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The second-order nonlinear optical properties of four series of amphiphilic cationic chromophores have been investigated by means of electric field induced second harmonic generation and by combining molecular dynamics and quantum chemical calculations.

ConspectusThe last 30 years have witnessed an ever-growing application of computational chemistry for rationalizing the nonlinear optical (NLO) responses of organic chromophores. More specifically, quantum chemical calculations proved highly helpful in gaining fundamental insights into the factors governing the magnitude and character of molecular first hyperpolarizabilities (β), be they either intrinsic to the chromophore molecular structure and arising from symmetry, chemical substitution, or π-electron delocalization, or induced by external contributions such as the laser probe or solvation and polarization effects. Most theoretical reports assumed a rigid picture of the investigated systems, the NLO responses being computed solely at the most stable geometry of the chromophores. Yet, recent developments combining classical molecular dynamics (MD) simulations and DFT calculations have evidenced the significant role of structural fluctuations, which may induce broad distributions of NLO responses, and even generate them in some instances.This Account presents recent case studies in which theoretical simulations have highlighted these effects. The discussion specifically focuses on the simulation of the second-order NLO properties that can be measured experimentally either from Hyper-Rayleigh Scattering (HRS) or Electric-Field Induced Second Harmonic Generation (EFISHG). More general but technical topics concerning several aspects of the calculations of hyperpolarizabilities are instead discussed in the Supporting Information.Selected examples include organic chromophores, photochromic systems, and ionic complexes in the liquid phase, for which the effects of explicit solvation, concentration, and chromophore aggregation are emphasized, as well as large flexible systems such as peptide chains and pyrimidine-based helical polymers, in which the relative variations of the responses were shown to be several times larger than their average values. The impact of geometrical fluctuations is also illustrated for supramolecular architectures with the examples of nanoparticles formed by organic dipolar dyes in water solution, whose soft nature allows for large shape variations translating into huge fluctuations in time of their NLO response, and of self-assembled monolayers (SAMs) based on indolino-oxazolidine or azobenzene switches, in which the geometrical distortions of the photochromic molecules, as well as their orientational and positional disorder within the SAMs, highly impact their NLO response and contrast upon switching. Finally, the effects of the rigidity and fluidity of the surrounding are evidenced for NLO dyes inserted in phospholipid bilayers.

International audience; Graphene quantum dots, atomically precise nanopieces of graphene, are promising nanoobjects with potential applications in various domains such as photovoltaics, quantum light emitters or bio-imaging. Despite their interesting prospects, precise reports on their photophysical properties remain scarce. Here, we report on a study of the photophysics of C$_{96}$H$_{24}$(C$_{12}$H$_{25}$) graphene quantum dots. A combination of optical studies down to the single molecule level with advanced molecular modeling demonstrates the importance of the coupling to vibrations in the emission process. Optical fingerprints for H-like aggregates are identified. Our combined experimental-theoretical investigations provide a comprehensive description of the light absorption and emission properties of nanographenes, which not only represents an essentiel step towards precise control of sample production, but also paves the way for new exciting physics focused on twisted graphenoid.

Recent years have shown an increasing number of studies dedicated to new light emitters for diverse applications such as optoelectronics, bio-imaging, and quantum technologies. In this context, graphene quantum dots (GQD) have important assets since bottom-up chemistry allows complete control of the structure, opening the way to wide customization of their electronic, optical, and spin properties [1-3]. The full benefit from these opportunities requires addressing GQD’s intrinsic photophysical properties.To do so, single molecule photoluminescence experiment is a powerfull tool [4]. Here, we highlight the influence of vibrations on GQDs’ optical properties, by comparing optical studies to extensive DFT/TDDFT calculations combined with molecular dynamics simulations. Specifically, we discussed their role in the transitions' oscillator strengths [5]. In order to get deeper in the photophysics of GQD, we investigate the spectroscopy of single GQDs at cryogenic temperatures. In particular, we show a narrowing of the emission lines at low temperature, that allows us to characterize and identify vibrational replicas that are characteristic to GQDs [6]. [1] M. G. Debije, J. Am. Chem. Soc. 2004, 126, 4641 [2] X. Yan, X. Cui, and L.-s. Li, J. Am. Chem. Soc. 2010 132, 5944 [3] A. Konishi et al, J. Am. Chem. Soc. 2010, 132, 11021 [4] S. Zhao et al, Nature Communications, 2018, 9, 3470 [5] T. Liu et al, under review [6] T. Liu et al, in preparation

Tin(IV) phthalocyanines (SnPcs) are promising candidates for low-cost organic electronic devices, and have been employed in organic photovoltaics (OPVs) and organic thin-film transistors (OTFTs). However, they remain relatively understudied compared to their silicon phthalocyanine (SiPc) analogues. Previously, we reported the first solution-processed SnPc semiconductors for OTFTs and OPVs; however, the performances of these derivatives were unexpected. Herein to further study the behavior of these derivatives in OPVs and OTFTs, we report the synthesis along with optical and thermal characterization of seven axially substituted (OR)2-SnPcs, five of which were synthesized for the first time. Density functional theory (DFT) was used to predict charge-carrier mobilities for our materials in their crystal state. The application of these SnPcs as ternary additives in poly(3-hexylthiophene) (P3HT)/phenyl-C61-butyric acid methyl ester (PC61BM) OPVs and as semiconductors in solution-processed n-type OTFTs was also investigated. When employed as ternary additives in OPVs, all (OR)2-SnPcs decreased the power conversion efficiency, open-circuit voltage, short-circuit current, and fill factor. However, in OTFTs, four of the seven materials exhibited greater electron field-effect mobility with similar threshold voltages compared to their previously studied SiPc analogues. Among these SnPcs, bis(triisobutylsilyl oxide) SnPc displayed the greatest electron field-effect mobility of 0.014 cm2 V-1 s-1, with a threshold voltage of 31.4 V when incorporated into OTFTs. This difference in electrical performance between OTFT and OPV devices was attributed to the low photostability of SnPcs.

Observation of the neutrinoless double β decay is the only practical way to establish that neutrinos are their own antiparticles. Because of the small masses of neutrinos, the lifetime of neutrinoless double β decay is expected to be at least ten orders of magnitude greater than the typical lifetimes of natural radioactive chains, which can mimic the experimental signature of neutrinoless double β decay. The most robust identification of neutrinoless double β decay requires the definition of a signature signal—such as the observation of the daughter atom in the decay—that cannot be generated by radioactive backgrounds, as well as excellent energy resolution. In particular, the neutrinoless double β decay of Xe could be established by detecting the daughter atom, Ba, in its doubly ionized state. Here we demonstrate an important step towards a ‘barium-tagging’ experiment, which identifies double β decay through the detection of a single Ba ion. We propose a fluorescent bicolour indicator as the core of a sensor that can detect single Ba ions in a high-pressure xenon gas detector. In a sensor made of a monolayer of such indicators, the Ba dication would be captured by one of the molecules and generate a Ba-coordinated species with distinct photophysical properties. The presence of such a single Ba-coordinated indicator would be revealed by its response to repeated interrogation with a laser system, enabling the development of a sensor able to detect single Ba ions in high-pressure xenon gas detectors for barium-tagging experiments., We also acknowledge support from the following agencies and institutions: the European Research Council (ERC) under Advanced Grant 339787-NEXT; the Ministry of Science and Innovation of Spain and FEDER under grants FIS2014-53371-C04, FIS2016-76163-R, MAT2016-78293-C6-5-R, MINECO/FEDER CT2016-80955-P, CTQ2016-80375-P and CTQ2014-51912-REDC; Interred PCTEFA V-A Spain/France/Andorra Program (EFA 194/16/TNSI); the Basque Government (GV/EJ) under grants IT-1346-19 and IT-1180-19; andAgencia de Ciencia y Tecnología de la Región de Murcia (19897/GERM/15). The authors also thank the SGI/IZO-SGIker UPV/EHU, Fundación Séneca and DIPC for computational and analytical resources.

Silicon phthalocyanine (SiPc) derivatives have recently emerged as promising materials for n-type organic thin-film transistors (OTFTs) with the ability to be fabricated either by solid state or solution processes through axial functionalization. Among those, bis(tri-n-propylsilyl oxide) SiPc ((3PS)2-SiPc) is unique as it can be processed by sublimation, while being soluble enough for solution processing. In this work, the charge transport properties of (3PS)2-SiPc and its polymorphic forms were studied through Kinetic Monte Carlo (KMC) simulations and density functional theory (DFT) calculations along with the characterization of (3PS)2-SiPc in n-type OTFTs fabricated by physical vapour deposition (PVD) and spin coating. Post-deposition thin-film characterization by X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning transmission X-ray microscopy (STXM) was used to assess film morphology and microstructure in relation to the electrical performance of OTFTs. The differences in film formation by PVD and solution fabrication had little effect on OTFT performance with comparable field-effect mobility and threshold voltage ranging between 0.01–0.04 cm2 V−1 s−1 and 18–36 V respectively. Consistent charge transport properties of (3PS)2-SiPc OTFTs achieved at different fabrication conditions highlights the processing versatility of this material.

Engineering a low singlet-triplet energy gap (ΔEST) is necessary for efficient reverse intersystem crossing (rISC) in delayed fluorescence (DF) organic semiconductors but results in a small radiative rate that limits performance in LEDs. Here, we study a model DF material, BF2, that exhibits a strong optical absorption (absorption coefficient = 3.8 × 105 cm−1) and a relatively large ΔEST of 0.2 eV. In isolated BF2 molecules, intramolecular rISC is slow (delayed lifetime = 260 μs), but in aggregated films, BF2 generates intermolecular charge transfer (inter-CT) states on picosecond timescales. In contrast to the microsecond intramolecular rISC that is promoted by spin-orbit interactions in most isolated DF molecules, photoluminescence-detected magnetic resonance shows that these inter-CT states undergo rISC mediated by hyperfine interactions on a ~24 ns timescale and have an average electron-hole separation of ≥1.5 nm. Transfer back to the emissive singlet exciton then enables efficient DF and LED operation. Thus, access to these inter-CT states, which is possible even at low BF2 doping concentrations of 4 wt%, resolves the conflicting requirements of fast radiative emission and low ΔEST in organic DF emitters., A low singlet-triplet energy gap, necessary for delayed fluorescence organic semiconductors, results in a small radiative rate that limits performance in OLEDs. Here, the authors show that it is possible to reconcile these conflicting requirements in materials that can access both high oscillator strength intramolecular excitations and intermolecular charge transfer states.

Covalent assemblies of conjugated organic chromophores provide the opportunity to engineer new excited states with novel properties. In this work, a newly developed triple-stranded cage architecture, in which meta-substituted aromatic caps serve as covalent linking groups that attach to both top and bottom of the conjugated molecule walls, is used to tune the properties of thiophene oligomer assemblies. Benzene-capped and triazine-capped 5,5'-(2,2-bithiophene)-containing arylene cages are synthesized and characterized using steady-state and time-resolved spectroscopic methods. The conformational freedom and electronic states are analyzed using time-dependent density functional theory. The benzene cap acts as a passive spacer whose electronic states do not mix with those of the chromophore walls. The excited state properties are dominated by through-space interactions between the chromophore subunits, generating a neutral Frenkel H-type exciton state. This excitonic state undergoes intersystem crossing on a 200 ps time scale while the fluorescence output is suppressed by a factor of 2 due to a decreased radiative rate. Switching to a triazine cap enables electron transfer from the chromophore-linker after the initial excitation to the exciton state, leading to the formation of a charge-transfer state within 10 ps. This state can avoid intersystem crossing and exhibits red-shifted fluorescence with enhanced quantum yield. The ability to interchange structural modules with different electronic properties while retaining the overall cage morphology provides a new approach for tuning the properties of discrete chromophore assemblies.

Owing to their intense emission, low toxicity and solubility in aqueous medium, fluorescent organic nanoparticles (FONs) have emerged as promising alternatives to inorganic ones for the realization of exogenous probes for bioimaging applications. However, the intimate structure of FONs in solution, as well as the role played by intermolecular interactions on their optical properties, remains challenging to study. Following a recent Second-Harmonic Scattering (SHS) investigation led by two of us [Daniel et al., ACS Photonics, 2015, 2, 1209], we report herein a computational study of the structural organization and second-order nonlinear optical (NLO) properties of FONs based on dipolar chromophores incorporating a hydrophobic triphenylamine electron-donating unit and a slightly hydrophilic aldehyde electron-withdrawing unit at their extremities. Molecular dynamics simulations of the FON formation in water are associated with quantum chemical calculations, to provide insight into the molecular aggregation process, the molecular orientation of the dipolar dyes within the nanoparticles, and the dynamical behavior of their NLO properties. Moreover, the impact of intermolecular interactions on the NLO responses of the FONs is investigated by employing the tight-binding version of the recently developed simplified time-dependent density functional theory (sTD-DFT) approach, allowing the all-atom quantum mechanics treatment of nanoparticles. This journal is

International audience; We describe the synthesis and spectroscopic study of the bichromophoric molecule DA-meso consisting of two boron difluoride curcuminoid (BF 2-curcuminoid) units tethered by the rigid diacetylenic bridge. This structural feature imparts the quadrupolar-like DA-meso with a strong ability to self-assemble in solution, which induces a profound change in the optical properties. The UV-vis absorption spectrum of the aggregate is characterized by the appearance of a redshifted band at low energy and its fluorescence emission occurs in the near infrared ( max = 700 nm) with a low quantum yield (5 %). This is in contradiction with the strong emission expected for J-aggregates considering the Frenkel exciton model. From concentration-dependent UV-vis absorption spectroscopy we demonstrate the formation of a dimer composed of four BF 2-curcuminoid units. Single-crystal X-ray diffraction structure analysis and in-depth quantum chemical calculations based on density functional theory (DFT) and subsequent decomposition of the electronic excited states on a diabatic basis enable to discuss the geometry of the DA-meso dimer, and to establish the presence of excited states close in energy to that of the unperturbed monochromophore, which are not predicted by the classical Frenkel exciton model. Different dimer structures characterized by π-stacks of two and up to four chromophores are investigated, in which low-lying excited states with

The second-order nonlinear optical properties of 1,3-indandione-derived spirocyclohexadine compounds, a new class of photochromes showing sensitivity to both UV and visible lights, are investigated by means of density functional theory. The calculations predict that these compounds should display a large first hyperpolarizability variation upon commutation between their cyclic spiropyran and their merocyanine form. We also show that significant enhancement of the NLO response of the merocyanine form, as well as of the NLO contrast, can be achieved by means of appropriate chemical substitution, which makes these derivatives highly appealing for potential use in photo-responsive NLO devices.

Conjugated organic photochromes such as azobenzene derivatives can show remarkable nonlinear optical (NLO) properties and rapid responses, two essential requirements for the realization of optoelectronic switching devices. These applications also require the control of the molecular organization over the micrometric scale, which in principle can be achieved by arranging chromophore units in self-assembled monolayers (SAMs). To rationalize the interplay between the NLO responses of isolated molecules and those of photoresponsive materials, we implement here a computational approach combining molecular dynamics simulations and DFT calculations for predicting the contrast NLO responses of azobenzene-based SAMs with different surface densities. We show that collective switching of the chromophores is indeed possible, even though trans -> cis photoisomerization yields decrease when increasing the chromophore concentration. The magnitude of the second-order NLO response of trans SAMs is dominated by the component normal to the surface, which is considerably larger than the parallel one and significantly increases with the packing density. Photoswitching has the neat effect of halving the first hyperpolarizability, allowing for large NLO contrasts exploitable for storing and reading information in selected portions of the surface.

Pro-aromatic molecules have higher-energy diradicaloid states that are significantly influenced by resonance structures in which conjugated rings take on Hückel-aromatic character. Recently, it has been argued that there are also pro-aromatic molecules that adopt central units with 4npi-electron Baird-aromatic character in the T1 state, although detailed analysis suggests that these compounds are better labelled as T1 Hückel-Baird hybrid molecules where Hückel-aromaticity dominates. Herein, we consider a series of symmetrically substituted conjugated rings with potential Baird aromaticity in the lowest excited triplet and singlet states. Our computational results allow us to establish general guidelines for the rational design of molecules with excited state Hückel/Baird aromaticity in pro-aromatic quinoidal compounds. We found two main strategies to promote high Baird aromatic character: (i) anionic and small conjugated rings with electron donating groups as substituents and small exocyclic groups with electron withdrawing substituents, or (ii) electron deficient conjugated rings with exocyclic electron-donor substitution The authors thank the Ministerio de Economía y Competitividad of Spain (projects PGC2018-097722-B-I00, CTQ2017-85341-P, PGC2018-098212-B-C21, EUR2019-103825, and PID2019-109555GBI00), the Generalitat de Catalunya (project 2017SGR39 and the ICREA Academia prize 2019 awarded to A.P.), the Eusko Jaurlaritza (projects PIBA19-0004, IT1254-19, and 2019-CIEN-000092-01), and the Swedish Research Council (grant 2019-05618). S.E. thanks Universitat de Girona and DIPC for an IFUdG2019 PhD fellowship. A.P. is a Serra Húnter Fellow

Silicon phthalocyanines (SiPcs) have shown great potential as n-type or ambipolar organic semiconductors in organic thin-film transistors (OTFTs) and organic photovoltaics. Although properly designed SiPcs rival current state-of-the-art n-type organic semiconducting materials, relatively few structure−property relationships have been established to determine the impact of axial substituents on OTFT performance, hindering the intelligent design of the next generation of SiPcs. To address this omission, we have developed structure−property relationships for vapor-deposited SiPcs with phenoxy axial substituents. In addition to thorough electrical characterization of bottom-gate top-contact OTFTs, we extensively investigated SiPc thin films using X-ray diffraction, atomic force microscopy (AFM), grazing-incidence wide-angle X-ray scattering (GIWAXS), and density functional theory (DFT) modeling. OTFT performance, including relative electron mobility (μe) of materials, was in general agreement with values obtained through DFT modeling including reorganization energy. Another significant trend observed from device performance was that increasing the electron-withdrawing character of the axial pendant groups led to a reduction in threshold voltage (VT) from 47.9 to 21.1 V. This was corroborated by DFT modeling, which predicted that VT decreases with the square of the dipole induced at the interface between the SiPc pendant and substrate. Discrepancies between modeling predictions and experimental results can be explained through analysis of thin-film morphology and orientation by AFM and GIWAXS. Our results demonstrate that a combination of DFT modeling to select prospective candidate materials, combined with appropriate processing conditions to deposit molecules with a favorable thin-film morphology in an “edge-on” orientation relative to the substrate, yields high-performance n-type SiPc-based OTFTs.

The present study aims to provide a solid ground for the identification, characterization and controlled design of pro-aromatic quinoidal organic compounds holding conjugated rings with Hückel and/or Baird (singlet and triplet) excited state aromatic character, and expects to become a reference work for future studies on Baird-aromaticity. Concretely, we explore a wide range of compounds with a central conjugated ring of different sizes and symmetric exocyclic substitutions. We employ a combination of different computational tools and we also introduce a new energy-based approach for the quantification of the Baird-aromatic character. The key findings of this study indicate that Baird aromaticity is achieved in pro-aromatic quinoidal compounds having small anionic rings or in electron deficient rings with the proper exocyclic substitution. Low-lying states of these systems show very strong hole/electron overlaps, implying that their aromaticity cannot be related to intramolecular charge transfer.

Metal and metalloid phthalocyanines are an abundant and established class of materials widely used in the dye and pigment industry as well as in commercial photoreceptors. Silicon phthalocyanines (SiPcs) are among the highest-performing n-type semiconductor materials in this family when used in organic thin-film transistors (OTFTs) as their performance and solid-state arrangement are often increased through axial substitution. Herein, we study eight axially substituted SiPcs and their integration into solution-processed n-type OTFTs. Electrical characterization of the OTFTs, combined with atomic force microscopy (AFM), determined that the length of the alkyl chain affects device performance and thin-film morphology. The effects of high-temperature annealing and spin coating time on film formation, two key processing steps for fabrication of OTFTs, were investigated by grazing-incidence wide-angle X-ray scattering (GIWAXS) and X-ray diffraction (XRD) to elucidate the relationship between thin-film microstructure and device performance. Thermal annealing was shown to change both film crystallinity and SiPc molecular orientation relative to the substrate surface. Spin time affected film crystallinity, morphology, and interplanar d-spacing, thus ultimately modifying device performance. Of the eight materials studied, bis(tri-n-butylsilyl oxide) SiPc exhibited the greatest electron field-effect mobility (0.028 cm2 V-1 s-1, a threshold voltage of 17.6 V) of all reported solution-processed SiPc derivatives.

Atomically precise graphene quantum dots synthesized by bottom-up chemistry are promising versatile single emitters with potential applications for quantum photonic technologies. Toward a better understanding and control of graphene quantum dot (GQD) optical properties, we report on single-molecule spectroscopy at cryogenic temperature. We investigate the effect of temperature on the GQDs’ spectral linewidth and vibronic replica, which we interpret building on density functional theory calculations. Finally, we highlight that the vibronic signatures are specific to the GQD geometry and can be used as a fingerprint for identification purposes.

Photoswitchable self-assembled monolayers (SAMs) in contact with a conductive or semiconductive layer can be used to remotely trigger changes in electrical current using light. In this study, we apply full-atomistic simulations to assess the changes in electronic structure and charge-transport properties of a graphene sheet in contact with an amorphous silica dielectric decorated by an azobenzene SAM. The simulations explicitly account for the structural and electrostatic disorder sourced by the dielectric, which turns out to be weakly affected by photoisomerization and spatially correlated over a length scale of 4–5 nm. Most interestingly, by combining large-scale (tight binding) density functional theory with Kubo–Greenwood quantum transport calculations, we predict that the trans-cis isomerization should induce a shift in surface electrostatic potential by a few tenths of a volt, accompanied by a variation in conductivity by a factor of about 3.

International audience; The second harmonic signal of an amphiphilic dye embedded in a lipid bilayer has been calculated by combining molecular dynamics simulations and quantum chemistry calculations based on density functional theory. This computational approach provides insight into the morphology and dynamics of the fully hydrated biological system and the relationships linking the geometry and the environment of the dye to the amplitude of its second-order nonlinear optical response. The results point out a significant enhancement of the dynamic first hyperpolarizability of the dye induced by its interaction with the membrane and highlight the relative importance of dynamical, steric, and electrostatic effects. This computational scheme is thus particularly relevant for rationalizing the nonlinear optical contrasts revealed by second harmonic imaging microscopy of exogenous dyes embedded in biological media.

We report the first investigation of the second-order nonlinear optical (NLO) properties of donor-acceptor Stenhouse adducts (DASAs), an emerging class of colored photochromes that undergo photoswitching with visible light to a colorless form. By using time-dependent density functional theory, we provide insights into the relationships linking the nature of the chemical substituents to the amplitude and contrasts of the NLO response. Solvent and frequency dispersion effects are also analyzed. The calculations predict that DASAs behave as high contrast NLO switches, a finding that extends their potential applications to photo-responsive NLO materials and devices.

Photolabile protecting groups (PPGs) releasing bioactive compounds upon two-photon excitation have emerged as increasingly popular tools to control and study physiological processes. Yet the limited two-photon photosensitivity of many cages is still a critical issue for applications. We herein report the design, synthesis and photophysical study of polarized extended coumarinyl derivatives which show large two-photon sensitivity (up to 440 GM) at two complementary wavelengths in the NIR spectral range. DFT calculations demonstrate that subtle tuning of polarization in the ground-state and confinement of the photo-induced intramolecular charge transfer upon excitation is responsible for enhancing two-photon absorption while maintaining large uncaging efficiency. These findings open a new engineering route towards efficient coumarinyl PPGs.

The UV-vis electronic absorption and fluorescence emission properties of 8-halogenated (Cl, Br, I) difluoroboron dipyrrin (or 8-haloBODIPY) dyes and their 8-(C, N, O, S) substituted analogues are reported. The nature of the meso-substituent has a significant influence on the spectral band positions, the fluorescence quantum yields, and lifetimes. As a function of the solvent, the spectral maxima of all the investigated dyes are located within a limited wavelength range. The spectra of 8-haloBODIPYs display the narrow absorption and fluorescence emission bands and the generally quite small Stokes shifts characteristic of classic difluoroboron dipyrrins. Conversely, fluorophores with 8-phenylamino (7), 8-benzylamino (8), 8-methoxy (9), and 8-phenoxy (10) groups emit in the blue range of the visible spectrum and generally have larger Stokes shifts than common BODIPYs, whereas 8-(2-phenylethynyl)BODIPY (6) has red-shifted spectra compared to ordinary BODIPY dyes. Fluorescence lifetimes for 6, 8, and 10 have been measured for a large set of solvents and the solvent effect on their absorption and emission maxima has been analyzed using the generalized Catalán solvent scales. Restricted rotation about the C8-N bond in 7 and 8 has been observed via temperature dependent (1)H NMR spectroscopy, whereas for 10 the rotation about the C8-O bond is not hindered. The crystal structure of 8 demonstrates that the short C8-N bond has a significant double character and that this N atom exhibits a trigonal planar geometry. The crystal structure of 10 shows a short C8-O bond and an intramolecular C-H···π interaction. Quantum-chemical calculations have been performed to assess the effect of the meso-substituent on the spectroscopic properties.

We report on the synthesis of a novel perylene monoimide derivative that shows high response and selectivity for zinc ion detection. The complexation of Zn(2+) by the dye is followed by FD-MS, (1)H NMR, UV-vis spectroscopy, and isothermal titration calorimetry. Quantum chemical calculations are performed to gain further insight into the electronic processes responsible for the spectroscopic changes observed upon complexation. Finally, the perylene dye is incorporated in a sol-gel silica layer coated on optical fibers that are then used for Zn(2+) detection in aqueous solution.

The effect of varying the emitter concentration on the structural properties of an archetypal phosphorescent blend consisting of 4,4′-bis(N-carbazolyl)biphenyl and tris(2-phenylpyridyl)iridium(III) has been investigated using non-equilibrium molecular dynamics (MD) simulations that mimic the process of vacuum deposition. By comparison with reflectometry measurements, we show that the simulations provide an accurate model of the average density of such films. The emitter molecules were found not to be evenly distributed throughout film, but rather they can form networks that provide charge and/or energy migration pathways, even at emitter concentrations as low as ≈5 weight percent. At slightly higher concentrations, percolated networks form that span the entire system. While such networks would give improved charge transport, they could also lead to more non-radiative pathways for the emissive state and a resultant loss of efficiency.

Six conformationally restricted BODIPY dyes with fused carbocycles were synthesized to study the effect of conformational mobility on their visible electronic absorption and fluorescence properties. The symmetrically disubstituted compounds (2, 6) have bathochromically shifted absorption and fluorescence spectral maxima compared to those of the respective asymmetrically monosubstituted dyes (1, 5). Fusion of conjugation extending rings to the α,β-positions of the BODIPY core is an especially effective method for the construction of boron dipyrromethene dyes absorbing and emitting at longer wavelengths. The fluorescence quantum yields Φ of dyes 1-6 are high (0.7 ≤ Φ ≤ 1.0). The experimental results are backed up by quantum chemical calculations of the lowest electronic excitations in 1, 2, 5, 6, and corresponding dyes of related chemical structure but without conformational restriction. The effect of the molecular structure on the visible absorption and fluorescence emission properties of 1-6 has been examined as a function of solvent by means of the recent, generalized treatment of the solvent effect, proposed by Catalán (J. Phys. Chem. B 2009, 113, 5951-5960). Solvent polarizability is the primary factor responsible for the small solvent-dependent shifts of the visible absorption and fluorescence emission bands of these dyes.

Design of artificial systems, which can respond to fluctuations in concentration of adenosine phosphates (APs), can be useful in understanding various biological processes. Helical assemblies of chromophores, which dynamically respond to such changes, can provide real-time chiroptical readout of various chemical transformations. Towards this concept, here we present a supramolecular helix of achiral chromophores, which shows chiral APs responsive tunable handedness along with dynamically switchable helicity. This system, composing of naphthalenediimides with phosphate recognition unit, shows opposite handedness on binding with ATP compared with ADP or AMP, which is comprehensively analysed with molecular dynamic simulations. Such differential signalling along with stimuli-dependent fast stereomutations have been capitalized to probe the reaction kinetics of enzymatic ATP hydrolysis. Detailed chiroptical analyses provide mechanistic insights into the enzymatic hydrolysis and various intermediate steps. Thus, a unique dynamic helical assembly to monitor the real-time reaction processes via its stimuli-responsive chiroptical signalling is conceptualized.

The steady-state, UV-vis electronic absorption and fluorescence emission properties of a large set of 3-aryl and 3,5-diaryl substituted difluoroboron dipyrromethene dyes obtained via direct, palladium-catalyzed C-H (het)arylation of the BODIPY core are reported. The spectra display the narrow absorption and fluorescence emission bands and the generally quite small Stokes shifts characteristic of classic difluoroboron dipyrrins. As a function of the solvent, the spectral maxima are located within a very narrow wavelength range and are slightly red-shifted with increasing solvent polarizability, which is shown to be the crucial parameter influencing the wavelength position of the maxima. The extended π-conjugation in the 3,5-diaryl products always leads to bathochromically shifted absorption and emission spectra compared to those of the 3-aryl analogues. The derivative with a 3-mesityl substituent has blue-shifted spectra in comparison to its 3-phenyl substituted analogue, reflecting the diminished π-conjugation in the former due to steric strain. The nature of the meso-aryl has only a small effect on the spectral positions but affects the fluorescence quantum yield Φ. The majority of the dyes have high Φ (>0.85), except the compounds with meso-phenyl and meso-(p-nitrophenyl) substituents. Quantum-chemical calculations were performed to evaluate the differences in spectroscopic properties upon substitution of the BODIPY core and to compare them with the corresponding experimental results. ispartof: Photochemical & Photobiological Sciences vol:12 issue:5 pages:835-847 ispartof: location:England status: published

Starting from the conforma-tionally unconstrained compound 3, 5-di-(2-bromophenoxy)-4, 4-difluoro-8-(4-methylphenyl)-4-bora-3a, 4a-diaza-s-in-dacene (1), two BODIPY dyes (2 and 3) with increasingly rigid conformations were synthesized in outstanding total yields through palladium catalyzed intramolecular benzofuran formation. Restricted bond rotation of the phenoxy fragments leads to dyes 2 and 3, which absorb and fluoresce more intensely at longer wavelengths relative to the unconstrained dye 1. Reduction of the conformational flexibility in 2 and 3 leads to significantly higher fluorescence quantum yields compared to those of 1. X-ray diffraction analysis shows the progressively more extended planarity of the chromophore in line with the increasing conformational restriction in the series 1→2→3, which explains the larger red shifts of the absorption and emission spectra. These conclusions are confirmed by quantum chemical calculations of the lowest electronic excitations in 1-3 and dyes of related chemical structures. The effect of the molecular structure on the visible absorption and fluorescence emission properties of 1-3 has been examined as a function of solvent by means of the new, generalized treatment of the solvent effect (J. Phys. Chem. B 2009, 113, 5951-5960). Solvent polarizability is the primary factor responsible for the small solvent-dependent shifts of the visible absorption and fluorescence emission bands of these dyes. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

International audience; Cleavage reactions of 2,3-diamino-meso-tetraarylporphyrins and meso-tetraarylporphyrins fused to imidazole rings afforded secochlorins including stable free base derivatives.