribbons during the thin film growth upon vapor deposition. The similarity between the surface induced phases of the 2,9‐isomer and unsubstituted pentacene leads to similar 4‐probe hole mobilities, i. e. 0.13 cm2 V−1 s−1 for the former. Whereas 2,9‐disubstitution thus does essentially preserve the thin film characteristics of unsubstituted pentacene, 2,10‐disubstitution is detrimental to the molecular ordering in the thin films and therefore to the field effect mobility which is only 0.07 cm2 V−1 s−1. The known strong enhancement of field effect mobility observed upon diphenyl substitution of anthracene can thus not be emulated analogously with pentacene. [ABSTRACT FROM AUTHOR]

Combination band and overtone transitions of polycyclic aromatic hydrocarbon (PAH) cations in the 2000–2900 cm-1 (5-3.5 µm) region are implicated as carriers of the 'quasi-continuum' observed in the near-infrared (IR) emission spectra of many astronomical objects. In neutral PAHs, the strongest absorption features are concentrated in the 700–900 cm-1 (14–11 µm) range, which are associated with CH out-of-plane bending motions. Upon ionization, this shifts to the 1000–1600 cm-1 (10–6 µm) range, where bands are associated with C=C stretches and CH in-plane bends. Anharmonicity is required to accurately characterize the IR absorption spectrum of PAHs, indicated herein by the ability to directly assign the bands in high-resolution experimental absorption spectra of neutral and cationic phenanthrene, pyrene, and pentacene. Neutral PAHs are indicated as the source of the strong 3.3 and 11.2 µm astronomical PAH features, while the broad features in the 6–10 µm region and the 'quasi-continuum' from 3.5–5 µm stem from PAH cations. This study reinforces the need for including anharmonicity in the computation of IR absorption and emission spectra of larger and more complex PAHs. This is particularly pertinent to the interpretation of data returned by JWST. [ABSTRACT FROM AUTHOR]

Organic semiconductors are promising candidates for next‐generation photodetectors owing to their unique properties including large absorption coefficient and intrinsic mechanical flexibility. However, limited by high defect density, large exciton binding energy, and short exciton diffusion length, many challenges remain for fabricating high‐performance organic photodetectors, especially for scenarios where weak light sensing and high‐speed imaging are required. Herein, by coupling single‐crystal pentacene with monolayer graphene, a vertical organic phototransistor with excellent zero‐bias photon detecting capacity is demonstrated. Under self‐powered weak light condition, the responsivity and specific detectivity are 2.86 AW−1 and 3.3 × 1011 Jones (based on experiment spectral noise density), respectively. It is demonstrated that weak light down to 25 nWcm−2 can be detected. When operating with an external bias, the responsivity of the device increases dramatically (up to 105 AW−1), and a better 3 dB bandwidth (≈74 kHz) is obtained. Finally, imaging functionality is demonstrated by employing this vertical transistor as a single‐sensing pixel. This work suggests organic single crystals exhibit enormous potential in advanced optoelectronic systems, and may provide a viable route for weak light detecting and high‐speed imaging. [ABSTRACT FROM AUTHOR]

We report soluble tetrakis‐biphenylyl substituted pentacenes comprised of sp2 carbons and synthesized from pentacene‐5,7,12,14‐tetraone. Intramolecular Yamamoto coupling of two tetrakis(chlorobiphenylyl)pentacenes yields helical, doubly wrapped pentacenes, in which the quaterphenylene units solubilize the pentacenes and shield their central anthracene units to an unprecedented degree. The criss‐cross‐bridged pentacenes resist (photo)oxidation, Diels–Alder reactions and are much less reactive than TIPS‐ethynylated pentacene. Extension of this concept might provide access to the larger acenes. [ABSTRACT FROM AUTHOR]

Inspired by the collective behaviors of active systems in nature, the collective behavior of micromotors has attracted more and more attention in recent years. However, little attention has been paid to the collective behavior of the immobilized micromotor, i.e., the micropump. In this paper, a unique pentacene-based micropump is reported, which demonstrates dynamic collective behavior activated by white light irradiation. The light irradiation may generate the photochemical reactions between pentacene and water, leading to the electroosmotic flow. As a result, this micropump is capable of pumping the surrounding solution inward along the substrate surface based on the electroosmosis mechanism. Intriguingly, the inward pumping causes the agglomeration of the tracer particles on the surface of the micropump. In addition, the aggregation can migrate following the change in the light irradiation position between two adjacent micropumps. Based on the aggregating and migrating behaviors of this pentacene-based micropump, we have achieved the conductivity restoration of the cracked circuit. [ABSTRACT FROM AUTHOR]

Co-deposited molecular heterostructures with statistical intermixing of the constituents are attractive candidates to tune the optical and the transport properties, as well as the ability to promote photophysical processes like singlet fission. In order to comprehend and control the singlet fission mechanism in these systems, it is of utmost interest to study the underlying excited state dynamics. In this work, thin films of anthradithiophene blended with the efficient singlet fission material pentacene are investigated by means of time-resolved and temperature-dependent photoluminescence spectroscopy with a time resolution of a few picoseconds. The analysis of the photoluminescence dynamics points toward efficient funneling of excitons from anthradithiophene via isolated pentacene molecules to agglomerates of pentacene, where eventually singlet fission occurs. The efficient and largely temperature-independent quenching of the luminescence in anthradithiophene is attributed to a favorable cascade-like alignment of the energy levels, and it is hypothesized that Förster resonance energy transfer is the main driving mechanism for exciton transport to pentacene agglomerates. The system investigated here can serve as a blueprint for the design of other molecular heterostructures with spatially separated light harvesting and singlet fission regions. [ABSTRACT FROM AUTHOR]

We report the local surface potential mapping of pentacene film prepared by physical vapor deposition with scanning kelvin probe microscopy where the sample is scanned under different gate voltages. Surface topography and the corresponding potential maps were obtained simultaneously. Spatial distribution of the surface potential at a low gate voltage is clearly correlated with topographic features. A lower electrostatic potential was measured at the grain boundaries (GBs), suggesting that GBs behave as hole traps. This observation is bolstered by conductive atomic force microscopy (C‐AFM) data, which reveals a higher conductivity within the grains as opposed to the GBs. An increase in gate voltage minimizes the potential differences at the grain and GBs, suggesting a modification in trap occupancy. We expect that these experimental results, along with existing theories, will provide a better understanding of the microstructural‐electrical properties of pentacene film. Research Highlights: Local surface potential mapping of pentacene film with scanning kelvin probe microscopy.Correlation between the surface potential map and topography at a low gate voltage.Decrease of the potential distribution inhomogeneity by the gate voltage increasement.Higher conductivity at inner grain than grain boundary in conductive atomic force microscopy. [ABSTRACT FROM AUTHOR]

Organic field‐effect transistors (OFETs) hold great promise for applications in non‐volatile memories, detectors, and artificial synapses due to the good flexibility and biocompatibility. However, certain drawbacks such as high operating voltages and significant degradation in endurance characteristics have hindered their practical implementations. Herein, a novel approach is proposed to enhance the performance of OFETs by incorporating a bi‐functional n‐type polymer semiconductor interlayer, Poly‐{[N,N'‐bis(2‐octyldodecyl)naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)} (N2200), into a pentacene OFET structure. The device exhibits remarkable improvements, with reliable P/E operation cycles of over than 104 and a retention time of more than 10 years. On one hand, the inclusion of N2200 as an n‐type semiconductor effectively reduces the height of hole‐injection barrier for trapping and thus reducing the working voltage based on the electrostatic induction theory. On the other hand, n‐type semiconductor N2200 serves as a native hole‐consumption (or hole‐trapping) dielectric, and its narrower bandgap restrains the formation of deep hole‐traps, thus favoring the endurance characteristics of the OFET. [ABSTRACT FROM AUTHOR]

A series of ferrocene(Fc)‐bridged pentacene(Pc)‐dimers [Fc−Ph(2,n)−(Pc)2: n=number of phenylene spacers] were synthesized to examine the tortional motion effect of Fc‐terminated phenylene linkers on strongly coupled quintet multiexciton (5TT) formation through intramolecular singlet fission (ISF). Fc−Ph(2,4)−(Pc)2 has a relatively small electronic coupling and large conformational flexibility according to spectroscopic and theoretical analyses. Fc−Ph(2,4)−(Pc)2 exhibits a high‐yield 5TT together with quantitative singlet TT (1TT) generation through ISF. This demonstrates a much more efficient ISF than those of other less flexible Pc dimers. The activation entropy in 1TT spin conversion of Fc−Ph(2,4)−(Pc)2 is larger than those of the other systems due to the larger conformational flexibility associated with the torsional motion of the linkers. The torsional motion of linkers in 1TT is attributable to weakened metal‐ligand bonding in the Fc due to hybridization of the hole level of Pc to Fc in 1TT unpaired orbitals. [ABSTRACT FROM AUTHOR]

Triplet dynamics in singlet fission depend strongly on the strength of the electronic coupling. Covalent systems in solution offer precise control over such couplings. Nonetheless, efficient free triplet generation remains elusive in most systems, as the intermediate triplet pair 1(T1T1) is prone to triplet‐triplet annihilation due to its spatial confinement. In the solid state, entropically driven triplet diffusion assists in the spatial separation of triplets, resulting in higher yields of free triplets. Control over electronic coupling in the solid state is, however, challenging given its sensitivity to molecular packing. We have thus developed a hexameric system (HexPnc) to enable solid‐state‐like triplet diffusion at the molecular scale. This system is realized by covalently tethering three pentacene dimers to a central subphthalocyanine scaffold. Transient absorption spectroscopy, complemented by theoretical structural optimizations and steady‐state spectroscopy, reveals that triplet diffusion is indeed facilitated due to intramolecular cluster formation. The yield of free triplets in HexPnc is increased by a factor of up to 14 compared to the corresponding dimeric reference (DiPnc). Thus, HexPnc establishes crucial design aspects for achieving efficient triplet dissociation in strongly coupled systems by providing avenues for diffusive separation of 1(T1T1), while, concomitantly, retaining strong interchromophore coupling which preserves rapid formation of 1(T1T1). [ABSTRACT FROM AUTHOR]

We investigate the introduction of bulky aryl substituents of the biphenyl, terphenyl, and quaterphenyl type at the 6,13 and 5,7,12,14 positions of the pentacene scaffold by reaction of the corresponding quinones with lithium organic reagents. The 1,1′‐biphenyl‐2‐yl substituent could be installed at the 5,7,12,14‐positions and regioselectively either at 6,13 or at the 5,13 positions. The unsymmetrical substitution motif results from concomitant 1,2 and 1,4‐addition to 6,13‐pentacenequinone. A one‐pot protocol leads to isomeric symmetric 6,13‐disubstituted pentacenes and allows installation of two 5′‐phenyl‐[1,1′:3′,1′′‐terphenyl]‐2‐yl substituents. The four new pentacenes differ in crystal packing and photochemical stability. [ABSTRACT FROM AUTHOR]

This work reports the fabrication and characterization of p-type organic metal–semiconductor–metal (MSM) Schottky barrier visible photodetector. The photodetector structure is interdigitated planar Al/pentacene/Al. Pentacene thin films were deposited by thermal vacuum deposition technique on an n-Si <111> substrate. The x-ray diffraction (XRD) measurement showed that the pentacene thin film exhibited a polycrystalline triclinic (anorthic) nature. The film's morphology was examined by scanning electron microscopy (SEM) which showed vertically aligned nanograins and distinct boundaries. Pentacene chemical analysis was performed using energy-dispersive x-rays (EDX). The optical properties of pentacene were studied by UV–visible (UV–VIS) absorbance spectra. The photodetector parameters were extracted from current–voltage (I–V) curves at room temperature under dark and illuminated conditions for applied voltages from − 4 V to 4 V and optical power ranging from 4 µw to 86.5 µw at 620 nm. The device's dark environment parameters have been analyzed by conventional thermionic theory and Cheung's functions. These parameters are compared with contrasts such as saturation current, barrier height, and ideality factor. The estimated photodetection parameters include responsivity (3.37 A/W), detectivity (5.59 × 108 mHz½W−1), and sensitivity (4.65), and the device exhibited an external quantum efficiency of more than 1 (675%). The capacitance–voltage (C–V) characteristics at different frequencies were also examined. The doping concentration, space charge width, the built-in voltage, barrier height, and maximum electric field were extracted from the C–V measurements. The results of the study reveal that the Al/pentacene/Al organic MSM contact fabricated by a simple vacuum thermal deposition technique can be used as a substitute for inorganic visible photodiode applications. [ABSTRACT FROM AUTHOR]

Dimerization of polycyclic aromatic hydrocarbons (PAHs) is an important, yet poorly understood, step in the on-surface synthesis of graphene (nanoribbon), soot formation, and growth of carbonaceous dust grains in the interstellar medium (ISM). The on-surface synthesis of graphene and the growth of carbonaceous dust grains in the ISM require the chemical dimerization in which chemical bonds are formed between PAH monomers. An accurate and cheap method of exploring structure rearrangements is needed to reveal the mechanism of chemical dimerization on surfaces. This work has investigated the chemical dimerization of two dehydrogenated PAHs (coronene and pentacene) on graphene via an evolutionary algorithm augmented by machine learning surrogate potentials and a set of customized structure operators. Different dimer structures on surfaces have been successfully located by our structure search methods. Their binding energies are within the experimental errors of temperature programmed desorption measurements. The mechanism of coronene dimer formation on graphene is further studied and discussed. [ABSTRACT FROM AUTHOR]

In this work, we present a novel force-based scheme to perform hybrid quantum mechanics/molecular mechanics (QM/MM) computations. The proposed scheme becomes especially relevant for the simulation of host–guest molecular systems, where the description of the explicit electronic interactions between a guest molecule and a classically described host is of key importance. To illustrate its advantages, we utilize the presented scheme in the geometry optimization of a technologically important host–guest molecular system: a pentacene-doped p-terphenyl crystal, a core component of a room-temperature MASER device. We show that, as opposed to the simpler and widely used hybrid scheme ONIOM, our Quantum-Coupling QM/MM scheme was able to reproduce explicit interactions in the minimum energy configuration for the host–guest complex. We also show that, as a result of these explicit interactions, the host–guest complex exhibits an oriented net electric dipole moment that is responsible for red-shifting the energy of the first singlet–singlet electronic excitation of pentacene. [ABSTRACT FROM AUTHOR]

This paper presents a performance analysis of indium-gallium-zinc-oxide (IGZO)- and pentacene-based top-gate-top-contact (TGTC) and bottom-gate-top-contact (BGTC) thin film transistors (TFTs). Extensive simulation has been performed to assess the performances in terms of threshold voltage, subthreshold slope, on-off current ratio, mobility, and figure of merit (FoM). Results indicate a trade-off between mobility and current ratio with respect to the permittivity of the dielectric layer, where tantalum oxide (Ta2O 5) provides the optimum result in terms of FoM. The mobility of IGZO is significantly higher for both structures, whereas the current ratio for IGZO is higher than pentacene in the BGTC configuration. Comparing the structural configurations, Ta2O5-IGZO-based BGTC achieves 5. 9 2 × and 4 1. 8 × better mobility and current ratio, respectively, over TGTC structures. The threshold voltage of IGZO-based TFT is observed to increase with the permittivity of the dielectric in TGTC configuration but decrease in BGTC configuration. Meanwhile, the increase in oxide and active layer thicknesses causes a decrease in the threshold voltage. Moreover, both mobility and current ratio improve with a decrease in oxide or active layer thickness. Maximum mobility of 32.30 cm2/Vs and a maximum current ratio of 7.54E+08 are achieved for Ta2O5-IGZO-based BGTC TFT with 10 μ m channel thickness and 5 μ m oxide thickness. [ABSTRACT FROM AUTHOR]

Nanoscale-thick organic/inorganic hybrid heterojunction functioning as the core optical active layer of a photodetector has many significant advantages due to its enhanced light absorption, excellent interface quality, higher mechanical stability, and intralayer excitonic dynamics. However, via controlled growth of high-quality 2D pentacene/Bi2Se3 heterojunction to further improve the performance metrics of photodetectors has rarely been investigated. Therefore, to further explore its utilization potentiality in optoelectronics, the newly conceived organic/inorganic heterojunctions with sharp interface were controllably grown based on small-molecule pentacene and topological insulator Bi2Se3 nanometer films. Then, a self-driven and blue-sensitive heterojunction photodetector was fabricated. Note that the photodetector with nanoscale thickness exhibits a reversible photocurrent switching performance with higher photoresponsivity of 4.834 A/W and detectivity of 1.62 × 1010 Jones under 405 nm blue-light irradiation. Through integrating several surface-sensitive characterization techniques, the robust interface Schottky potential was experimentally revealed, which was derived from the metallic and few nanometers thick Dirac surface state of the Bi2Se3 crystal. This contact behavior is beneficial to improve the separation capability of electron–hole pairs and promotes the photoelectric conversion efficiency of the heterojunction. This study provides an in-depth understanding of the basic photophysics of pentacene/Bi2Se3 heterojunctions, and the newly designed photodetector has broad application prospects in low-power and flexible optoelectronics. [ABSTRACT FROM AUTHOR]

Singlet exciton fission (SF), the formation of two triplet excitons from one singlet exciton, involves electronic, nuclear, and spin degrees of freedom as well as their couplings. Despite almost 60 years of research on this process, a complete microscopic understanding is still missing. One important open question concerns the role of nuclear motion in SF. In this perspective, recent results on the exciton dynamics are related to the structural dynamics of single‐crystal pentacene and how they provide insights into that open question is shown. To probe the electronic dynamics, orbital‐resolved measurements of the electronic structure are carried out using time‐ and angle‐resolved photoemission spectroscopy. With femtosecond electron diffraction and with ab initio computations, the complementary nuclear dynamics is tracked. The results from both techniques are summarized, and how they relate to each other is discussed. Then, remaining open questions are outlined and potential routes are identified to tackle them, hopefully guiding future studies. [ABSTRACT FROM AUTHOR]

Mobility is an important parameter to estimate the performance of organic thin‐film transistors, one of the key factors affecting the mobility is the first several semiconductors molecular layers near the insulator surface. A strategy is proposed to introduce aromatic‐rings in the gate insulating layer to modulate the growth of pentacene, thus a series of aryl group containing polymers by reversible‐addition‐fragmentation chain‐transfer polymerization is synthesized for the preparation of organic thin‐film transistor insulators. The semiconductor layer is evaporated on the polymer insulators at room temperature. As the inducing function of the aromatic ring, greater weak interactions between dielectric materials and semiconductors by simulation, which makes the initial pentacene layer weak epitaxial growth, therefore pentacene could form better morphology, especially larger crystal domains and uniform thin‐film continuity. The results show that precision design and synthesis of polymer insulator layers provide new methods to achieve high performance of organic thin‐film transistors with easier fabricating process. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) light has many applications in agriculture, transportation, medicine, the military, and other fields. Lead phthalocyanine (PbPc) exhibits excellent near-infrared (NIR) light absorption characteristics and is widely used in NIR-sensitive organic photodetectors. In this work, PbPc-based NIR organic phototransistors (OPTs) with different active layer structures were designed and fabricated. The photo-absorption characteristics of organic films, photosensitive properties, and air stability of the devices were investigated. The results suggested that (i) the bilayer planar heterojunction (PHJ) devices exhibit far better photosensitive performance than the single layer ones due to higher mobility of the formers than the latters; (ii) the bilayer PHJ ones with p-type channel have equivalent photosensitive performance to those with n-type channel owing to equivalent mobility, higher NIR absorption and lower exciton dissociation efficiency of the formers than the latters; (iii) the bilayer PHJ ones with p-type channel possess superior air stability to those with n-type channel thanks to better air stability of pentacene channel layer than C60 channel layer; (iv) the tri-layer PHJ ones perform better than the bilayer PHJ ones with p-type channel and exhibit a high photoresponsivity of 1415 mA/W and a maximum photo-to-dark current ratio of 1.2 × 104, and such an outstanding performance benefits from the virtues of tri-layer PHJ structure including high light absorption, carrier mobility and exciton dissociation efficiency; and (v) the air stability of the tri-layer PHJ ones is better than that of the bilayer PHJ ones with p-type channel, which can be attributed to the passivation of the top-level C60 layer. [ABSTRACT FROM AUTHOR]

In this work, we have done the comparative analysis of Single Gate and Dual Gate pentacene-based organic phototransistors (OPT). The opto-electrical simulations were done using 2-D Silvaco TCAD ATLAS device simulator. The SG-OPT and DG-OPT were simulated to provide deeper insight into behaviour of the two from both device physics perspective and quantitative standpoints. We have conducted an evaluation of both OPTs on account of the various important performance parameters at different electrical and optical bias over a wide spectral range. Our results shows how these different configurational OPT designs can influence the essential performance parameters while observing the variations in drain current, Current density, Energy band Diagrams and the various essential performance parameters such as Responsivity, photosensitivity, spectral response, quantum efficiency etc. [ABSTRACT FROM AUTHOR]

The vacuum process using small molecule-based organic materials to make organic photodiodes (OPDIs) will provide many promising features, such as well-defined molecular structure, large scalability, process repeatability, and good compatibility for CMOS integration, compared to the widely used Solution process. We present the performance of planar heterojunction OPDIs based on pentacene as the electron donor and C60 as the electron acceptor. In these devices, MoO3 and BCP interfacial layers were interlaced between the electrodes and the active layer as the electron- and hole-blocking layer, respectively. Typically, BCP played a good role in suppressing the dark current by two orders higher than that without that layer. These devices showed a significant dependence of the performance on the thickness of the pentacene. In particular, with the pentacene thickness of 25 nm, an external quantum efficiency at the 360 nm wavelength according to the peak absorption of C60 was enhanced by 1.5 times due to a cavity effect, compared to that of the non-cavity device. This work shows the importance of a vacuum processing approach based on small molecules for OPDIs, and the possibility of improving the performance via the optimization of the device architecture. [ABSTRACT FROM AUTHOR]

Few‐layer black phosphorus (FL‐BP) shows great potential in infrared polarization‐sensitive photodetection due to its narrow bandgap and strong in‐plane anisotropy. However, FL‐BP is easy to be oxidized and degraded, which severely restricts its applications. Herein, a simple and scalable in situ interfacial passivation method based on pentacene film is reported to enhance the ambient stability of FL‐BP as well as achieve n‐type doping for improved polarization‐sensitive photoimaging. High crystal quality FL‐BP flakes with intrinsic anisotropy are prepared by electrochemical exfoliation. The morphology and Raman spectra of FL‐BP/pentacene exhibit excellent stability 28 days after passivation. In addition, the hole mobility is significantly enhanced and dark current is substantially suppressed due to the interfacial passivation and n‐type doping effect. The FL‐BP/Pentacene based photodetector shows a broadband response from visible to near‐infrared with good stability. The photoresponsivity under 915 nm illumination is calculated as 2.2 mA W−1 with an anisotropy ratio of 1.29. Furthermore, the polarization imaging under the irradiation at zigzag and armchair directions directly reveals the strong infrared polarization‐sensitive imaging capability of FL‐BP/pentacene. This work also opens up new avenues to enhance the photoresponse and stability of various optoelectronics based on similarly unstable 2D materials. [ABSTRACT FROM AUTHOR]

Here, we present a concise model that can predict the photoluminescent properties of a given compound from first principles, both within and beyond the Franck–Condon approximation. The formalism required to compute fluorescence, Internal Conversion (IC), and Inter-System Crossing (ISC) is discussed. The IC mechanism, in particular, is a difficult pathway to compute due to difficulties associated with the computation of required bosonic configurations and non-adiabatic coupling elements. Here, we offer a discussion and breakdown on how to model these pathways at the Density Functional Theory (DFT) level with respect to its computational implementation, strengths, and current limitations. The model is then used to compute the photoluminescent quantum yield (PLQY) of a number of small but important compounds: anthracene, tetracene, pentacene, diketo-pyrrolo-pyrrole (DPP), and Perylene Diimide (PDI) within a polarizable continuum model. Rate constants for fluorescence, IC, and ISC compare well for the most part with respect to experiment, despite triplet energies being overestimated to a degree. The resulting PLQYs are promising with respect to the level of theory being DFT. While we obtained a positive result for PDI within the Franck–Condon limit, the other systems require a second order correction. Recomputing quantum yields with Herzberg–Teller terms yields PLQYs of 0.19, 0.08, 0.04, 0.70, and 0.99 for anthracene, tetracene, pentacene, DPP, and PDI, respectively. Based on these results, we are confident that the presented methodology is sound with respect to the level of quantum chemistry and presents an important stepping stone in the search for a tool to predict the properties of larger coupled systems. [ABSTRACT FROM AUTHOR]

Triplet dynamic nuclear polarization (triplet-DNP) is a technique that can obtain high nuclear polarization under moderate conditions. However, in order to obtain practically useful polarization, large single crystals doped with a polarizing agent must be strictly oriented with respect to the magnetic field to sharpen the electron spin resonance (ESR) spectra, which is a fatal problem that prevents its application to truly useful biomolecular targets. Instead of this conventional physical approach of controlling crystal orientation, here, we propose a chemical approach, i.e., molecular design of polarizing agents; pentacene molecules, the most typical triplet-DNP polarizing agent, are modified so as to make the triplet electron distribution wider and more isotropic without loss of the triplet polarization. The thiophene-modified pentacene exhibits a sharper and stronger ESR spectrum than the parent pentacene, and state-of-the-art quantum chemical calculations revealed that the direction of the spin polarization is altered by the modification with thiophene moieties and the size of D and E parameters are reduced from parent pentacene due to the partial delocalization of spin densities on the thiophene moieties. The triplet-DNP with the new polarizing agent successfully exceeds the previous highest ¹H polarization of glassy materials by a factor of 5. This demonstrates the feasibility of a polarizing agent that can surpass pentacene, the best polarizing agent for more than 30 y since triplet-DNP was first reported, in the unoriented state. This work provides a pathway toward practically useful high nuclear polarization of various biomolecules by triplet-DNP. [ABSTRACT FROM AUTHOR]

In this work, a facile and versatile strategy for the synthesis of contorted polycyclic aromatic hydrocarbons (PAHs) starting from the functionalized pentacene was established. A series of novel PAHs 1–4 and their derivatives were synthesized through a simple two‐step synthesis procedure involving an intramolecular reductive Friedel–Crafts cyclization of four newly synthesized pentacene aldehydes 5–8 as a key step. All the molecules were confirmed by single‐crystal X‐ray diffraction and their photophysical and electrochemical properties were studied in detail. Interestingly, the most striking feature of 1–4 is their highly contorted carbon structures and the accompanying helical chirality. In particular, the optical resolution of 2 was successfully achieved by chiral‐phase HPLC, and the enantiomers were characterized by circular dichroism and circularly polarized luminescence spectroscopy. Despite the highly nonplanar conformations, these contorted PAHs exhibited emissive properties with moderate‐to‐good fluorescence quantum yields, implying the potential utility of this series PAHs as high‐quality organic laser dyes. By using a self‐assembly method with the help of epoxy resin, a bottle microlaser based on 3 a was successfully illustrated with a lasing wavelength of 567.8 nm at a threshold of 0.3 mJ/cm2. We believe that this work will shed light on the chemical versatility of pentacene and its derivatives in the construction of novel functionalized PAHs. [ABSTRACT FROM AUTHOR]

We present the spectral properties of a selection of comets from both the Jupiter family and Oort cloud in the ultraviolet (UV) and mid-infrared (IR) wavelength regions. Spectroscopic measurements are retrieved from public archival data of the International Ultraviolet Explorer (IUE) and Hubble Space Observatory (HST) in the near-UV (NUV) and far-UV (FUV) wavelengths and reveal emissions from Polycyclic Aromatic Hydrocarbon (PAH) molecules, such as pentacene (C 22 H 14 ) at 1902, 2795 Å and toluene (C 7 H 8 ) at 2681 Å. UV spectra of the comets also show emissions due to CS, Fe II, CO Cameron bands, C I, S I and O I. Mid-IR spectroscopic observations made using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope for a few comets reveal the presence of PAH bands at 6.2, 7.7, 8.6, 11.2 μ m. Mid-IR spectra of the comets also reveal the presence of silicate at 9.7 μ m. The similarity of PAH signatures observed in the proto-planetary disks of young stellar objects, meteorites, interplanetary dust particles and comets with those observed in the interstellar medium (ISM) suggests a possible scenario for the incorporation of PAH from ISM into the primordial solar nebula. [ABSTRACT FROM AUTHOR]

In the present work, the energy donor 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) is used for the first time in combination with a pentacene dimer (Pnc2) to provide the conjugate BODIPYPnc2 that features absorption throughout a large part of the solar spectrum. Upon photoexcitation, the singlet excited state energy of BODIPY is transferred to the pentacene dimer via intramolecular Förster resonance energy transfer (FRET). Subsequently, the pentacene dimer undergoes intramolecular singlet fission. In this process, a singlet correlated triplet pair is generated from the first singlet excited state via coupling to an intermediate state. The results show that solvent polarity has an influence on the system, with the largest FRET rate (i.e., 7.46 × 1011 s−1) being obtained in the most polar solvent (namely, benzonitrile) along with the largest triplet quantum yield (i.e., 207 ± 20%). [ABSTRACT FROM AUTHOR]

NdON, HfON, and their mixtures (NdxHf(1−x)ON) with different Hf contents are adopted as the gate dielectrics of pentacene organic thin‐film transistors (OTFTs). Their capacitance–voltage characteristics reveal that the Hf incorporation generates negative fixed charges in the dielectric for assisting the applied gate voltage, thus achieving a low threshold voltage for the OTFT. X‐ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) results indicate that Hf can suppress the hygroscopicity of Nd oxide while Nd can passivate the carrier traps (e.g., oxygen vacancies) of Hf oxide, both of which can contribute to a smoother dielectric surface for the growth of larger pentacene grains on the dielectric surface. As a result, among the samples with different Hf contents, the OTFT with Nd0.85Hf0.15ON can achieve the highest carrier mobility of 1.95 cm2 V−1 s−1 due to least Coulomb scattering (associated with lowest interface‐trap density of 5.9 × 1012 cm−2 eV−1 and smallest hysteresis of 0.26 V) and least grain‐boundary scattering (associated with largest pentacene grains). [ABSTRACT FROM AUTHOR]

Density functional approximations (DFAs) are known to significantly overestimate the polarizabilities of long chain-like molecules. We study the static electric dipole polarizabilities and the vertical ionization potentials of polyacenes from benzene to pentacene using the Fermi–Löwdin orbital-based self-interaction corrected (FLOSIC) density functional method. The orbital by orbital self-interaction correction corrects for the overestimation tendency of DFAs. The polarizabilities calculated with FLOSIC-DFA are, however, overly corrected. We also tested the recently developed locally scaled self-interaction correction (LSIC) method on polyacenes. The local-scaling method applies full SIC in the one-electron regions and restores the proper behavior of the SIC exchange–correlation functionals in the uniform density limit. The results show that LSIC removes the overcorrection tendency of the FLOSIC-DFA and produces results that are in excellent agreement with reference coupled-cluster single and double values. The vertical ionization potentials with LSIC also show good agreement with available experimental values. [ABSTRACT FROM AUTHOR]

Transistor-based artificial synapses are expected to tackle the inherent limitations of traditional von Neumann architecture for neuromorphic computing paradigm. Organic electronic materials are promising components of future neuromorphic systems, but mimicking the functions of biological synapses for symmetric weight update and desired variation margin still remains challenging. Here, we propose a synaptic transistor based on pentacene/poly(α-methylstyrene) (PαMS) architecture capable of exhibiting the main behavior of a biological spiking synapse. The ambipolar charge trapping of the transistor enables symmetric variation of the channel conductivity with desirable margin. Comprehensive synaptic functions, including the postsynaptic current with different pulse amplitudes, short-term to long-term plasticity transition, reversible channel conductance potentiation and depression, and repetitive and symmetrical learning processes, are emulated. The realization of essential synaptic functions based on the cumulative charge trapping of pentacene/PαMS structure provides a feasible device structure toward the future demand of neuromorphic computing. [ABSTRACT FROM AUTHOR]

Atomistic modeling of energy and charge transfer at the heterojunction of organic solar cells is an active field with many remaining outstanding questions owing, in part, to the difficulties in performing reliable photodynamics calculations on very large systems. One approach to being able to overcome these difficulties is to design and apply an appropriate simplified method. Density-functional tight binding (DFTB) has become a popular form of approximate density-functional theory based on a minimal valence basis set and neglect of all but two center integrals. We report the results of our tests of a recent long-range correction (lc) [A. Humeniuk and R. Mitrić, J. Chem. Phys. 143, 134120 (2015)] for time-dependent (TD) lc-DFTB by carrying out TD-lc-DFTB fewest switches surface hopping calculations of energy and charge transfer times using the relatively new DFTBABY [A. Humeniuk and R. Mitrić, Comput. Phys. Commun. 221, 174 (2017)] program. An advantage of this method is the ability to run enough trajectories to get meaningful ensemble averages. Our interest in the present work is less in determining exact energy and charge transfer rates than in understanding how the results of these calculations vary with the value of the range-separation parameter (Rlc = 1/μ) for a model organic solar cell heterojunction consisting of a gas-phase van der Waals complex P/F made up of a single pentacene (P) molecule together with a single buckminsterfullerene (F) molecule. The default value of Rlc = 3.03 a0 is found to be much too small as neither energy nor charge transfer is observed until Rlc ≈ 10 a0. Tests at a single geometry show that the best agreement with high-quality ab initio spectra is obtained in the limit of no lc (i.e., very large Rlc). A plot of energy and charge transfer rates as a function of Rlc is provided, which suggests that a value of Rlc ≈ 15 a0 yields the typical literature (condensed-phase) charge transfer time of about 100 fs. However, energy and charge transfer times become as high as ∼300 fs for Rlc ≈ 25 a0. A closer examination of the charge transfer process P*/F → P+/F− shows that the initial electron transfer is accompanied by a partial delocalization of the P hole onto F, which then relocalizes back onto P, consistent with a polaron-like picture in which the nuclei relax to stabilize the resultant redistribution of charges. [ABSTRACT FROM AUTHOR]

We investigate the ability of dynamic fluorescence probes to accurately track populations of multi-excitonic states in molecular dyads based on conjugated acenes capable of intramolecular singlet fission (iSF). Stochastic simulations of reported photophysical models from time-resolved spectroscopic studies of iSF dyads based on large acenes (e.g., tetracene and pentacene) are used to extrapolate population and fluorescence yield dynamics. The approach entails the use of repetitive rectangular-shaped excitation waveforms as a stimulus, with durations comparable to triplet lifetimes. We observe unique dynamics signatures that can be directly related to relaxation of multi-exciton states involved over the entire effective time of singlet fission in the presence and absence of an excitation light stimulus. In particular, time-dependent fluorescence yields display an abrupt decay followed by slower rise dynamics appearing as a prominent "dip" feature in responses. The initial fast decrease in the fluorescence yield arises from the formation of triplet pairs and separated triplets that do not produce emission resembling a complete ground state bleach effect. However, relaxation of one separated triplet allows the system to absorb, and in some cases, this increases the fluorescence yield, causing rise dynamics in the emissive response. Our approach also permits extrapolation of all multi-exciton state population dynamics up to steady state conditions in addition to the ability to explore consequences of alternative relaxation channels. The results demonstrate that it is possible to resolve unique signatures of singlet fission events from dynamic fluorescence studies, which can augment detection capabilities and extend sensitivity limits and accessible time scales. [ABSTRACT FROM AUTHOR]

Electron–phonon coupling plays a central role in the transport properties and photophysics of organic crystals. Successful models describing charge- and energy-transport in these systems routinely include these effects. Most models for describing photophysics, on the other hand, only incorporate local electron–phonon coupling to intramolecular vibrational modes, while nonlocal electron–phonon coupling is neglected. One might expect nonlocal coupling to have an important effect on the photophysics of organic crystals because it gives rise to large fluctuation in the charge-transfer couplings, and charge-transfer couplings play an important role in the spectroscopy of many organic crystals. Here, we study the effects of nonlocal coupling on the absorption spectrum of crystalline pentacene and 7,8,15,16-tetraazaterrylene. To this end, we develop a new mixed quantum–classical approach for including nonlocal coupling into spectroscopic and transport models for organic crystals. Importantly, our approach does not assume that the nonlocal coupling is linear, in contrast to most modern charge-transport models. We find that the nonlocal coupling broadens the absorption spectrum non-uniformly across the absorption line shape. In pentacene, for example, our model predicts that the lower Davydov component broadens considerably more than the upper Davydov component, explaining the origin of this experimental observation for the first time. By studying a simple dimer model, we are able to attribute this selective broadening to correlations between the fluctuations of the charge-transfer couplings. Overall, our method incorporates nonlocal electron–phonon coupling into spectroscopic and transport models with computational efficiency, generalizability to a wide range of organic crystals, and without any assumption of linearity. [ABSTRACT FROM AUTHOR]

Theoretical molecular design of efficient nonlinear optical (NLO) systems using singlet fission (SF) is performed for butterfly-shaped acenes with/without nitrogen and sulfur substitutions using quantum chemical calculations, exciton dynamics simulations, and Marcus theory. It is found that these large systems meet the energy level matching conditions of efficient SF and exhibit superior third-order NLO properties (second hyperpolarizability γ at the molecular scale) to a typical SF molecule, pentacene. In addition, we investigate SF rates and γ in the correlated triplet pair [1(TT)] state generated by SF for various slip-stacked dimer models of these systems. For molecular packing with relatively large 1(TT) yields, a significant increase in γ/monomer in the 1(TT) state is observed, which is in good agreement with the electronic-coupling-based design guidelines obtained from our previous study. In particular, the butterfly-shaped acenes involving heteroatoms are found to exhibit a significant increase in γ/monomer as compared to the other systems. By analyzing the excitation properties in the 1(TT) state and intermolecular orbital interactions, we clarify the origin of such γ enhancement. The obtained results contribute to the construction of design guidelines for efficient SF-induced-NLO materials and demonstrate that butterfly-shaped acenes have the potential to surpass conventional NLO systems. [ABSTRACT FROM AUTHOR]

Polysilsesquioxane (PSQ) is used to make gate dielectric layers with pentacene to create thin‐film transistors (TFTs) by incorporating 3‐mercaptopropyl functional groups for UV light‐initiated thiol–ene polymerization with vinyl‐containing cross‐linkers. The dielectric constant (ε) of the polymerized PSQ films is controlled by the ratio of 3‐mercaptopropyl groups. When the 3‐mercaptopropyl group comprises 20%, it yields a polymerized film with a ε of 4.2 ± 0.2; upon decreasing this proportion to 10%, the ε for the subsequent film became 3.5 ± 0.2. The hole mobility of the fabricated pentacene TFTs is observed to increase as ε decreases, reaching a maximum of 0.96 cm2 V−1 s−1. [ABSTRACT FROM AUTHOR]

The understanding of crystal formation in thin films and the precise knowledge of the relation between structure and surface diffusion are two important requirements for the efficient (nano)fabrication of organic electronic devices. Here a computational approach for simulating vapor‐phase deposition is employed to obtain and investigate three types of crystalline thin films on graphite. All systems, namely pentacene, perfluoropentacene, and their 1:1 blend, which forms an alternate cocrystal, are constituted by recumbent molecules in accordance with experimental findings. The contributions of intermolecular interactions and of molecular rearrangements occurring during the deposition are analyzed to rationalize the final morphologies. Then, the generated structures are employed to evaluate the energy barriers that prevent molecular diffusion at terraces and step‐edges, and to study the reorganization of the films upon high‐temperature annealing. The broad agreement with experimental observations and the possibility of evaluating the potential energy surface at the molecular detail render the proposed approach a promising tool to make predictions for other systems. [ABSTRACT FROM AUTHOR]