Search

Time-dependent density functional theory (TDDFT) based approaches have been developed in recent years to model the excited-state properties and transition processes of the molecules in the gas-phase and in a condensed medium, such as in a solution and protein microenvironment or near semiconductor and metal surfaces. In the latter case, usually, classical embedding models have been adopted to account for the molecular environmental effects, leading to the multi-scale approaches of TDDFT/polarizable continuum model (PCM) and TDDFT/molecular mechanics (MM), where a molecular system of interest is designated as the quantum mechanical region and treated with TDDFT, while the environment is usually described using either a PCM or (non-polarizable or polarizable) MM force fields. In this Perspective, we briefly review these TDDFT-related multi-scale models with a specific emphasis on the implementation of analytical energy derivatives, such as the energy gradient and Hessian, the nonadiabatic coupling, the spin–orbit coupling, and the transition dipole moment as well as their nuclear derivatives for various radiative and radiativeless transition processes among electronic states. Three variations of the TDDFT method, the Tamm–Dancoff approximation to TDDFT, spin–flip DFT, and spin-adiabatic TDDFT, are discussed. Moreover, using a model system (pyridine–Ag20 complex), we emphasize that caution is needed to properly account for system–environment interactions within the TDDFT/MM models. Specifically, one should appropriately damp the electrostatic embedding potential from MM atoms and carefully tune the van der Waals interaction potential between the system and the environment. We also highlight the lack of proper treatment of charge transfer between the quantum mechanics and MM regions as well as the need for accelerated TDDFT modelings and interpretability, which calls for new method developments. [ABSTRACT FROM AUTHOR]

Computational modeling of plasmon-mediated molecular photophysical and photochemical behaviors can help us better understand and tune the bound molecular properties and reactivity and make better decisions to design and control nanostructures. However, computational investigations of coupled plasmon–molecule systems are challenging due to the lack of accurate and efficient protocols to simulate these systems. Here, we present a hybrid scheme by combining the real-time time-dependent density functional theory (RT-TDDFT) approach with the time-domain frequency dependent fluctuating charge (TD-ωFQ) model. At first, we transform ωFQ in the frequency-domain, an atomistic electromagnetic model for the plasmonic response of plasmonic metal nanoparticles (PMNPs), into the time-domain and derive its equation-of-motion formulation. The TD-ωFQ introduces the nonequilibrium plasmonic response of PMNPs and atomistic interactions to the electronic excitation of the quantum mechanical (QM) region. Then, we combine TD-ωFQ with RT-TDDFT. The derived RT-TDDFT/TD-ωFQ scheme allows us to effectively simulate the plasmon-mediated "real-time" electronic dynamics and even the coupled electron–nuclear dynamics by combining them with the nuclear dynamics approaches. As a first application of the RT-TDDFT/TD-ωFQ method, we study the nonradiative decay rate and plasmon-enhanced absorption spectra of two small molecules in the proximity of sodium MNPs. Thanks to the atomistic nature of the ωFQ model, the edge effect of MNP on absorption enhancement has also been investigated and unveiled. [ABSTRACT FROM AUTHOR]

In order to understand the mechanism of the electrochemical reduction of CO* on Cu(111), which competitively generates two intermediates, CHO* and COH*, we performed a first principles calculation on these two electrocatalytic reactions, including the solvent effect and imposing a constant potential. The transition states of the two reactions under constant potential conditions were located by the electrochemical nudged elastic band (eNEB) method and the charge effect in the two reactions was elucidated by charge correction in the constant potential model and Bader charge analysis. It was found that the two reactions have different potential dependencies and involve different degrees of partial charge transfer. In addition, we confirmed that the COH* reaction pathway exists only in a certain potential range when using the implicit solvent model. [ABSTRACT FROM AUTHOR]

The complex interplay between molecules and plasmonic metal nanoparticles (MNPs) presents a set of particular characteristics in absorption/scattering spectra such as excitonic splitting, asymmetric line shapes, plasmon-induced absorption enhancement and transparencies, etc. Although the MNP-molecule systems have been intensively investigated experimentally and theoretically, the construction of a theoretical framework which can produce all the disparate experimental observations and account for the electron-phonon (e-p) coupling is still in progress. Here, we present a theoretical approach which can account for both the plasmon-exciton coupling and the e-p interaction and produce all the spectral line shapes ranging from Fano antiresonance to Rabi splitting by simply tuning the coupling strength or plasmon damping rate. Additionally, we demonstrate the evolution of vibronic spectra and exciton dynamics with the coupling strength, plasmon damping rate, and detuning energy. It is found that the vibronic structures appearing in Rabi-like spectra are worse resolved, wider, and more largely shifted than those appearing in the Fano regime, attributed to the more significant deformation of the molecular vibrational wavepacket in the Rabi-like regime than that in the Fano regime as the molecular e-p interaction increases. The positive/negative value of detuning energy can induce different degrees of the vibrational wavepacket deformation and subsequently a different effect on the spectra in different coupling regimes. [ABSTRACT FROM AUTHOR]

It is of great importance and worthy of efforts to give a clear structure–property relationship and microscopic mechanism of fluorescence emitters with high quantum yield. In this work, we perform a detailed computational investigation to give an explanation to the high efficiency of a fluorescence emitter XBTD‐NPh based TADF sensitized fluorescence (TSF) OLEDs, and construct a symmetry structure DSBNA‐BTD. Theoretical calculations show that XBTD‐NPh is a long‐time phosphorescent material at 77 K and TADF is attributed to the RISC of T1 to S1 state. For DSBNA‐BTD, excitons arrived at T1 state comes to a large rate of nonradiatively path to the ground state, meaning it is may not be an efficient TADF molecule. For both molecules, the fast IC between T2 and T1 state results in that the hot exciton channel T1‐Tn‐S1 makes no contribution to the TADF. [ABSTRACT FROM AUTHOR]

The nonadiabatic phenomena, which are characterized by a strong coupling between electronic and nuclear motions, are ubiquitous. The nonadiabatic effect of the studied system can be significantly affected by the surrounding environment, such as solvents, in which such nonadiabatic process takes place. It is essential to develop the theoretical models to simulate these processes while accurately modeling the solvent environment. The time-dependent density functional theory (TDDFT) is currently the most efficient approach to describe the electronic structures and dynamics of complex systems, while the polarizable continuum model (PCM) represents one of the most successful examples among continuum solvation models. Here, we formulate the first-order derivative couplings (DCs) between the ground and excited states as well as between two excited states by utilizing time-independent equation of motion formalism within the framework of both linear response and spin flip formulations of TDDFT/CPCM (the conductor-like PCM), and implement the analytical DCs into the Q-CHEM electronic structure software package. The analytic implementation is validated by the comparison of the analytical and finite-difference results, and reproducing geometric phase effect in the protonated formaldimine test case. Taking 4-(N,N-dimethylamino)benzonitrile and uracil in the gas phase and solution as an example, we demonstrate that the solvent effect is essential not only for the excitation energies of the low-lying excited-states but also for the DCs between these states. Finally, we calculate the internal conversion rate of benzophenone in a solvent with DC being used. The current implementation of analytical DCs together with the existing analytical gradient and Hessian of TDDFT/PCM excited states allows one to study the nonadiabatic effects of relatively large systems in solutions with low computational cost. [ABSTRACT FROM AUTHOR]

The paper presents the formalism, implementation, and performance of the analytical approach for the excited-state Hessian in the time-dependent density functional theory (TDDFT) that extends our previous work [J. Liu and W. Z. Liang, J. Chem. Phys. 135, 014113 (2011)] on the analytical Hessian in TDDFT within Tamm-Dancoff approximation (TDA) to full TDDFT. In contrast to TDA-TDDFT, an appreciable advantage of full TDDFT is that it maintains the oscillator strength sum rule, and therefore yields more precise results for the oscillator strength and other related physical quantities. For the excited-state harmonic vibrational frequency calculation, however, full TDDFT does not seem to be advantageous since the numerical tests demonstrate that the accuracy of TDDFT with and without TDA are comparable to each other. As a common practice, the computed harmonic vibrational frequencies are scaled by a suitable scale factor to yield good agreement with the experimental fundamental frequencies. Here we apply both the optimized ground-state and excited-state scale factors to scale the calculated excited-state harmonic frequencies and find that the scaling decreases the root-mean-square errors. The optimized scale factors derived from the excited-state calculations are slightly smaller than those from the ground-state calculations. [ABSTRACT FROM AUTHOR]

A method in time domain is proposed to investigate resonance Raman spectra of absorbed molecules on semiconductor surfaces. The charge transfer at the molecule-surface interface is incorporated with the use of an Anderson-Newns type Hamiltonian, where the surface continuum state is dealt with an expansion of Legendre polynomials for fast numerical convergence. From a model test, it is found that the intensities of Raman modes in the sole molecule generally decrease as the molecule-surface interaction is switched on, except that the energy gaps between the molecular excited state and the bottom of the band are at special values. New Raman peaks which are not observed in the sole molecule, however, appear and are greatly enhanced. The enhancement depends on the electronic coupling and the energy gap. It is also highly sensitive to the mode-specific reorganization energy in the charge transfer state, and a thousand times enhancement can be obtained at a certain reorganization energy. The corresponding electron dynamics is revealed by the population decay from the absorbed molecule. [ABSTRACT FROM AUTHOR]

We present the analytical expression and computer implementation for the second-order energy derivatives of the electronic excited state with respect to the nuclear coordinates in the time-dependent density functional theory (TDDFT) with Gaussian atomic orbital basis sets. Here, the Tamm-Dancoff approximation to the full TDDFT is adopted, and therefore the formulation process of TDDFT excited-state Hessian is similar to that of configuration interaction singles (CIS) Hessian. However, due to the replacement of the Hartree-Fock exchange integrals in CIS with the exchange-correlation kernels in TDDFT, many quantitative changes in the derived equations are arisen. The replacement also causes additional technical difficulties associated with the calculation of a large number of multiple-order functional derivatives with respect to the density variables and the nuclear coordinates. Numerical tests on a set of test molecules are performed. The simulated excited-state vibrational frequencies by the analytical Hessian approach are compared with those computed by CIS and the finite-difference method. It is found that the analytical Hessian method is superior to the finite-difference method in terms of the computational accuracy and efficiency. The numerical differentiation can be difficult due to root flipping for excited states that are close in energy. TDDFT yields more exact excited-state vibrational frequencies than CIS, which usually overestimates the values. [ABSTRACT FROM AUTHOR]

A new formulation of the diagonalization step in self-consistent-field (SCF) electronic structure calculations is presented. It exactly replaces the diagonalization of the effective Hamiltonian with the solution of a set of second order nonlinear equations. The density matrix and/or the new set of occupied orbitals can be directly obtained from the resulting solution. This formulation may offer interesting possibilities for new approaches to efficient SCF calculations. The working equations can be derived either from energy minimization with respect to a Cayley-type parametrization of a unitary matrix, or from a similarity transformation approach. [ABSTRACT FROM AUTHOR]

A variety of chemical systems exhibit multiple reaction pathways that adjoin to a common reactant state. In fact, any reaction producing side products or proceeding via a stable intermediate involves a species possessing at least two reaction pathways. Despite improvements in ab initio transition-state search algorithms it remains difficult to detect multiple reaction pathways. Typically, multiple reaction pathways can only be detected by intuitively varying the initial point in the transition-state search trajectory. This reliance on intuition limits the ability to discover new and unexpected chemistry using ab initio methods. This paper proposes a systematic and intuition-free method for biasing a transition-state search to identify multiple reaction pathways originating from a common reactant state. The method allows the successive location of transition states, with each successful search contributing to a cumulative bias potential for the following search. The method is applicable to all psuedo-Newton-Raphson-type transition-state searches. The procedure was tested for a model potential energy surface and for the thermal rearrangement of trans-1,4-dimethylcyclobutene. In the latter case, four reaction pathways were discovered: two exothermic conrotatory ring openings leading to hexadienes, an endothermic methyl migration pathway leading to a carbene, and an exothermic rearrangement leading to 3-methyl-1,4-pentadiene. In accordance with experiment, the calculations predict that the conrotatory pathway leading to trans,trans-2,4-hexadiene is the kinetically dominant pathway. The methodology was also used to compute selectivities for competitive pathways producing trans and cis triflouropentadiene products in the thermal rearrangement of 3-triflouromethyl-cyclobutene. Again, results were in accord with experimental observations. [ABSTRACT FROM AUTHOR]

We performed a first-principles systematic study on the fitness of two tricyclic donors (acridine and benzazasiline) interacting with five acceptors (triazine or triphenylborane-based) within the donor-acceptor-donor (D-A-D) framework for the potential application in organic light-emitting diodes (OLEDs) as thermally activated delayed fluorescence (TADF) emitters. Three types of compounds (D1-A-D1 (I), D2-A-D2 (II), and D1-A-D2 (III) were thus constructed to investigate the substitution pattern which can exhibit good TADF performance. We found that: by incorporating into the D-A-D frameworks and adopting an appropriate donor/acceptor combination, the studied compounds can bear rather small singlet-triplet gaps of ∼ 0.02 eV, and the emission energy can span a large space in (deep-)blue region ( 2.62 ∼ 3.13 eV); the molecular symmetry, in addition to the character of donors, control the properties of excited states, and acridine is more easily to be excited compared to benzazasiline. The symmetric setup (types I and II) is more suitable than asymmetric counterpart (type III) for optimal optoelectric properties. Accompanied with estimation of emission energy and rate constant, this study suggests that benzazasiline donor can serve as a versatile structural unit to combine with triphenylborane-based acceptor cores for constructing deep-blue D-A-D TADF emitters. [ABSTRACT FROM AUTHOR]

In this review, we summarize the computationally efficient time-dependent approaches to calculating the vibronic spectra including one-photon/two-photon absorption (OPA/TPA), emission, circular dichroism (CD), and resonance Raman/hyper-Raman scattering (RRS/RHRS) spectra with inclusion of the mode-mixing, Frank-Condon (FC) and Herzberg-Teller (HT) effects. At first, a unified dependency of spectral differential cross sections (SDCSs) on a generalized linear polarizability is derived in view of the relationship between SDCSs and the linear or nonlinear polarizabilities. Then, the Green's function technique is adopted to calculate the polarizability to avoid the tedious summation over the large number of vibrational states. To demonstrate the computational accuracy and efficiency, we apply the generalized time-dependent approaches to calculate the OPA(E)/TPA, RRS, and RHRS spectra of a series of radicals and organic molecules. The computational accuracy is demonstrated by a close comparison between the simulated spectra and the available experimental data. In the spectral calculations, we apply our recently developed analytical energy-derivative approaches for the excited states within the framework of time-dependent density functional theory (TDDFT) to calculate the electronic-structure parameters which enter the expressions of SDCSs, such as the excited-state geometries, energy gradient, harmonic vibrational frequencies, the geometrical derivatives of transition dipole moments, and so forth. It is found that the integrated approach which combines the time-dependent approach to SDCSs with the analytical energy-derivative approaches for TDDFT excited-state structure parameters breaks the bottlenecks of vibronic spectroscopy calculation down. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Density functional theory and time-dependent density functional theory with hybrid functional B3LYP are employed to investigate several physical and chemical properties of N-methyle-3,4-fulleropyrrolidine (NMFP), including geometry, electron population, infrared (IR), Raman and electronic absorption spectra. The analysis of the natural bond orbital (NBO) suggests that there are about 0.16 electrons transferred from the moiety –C3NH7 of NMFP to fullerene cage. The strongest IR and Raman spectra are from different modes with frequencies of 2955 and 1490cm−1, respectively. The calculated isotropic polarizability, polarizability anisotropy invariant and hyperpolarizability are 521.6, 65.3 and −68 (a.u.), respectively. The calculated electronic absorption spectra agree well with the experimental measurement. The solvent cyclohexane did not significantly affect the overall spectral shape but the absorption intensity and low-energy-band locations. The first absorption band in visible region comes from transitions, and the bands near 437 and 451 nm are both related to the ligand-to-fullerene charge transfer processes. The second absorption band in near-UV region is dominated by typical transitions. [Copyright &y& Elsevier]

Abstract: We present systematically theoretical investigations on electronic and optical properties of quasi-one-dimensional (1D) all-carbon materials: C60 polymers (CP), periodic peanut-shaped fulleriods (PPSF) and armchair (5,5) carbon nanotubes (CNTs) to understand structure–property relationships. Their electronic structures and optical absorption spectra are calculated by the first-principles density functional theory and the random phase approximation (RPA). It is found that the system structures and sizes play a vital role on their physical properties so that three systems show distinctively different electronic and optical behaviors. CP and PPSF exhibit finite energy-band gaps while (5,5) CNTs are found metallic. Unlike C60 polymers and PPSF, whose optical properties are converged with a few of C60 units, the optical spectra of CNTs depend very much on the tube length and the converged optical properties of CNTs are not observed even for the tube as long as 100Å due to the overall delocalized π-electrons. The optical properties of infinite long systems have been predicted by the finite-size calculations. The relation between the geometrical structures and electronic properties have been quantitatively established. [Copyright &y& Elsevier]

It has been widely recognized that plasmonic metal nanoparticles (MNPs) can enhance the power convention efficiency (PCE) of dye-sensitized solar cells (DSSCs). This enhancement is ascribed to the combined effects of plasmon decay, scattering, near-field enhancement, and exciting charge carriers in semiconductors through plasmon-induced resonance energy transfer (PIRET) and hot electron injection (HEI). PIRET and HEI processes appeared between MNPs, and semiconductors have been intensively investigated; however, it is not clear how the collaborative effect of PIRET and photon-induced direct and indirect electron transfer (PICT) occurred between plasmonic metals and dyes, and the interference of different charge separation channels (CSCs) starting from PIRET and PICT affects the PCE of DSSCs. This work aims to address these issues. We apply a model Hamiltonian method, which obviously includes both PIRET and PICT processes from Au MNP to dye molecules and incorporates the dye's electron-phonon interaction, to investigate the carrier dynamics. It is found that PIRET deforms the wavepacket dynamics of the molecular excited state and results in ten-fold enhancement of dye absorption. MNPs augment light absorption and increase the electron density in empty molecular orbitals of the dye molecule. Consequently, this enhances the interfacial charge separation. Furthermore, we observed the interference behavior of two CSCs and gave a full-scale insight into the correlation between the constructive/destructive interference and the electronic-state properties as well as carrier-phonon interactions. This work provides a theoretical guidance to optimize DSSCs. [ABSTRACT FROM AUTHOR]

Fast and effective algorithms are discussed for resumming matrix polynomials and Chebyshev matrix polynomials. These algorithms lead to a significant speed-up in computer time by reducing the number of matrix multiplications required to roughly twice the square root of the degree of the polynomial. A few numerical tests are presented, showing that evaluation of matrix functions via polynomial expansions can be preferable when the matrix is sparse and these fast resummation algorithms are employed. [Copyright &y& Elsevier]

A method to calculate the circular dichroism (CD) spectra of macromolecules has been developed. The intermediate neglect of differential overlap technique for spectroscopy (INDO/S) semiempirical Hamiltonian and the full multipole expansion is adopted. The method has been employed to calculate the CD spectra of pentahelicene, and excellent agreement with the experimental result is obtained. Combined with the localized-density-matrix (LDM) method, the new method can be employed to calculate the CD spectra of large molecules. [Copyright &y& Elsevier]

A fast method is described for evaluating multiple exchange matrices in a Gaussian atomic orbital basis. For insulators, it is asymptotically linear scaling, and is a generalization of the linear scaling exchange (LinK) method, which was formulated for a single exchange matrix [J. Chem. Phys. 109 (1998) 1663]. It is employed to evaluate exchange-type contractions of all derivative density matrices with two-electron integrals for a series of linear alkanes, linear polyacenes, and water clusters using STO-3G, 3-21G, and 6-31G* basis sets. Significant computational savings are obtained for molecules with as few as 10 non-hydrogen atoms. [Copyright &y& Elsevier]

This work extends our previous works [J. Liu and W. Z. Liang, J. Chem. Phys. 135, 014113 (2011); J. Liu and W. Z. Liang, J. Chem. Phys. 135, 184111 (2011)] on analytical excited-state Hessian within the framework of time-dependent density functional theory (TDDFT) to couple with a conductor-like polarizable continuum model (CPCM). The formalism, implementation, and application of analytical first and second energy derivatives of TDDFT/CPCM excited state with respect to the nuclear and electric perturbations are presented. Their performances are demonstrated by the calculations of excitation energies, excited-state geometries, and harmonic vibrational frequencies for a number of benchmark systems. The calculated results are in good agreement with the corresponding experimental data or other theoretical calculations, indicating the reliability of the current computer implementation of the developed algorithms. Then we made some preliminary applications to calculate the resonant Raman spectrum of 4-hydroxybenzylidene-2,3-dimethyl-imidazolinone in ethanol solution and the infrared spectra of ground and excited states of 9-fluorenone in methanol solution. [ABSTRACT FROM AUTHOR]

Absorption spectrum of recently discovered single-walled 4 Å carbon nanotubes is measured. The semiempirical PM3 localized-density-matrix method is employed to evaluate the absorption spectra of three possible 4 Å single-walled carbon nanotubes, (3,3), (4,2), and (5,0). Both experimental and calculated results reveal that these nanotubes have finite optical gaps and strong anisotropic optical responses. When the electric field is perpendicular to the nanotubes, they are transparent to visible lights; and this is confirmed and explained by the calculations. Compared to the measured absorption spectrum, calculated absorption spectra are used to determine the chirality of the nanotubes synthesized in the channels of porous zeolites. [ABSTRACT FROM AUTHOR]

The linear scaling localized-density-matrix (LDM) method is generalized to calculate the nonlinear optical responses of large polyacetylene oligomers. The ground state reduced single-electron density matrix is initialized by the divide-and-conquer approach and is obtained subsequently using the LDM method. The third-harmonic generation spectra of large oligomers are calculated. The saturation of off-resonant second hyperpolarizability χ[sup (3)](0) has been reinvestigated, and the value of χ[sup (3)](0) is found to depend mainly on the optical gap and the number of double bonds. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This work is devoted to deriving and implementing analytic second- and third-order energy derivatives with respect to the nuclear coordinates and external electric field within the framework of the hybrid quantum mechanics/molecular mechanics method with induced charges and dipoles (QM/DIM). Using these analytic energy derivatives, one can efficiently compute the harmonic vibrational frequencies, infrared (IR) and Raman scattering (RS) spectra of the molecule in the proximity of noble metal clusters/nanoparticles. The validity and accuracy of these analytic implementations are demonstrated by the comparison of results obtained by the finite-difference method and the analytic approaches and by the full QM and QM/DIM calculations. The complexes formed by pyridine and two sizes of gold clusters (Au18 and Au32) at varying intersystem distances of 3, 4, and 5 Å are used as the test systems, and Raman spectra of 4,4′-bipyridine in the proximity of Au2057 and Ag2057 metal nanoparticles (MNP) are calculated by the QM/DIM method and compared with experimental results as well. We find that the QM/DIM model can well reproduce the IR spectra obtained from full QM calculations for all the configurations, while although it properly enhances some of the vibrational modes, it artificially overestimates RS spectral intensities of several modes for the systems with very short intersystem distance. We show that this could be improved, however, by incorporating the hyperpolarizability of the gold metal cluster in the evaluation of RS intensities. Additionally, we address the potential impact of charge migration between the adsorbate and MNPs. [ABSTRACT FROM AUTHOR]

We comment on an excited‐state localization method recently proposed by Blanc et al. (J. Comput. Chem. 2023, 44, 105). Elaborate comparisons are made to demonstrate that their method is a less‐comprehensive version of the diabatization method proposed by us 2 years earlier (J. Phys. Chem. Lett. 2021, 12, 1032). [ABSTRACT FROM AUTHOR]

The donor‐acceptor interface plays a critically important role in determining the power conversion efficiency of organic solar cells via controlling charge separation (CS) and recombination (CR) processes. Here, we combine the electronic structure calculations with electron transfer rate theory to clarify the CS and CR processes in ThQs‐C60/PDIxCN2 donor‐acceptor complexes. The results reveal that in ThQs‐PDIxCN2 the CS comes from both the dissociations of photo‐induced singlet exciton and singlet fission‐induced triplet exciton with a high efficiency, whereas in ThQs‐C60 only the singlet exciton dissociation can take place because the triplet exciton lies below the charge‐transfer exciton. However, very high CR rates in ThQs‐PDIxCN2 obliterate the benefit of fast CS, inversely leading to the ThQ‐C60 complex with a better cell efficiency. The present results are consistent with experimental observation and may furnish a possible patten to improve the overall conversion efficiency. © 2018 Wiley Periodicals, Inc. The charge separation (CS) and recombination (CR) processes in the donor‐acceptor interface play a critically important role in the determination of power conversion efficiency of organic solar cells. This work performs a theoretical calculation on CS and CR rates of ThQs‐C60/PDIxCN2 complexes and offers a theoretical explanation to the experimental observation. [ABSTRACT FROM AUTHOR]

Both the vibrationally resolved and statistically averaged one-photon absorption (OPA) and two-photon absorption (TPA) spectra of the anionic form of chromophore (AC) in its micro-environment of yellow fluorescent protein (YFP) Citrine have been calculated. The result comparison has been made with those of the AC model compounds in vacuo and methanol solution, which allows us to allocate the individual contribution of the intramolecular electron-vibrational coupling, the electrostatic π-stacking interaction between Tyr203 and AC, and the interaction between AC and its micro-environment to the spectra. The results reveal that the non-Condon vibronic coupling effect is responsible for the blue shift of TPA absorption maximum compared with its OPA counterpart corresponding to S0 → S1, and that the π-stacking interaction between Tyr203 and AC alters the relative intensities of TPA maxima, which further enhances the higher-energy vibronic peaks and weakens the lowest-energy peak. The statically averaged OPA and TPA spectra calculated by quantum mechanics/molecular mechanics (QM/MM) methods based on Born-Oppenheimer molecular dynamics simulation largely deviate the experimental spectral lineshapes, which further verifies the significant contribution of non-Condon vibronic coupling effect on the spectra. The interaction of individual amino acid residue or water close to AC+Tyr203 has different effects on the spectra, which may increase/decrease the excitation energy depending on its position and electronic property. [ABSTRACT FROM AUTHOR]

The spectral densities of diagonal and nondiagonal exciton-phonon (e-p) coupling for tetracene crystal have been calculated by the harmonic oscillator (HO) model and ground-state MD-based approaches. We find that classical MD-based approaches overestimate the coupling of exciton with high-frequency vibrational modes and predict the strongest e-p coupling appeared above 1500 cm −1 whereas HO model and AIMD-based approach predict it appeared at ∼ 1400 cm −1 . Additionally, the calculated spectral densities of nondiagonal e-p coupling for three different dimers show that they are continuously distributed in the range of 0–150 cm −1 and are 2–3 order of magnitude smaller than the maxima of diagonal e-p coupling. [ABSTRACT FROM AUTHOR]

The vibrationally resolved absorption spectra of zinc phthalocyanine (ZnPc) aggregates (up to 70 monomers) are explored using the non-Markovian stochastic Schrödinger equation. Various types of local excitations, charge-transfer (CT) excitations, and exciton–phonon couplings are explicitly included in a comprehensive model Hamiltonian, which is parameterized by first-principles calculations. The absorption spectral simulations clarify that the two absorption bands in the Q-band region observed in experiments can be assigned to the contribution from the CT-mediated interactions, rather than the mixtures of different-type aggregates, as prevailingly assumed. Furthermore, the relative intensities of the two bands are found to be closely related to the intermolecular distance and molecular number in a ZnPc aggregate. From the investigation of the decoherence process after optical excitation, it is found that CT states can induce coherence regeneration as the time scale of charge separation is much faster than that of the vibration-induced decoherence. However, they would instead boost the decoherence process as the two time scales become comparable. The two different effects of CT states may suggest a novel way to regulate the decoherence process in excitation energy relaxation. [ABSTRACT FROM AUTHOR]

The nonlinear optical properties of hybrid systems composed of a silver nanosphere and an open-ended finite-sized armchair single-walled carbon nanotube (SWCNT) are systematically investigated by the hybrid time-dependent Hartree–Fock (TDHF)/finite difference time domain (FDTD) approach, which combines the real-time TDHF approach for the molecular electronic dynamics with the classical computational electrodynamics approach, the FDTD, for solving Maxwell's equations. The high order harmonic generation (HHG) spectra of SWCNTs are studied as a function of the intensity (I0) and frequency (ω0) of the incident field, and SWCNTs length as well. It is found that the near field generated by a Ag nanoparticle has an overall enhancement to the molecular HHG in all the energy range, and it extends the HHG spectra to high energy. The inhomogeneity of the near field results in the appearance of even-order harmonics, and their corresponding spectral intensities are sensitive to ω0, therefore the near field's gradient. When ω0 is far away from the frequency of plasmon resonance of the silver nanosphere (ωc), the interference between the incident and scattering light beams extends the spectral range and makes the HHG spectra more sensitive to I0, while at ω0 = ωc, the impact of the interference on the spectra is negligible. [ABSTRACT FROM AUTHOR]

Natural light‐harvesting (LH) systems can divide identical dyes into unequal aggregate states, thereby achieving intelligent "allocation of labor". From a synthetic point of view, the construction of such kinds of unequal and integrated systems without the help of proteinaceous scaffolding is challenging. Here, we show that four octatetrayne‐bridged ortho‐perylene diimide (PDI) dyads (POPs) self‐assemble into a quadruple assembly (POP)4 both in solution and in the solid state. The two identical PDI units in each POP are compartmentalized into weakly coupled PDIs (P520) and closely stacked PDIs (P550) in (POP)4. The two extreme pools of PDI chromophores were unambiguously confirmed by single‐crystal X‐ray crystallography and NMR spectroscopy. To interpret the formation of the discrete quadruple assembly, we also developed a two‐step cooperative model. Quantum‐chemical calculations indicate the existence of multiple couplings within and across P520 and P550, which can satisfactorily describe the photophysical properties of the unequal quadruple assembly. This finding is expected to help advance the rational design of dye stacks to emulate functions of natural LH systems. [ABSTRACT FROM AUTHOR]

Natural light‐harvesting (LH) systems can divide identical dyes into unequal aggregate states, thereby achieving intelligent "allocation of labor". From a synthetic point of view, the construction of such kinds of unequal and integrated systems without the help of proteinaceous scaffolding is challenging. Here, we show that four octatetrayne‐bridged ortho‐perylene diimide (PDI) dyads (POPs) self‐assemble into a quadruple assembly (POP)4 both in solution and in the solid state. The two identical PDI units in each POP are compartmentalized into weakly coupled PDIs (P520) and closely stacked PDIs (P550) in (POP)4. The two extreme pools of PDI chromophores were unambiguously confirmed by single‐crystal X‐ray crystallography and NMR spectroscopy. To interpret the formation of the discrete quadruple assembly, we also developed a two‐step cooperative model. Quantum‐chemical calculations indicate the existence of multiple couplings within and across P520 and P550, which can satisfactorily describe the photophysical properties of the unequal quadruple assembly. This finding is expected to help advance the rational design of dye stacks to emulate functions of natural LH systems. [ABSTRACT FROM AUTHOR]

Nowadays, it is an attractive strategy to promote the efficiency of photocatalytic reactions by introducing the heterojunctions. Bismuth vanadate (BiVO4), one of the promising non-titania-based visible light-driven semiconductor photocatalysts, possesses three different crystal phases which can transform from one phase to another under appropriate conditions. The heterophase junction built by the monoclinic scheelite (s-m) and tetragonal zircon (z-t) phase BiVO4 has been demonstrated to have high photocatalytic activity than the single-phase BiVO4. Here we presented a step-by-step protocol based on the first-principles density functional theory calculations to explore the origin of high photocatalytic activity existed in BiVO4 heterojunction. The mixed-phase geometrical structures, density of states, electrostatic potential, electron localization function and band offsets of optimal interface have been calculated. For the heterojunction, the calculated valence band maximum and conduction band minimum of z-t BiVO4 are 0.29 and 0.32 eV above those of s-m BiVO4, respectively, indicating that the presence of interface in monoclinic/tetragonal heterophase provides a spatial condition for charge carrier separation and promotes the separation of photoinduced electron–hole pairs. Further calculations reveal that the direction of electron migration across the phase boundary is from z-t to s-m, consistent with the experimental observation. [ABSTRACT FROM AUTHOR]

Abstract: A simplified approach for computing the electronic coupling of nonradiative excitation-energy transfer is proposed by following Scholes et al.’s construction on the initial and final states [G.D. Scholes, R.D. Harcourt, K.P. Ghiggino, J. Chem. Phys. 102 (1995) 9574]. The simplification is realized through defining a set of orthogonalized localized MOs, which include the polarization effect of the charge densities. The method allows calculating the coupling of both the singlet-to-singlet and triplet-to-triplet energy transfer. Numerical tests are performed for a few of dimers with different intermolecular orientations, and the results demonstrate that Coulomb term are the major contribution to the coupling of singlet-to-singlet energy transfer whereas in the case of triplet-to-triplet energy transfer, the dominant effect is arisen from the intermolecular charge-transfer states. The present application is on the Hartree–Fock level. However, the correlated wavefunctions which are normally expanded in terms of the determinant wavefunctions can be employed in the similar way. [Copyright &y& Elsevier]

Abstract: The O-trans and O-cis rotamers in the electronic ground states and the low-lying excited states of 2-, 3- and 4-pyridinecarboxaldehydes have been investigated theoretically. The detailed studies of the electronic excited states reveal that the lowest triplet states (T1) and singlet states (S1) correspond to the nπ* excitations and all T1 states mainly come from the electron transition of the lone-pair electrons located on the carbonyl oxygen (n(O)) to π* orbitals and the electron transition of S1 states depends on the geometrical conformations. The mechanism has been further confirmed by the phosphorescence and fluorescence obtained from the transition dipole auto-correlation function approach. In addition, the calculated spectra agree well with the available experimental data. [Copyright &y& Elsevier]

Stepwise ring closing processes of platinum(II) alkynyl arkynyl bridged DTEs (OO→OC→CC) were studied theoretically with density functional theory method in this work for better understanding the Pt(II) alkynyl coordination effect on the photophysical and photochemical properties of dithienylethene (DTE). It is observed that the absorption spectrum of OO complex is red-shifted compared with that of ring-opened DTE monomer because of the decreased HOMO-LUMO gap energy. The first S 0 →S 1 absorption of OC is red shifted than that of OO and is blue shifted than that of CC complex because of the increased conjugation of the ring-closed DTE moiety. In addition, potential energy surface (PSE) studies show that the energy barrier for the ring-closing process in the ground state of Pt(II) complex is smaller than that of the isolated DTE monomer and the isomerization process is changed from endothermic to exothermic reaction. Moreover, the energy barrier for the first ring-closing process is a little larger than the second ring-closing process involved in the DTE moieties. More important, similar with that in the DTE monomers, the ring closing processes in the ionic and triplet states of Pt(II) complexes is easier than that in the neutral case. [ABSTRACT FROM AUTHOR]

Vibrationally resolved fluorescence spectra of the β-hairpintrpzip2 peptide at two temperatures as well as during a T-jump unfolding process are simulated on the basis of a combinationof Markov state models and quantum chemistry schemes. The broad asymmetricspectral line shape feature is reproduced by considering the exciton–phononcouplings. The temperature dependent red shift observed in the experimenthas been attributed to the state population changes of specific chromophores.Through further theoretical study, it is found that both the environment'selectric field and the chromophores’ geometry distortions areresponsible for tryptophan fluorescence shift. [ABSTRACT FROM AUTHOR]

• An innovative aptamer SERS biosensor for highly sensitive protein biomarker detection was presented. • The biosensor contains SERS tags and novel magnetic capture substrates. • Aptamers against CRP were modified on both SERS tag and magnetic capture substrate for specific recognition. • This method exhibits excellent selectivity and specificity and displays high accuracy in actual human serum samples. • This strategy can be extended to the detection of other biomarkers and hold great promise in the clinical diagnosis. The design of a rapid, simple, and ultrasensitive detection platform of protein biomarkers has become an urgent need in early diagnosis and treatment. Surface-enhanced Raman scattering (SERS) technology, with the unique advantages of ultra-sensitivity and fingerprint recognition, has attracted much attention in biomarker detection. An innovative aptamer SERS biosensor for highly sensitive protein biomarker detection was presented. This biosensor contains a SERS tag (reporter-labeled Au nano-bridged nanogaps particles, Au NNPs) and novel magnetic capture substrate (Ag-coated Fe 3 O 4 -Au NPs, Ag MNPs). C-reactive protein (CRP), a representative biomarker for diagnosing, was used to assess the SERS performance of this biosensor. Aptamers against CRP were modified on both SERS tag and magnetic capture substrate for specific recognition by Au NNPs-CRP-Ag MNPs sandwich assay. This strategy achieved sensitive detection of CRP with a limit of detection (LOD) of 10 fM (1.14 pg/mL), and is much lower than reported analytical methods. Besides, this method exhibits excellent selectivity and specificity for CRP under the interference of other proteins and displays high accuracy in the detection of actual human serum samples. This proposed detection strategy can be extended to the sensitive detection of other biomarker proteins and hold great promise in the clinical diagnosis of diseases. [ABSTRACT FROM AUTHOR]

In the modeling of spin‐crossing reactions, it has become popular to directly explore the spin‐adiabatic surfaces. Specifically, through constructing spin‐adiabatic states from a two‐state Hamiltonian (with spin‐orbit coupling matrix elements) at each geometry, one can readily employ advanced geometry optimization algorithms to acquire a "transition state" structure, where the spin crossing occurs. In this work, we report the implementation of a fully‐variational spin‐adiabatic approach based on Kohn‐Sham density functional theory spin states (sharing the same set of molecular orbitals) and the Breit‐Pauli one‐electron spin‐orbit operator. For three model spin‐crossing reactions (predissociation of N2O, singlet‐triplet conversion in CH2, and CO addition to Fe(CO)4), the spin‐crossing points were obtained. Our results also indicated the Breit‐Pauli one‐electron spin‐orbit coupling can vary significantly along the reaction pathway on the spin‐adiabatic energy surface. On the other hand, due to the restriction that low‐spin and high‐spin states share the same set of molecular orbitals, the acquired spin‐adiabatic energy surface shows a cusp (ie, a first‐order discontinuity) at the crossing point, which prevents the use of standard geometry optimization algorithms to pinpoint the crossing point. An extension with this restriction removed is being developed to achieve the smoothness of spin‐adiabatic surfaces. [ABSTRACT FROM AUTHOR]