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The vibrationally resolved spectral method and quantum chemical calculations are employed to reveal the structural and spectral properties of Coumarin 343 (C343), an ideal candidate for organic dye photosensitizers, in vacuum and solution. The results manifest that the ground-state energies are dominantly determined by different placements of hydrogen atom in carboxylic group of C343 conformations. Compared to those in vacuum, the electronic absorption spectra in methanol solvent show a hyperchromic property together with the redshift and blueshift for the neutral C343 isomers and their deprotonated anions, respectively. From the absorption, emission, and resonance Raman spectra, it is found that the maximal absorption and emission come from low-frequency modes whereas the high-frequency modes have high Raman activities. The detailed spectra are further analyzed for the identification of the conformers and understanding the potential charge transfer mechanism in their photovoltaic applications. [ABSTRACT FROM AUTHOR]

On the reported TCP‐OH (See Scheme 1), other two star‐shaped molecules are theoretically designed by replacement of side group of TCP‐OH by N,N‐di(4‐methoxyphenyl)aniline for TPAP‐OH and oxygen‐bridged triarylamine for TBOPP‐OH. The core group, phenol, is kept in three molecules. Their potential to be hole transport material in perovskite solar cells without dopants is evaluated by multiscale simulations. The properties of isolated molecules are estimated by the frontier molecular orbital, absorption spectrum, and hole mobility. After that, the HTM@CH3NH3PbI3 adsorbed system is studied to consider the influence of adsorption on HTM performance. Besides the primary judgment, the glass transition temperature is also simulated to determine the stability of amorphous film. Not only the chemical stability is evaluated but also the amorphous film stability is considered. The latter is almost neglected in previous theoretical studies to evaluate the properties of HTMs. The performance of a designed molecule is evaluated from both the isolated molecules and HTM@CH3NH3PbI3 adsorbed system including aforementioned items, which is favorable to build reliable structure‐property relationship. [ABSTRACT FROM AUTHOR]

Inverted perovskite solar cells (PSCs) have attracted much attention due to their low-temperature and solution-based process. Electron transport layers are important components in inverted PSCs. Non-fullerene n-type organic small molecules seem to be more attractive as electron transport layers, because their structures are easy to be synthesised and modified. In this paper, density functional theory and semi-classical Marcus electron transfer theory were used to explore the electron transport properties in three azaacene derivatives, including one experimentally reported molecule, 1,4,9,16-tetrakis((triisopropylsilyl)ethynyl)quinoxalino[2‴,3‴:4″,5″]cyclopenta[1″,2″,3″:5′,6′]acenaphtho[1′,2′:5,6]pyrazino[2,3-b]phenazine (1), and two theoretically designed molecules (2 and 3). Compound 2 is formed by substituting i-Pr groups in compound 1 with H atoms, which is designed to evaluate the effect of i-Pr groups on the electron transport properties. Compound 3 is designed by adding one more benzopyrazine group to the conjugation structure of compound 1. It shows that i-Pr group can increase HOMO and LUMO energy levels and improve solubility in organic solvent and hydrophobicity. Enlarging conjugation can not only decrease LUMO energy level and electron reorganisation energy, but also can increase solubility and electron mobility. So our designed compound 3 is expected to be a potential electron transport material in inverted PSCs. [ABSTRACT FROM AUTHOR]

Discotic liquid crystal (DLC) materials have attracted considerable attention mainly due to their high charge carrier mobilities in quasi‐one‐dimensional columns. In this article, five hexaazatrinaphthylene‐based DLC molecules were investigated theoretically, and their frontier molecular orbital energy levels, crystal structures, and electron/hole drift mobilities were calculated by combination of density functional theory (DFT) and semiclassical Marcus charge transfer theory. The systems studied in this work include three experimentally reported molecules (1, 2, and 3) and two theoretically designed molecules (4 and 5). Compared with the 1–3 compounds, 4 and 5 have three more extended benzene rings in the π‐conjugated core. The present results show that the orders of the frontier molecular orbital energy levels and electron drift mobilities agree very well with the experiment. For 4 and 5, the electron/hole reorganization energies are lower than those of compounds 1–3. Furthermore, the calculated electron/hole transfer integral of 5 is the largest among all the five systems, leading to the highest electron and hole mobilities. In addition, the hydrophobicity and solubility were also evaluated by DFT, indicating that compound 5 has good hydrophobicity and good solubility in trichloromethane. As a result, it is expected that compound 5 can be a potential charge transport material in electronic and optoelectronic devices. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

It is well known that interfacial structures and charge transfer in dye-sensitized solar cells are extremely important for the enhancement of cell efficiency. Here, the normal Raman spectra (NRS) and resonance Raman spectra (RRS) of a C343-sensitized TiO2 cluster (Ti9O18) are theoretically predicted from combined electronic structure calculations and a vibrationally-resolved spectral method to reveal the relationship between interfacial geometries and excited-state dynamics. The results show that although the NRS of free C343 and the C343–TiO2 cluster correspond to the vibrational motions of C343 in a high frequency domain, their mode frequencies show obvious differences due to the interaction of the TiO2 cluster on C343, and several new Raman active fingerprint modes, such as bidentate chelating bonding modes, can be used to determine interfacial geometries. However, the resonance Raman activities of low-frequency modes are significantly enhanced and several modes from the TiO2 cluster can be observed, consistent with experimental measurements. Furthermore, the RRS from a locally excited state and a charge transfer state of C343–TiO2 are dramatically different, for instance, new Raman active modes with 1212 cm−1, 1560 cm−1 and 1602 cm−1, corresponding to the motions of CH2 rocking, C=C/C–N/C=O stretching and C=O/C=C stretching, appear from the charge transfer state. The obtained information on mode-specific reorganization energies from these excited states is greatly helpful to understand and control interfacial electron transfer. [ABSTRACT FROM AUTHOR]

Abstract: Optimized geometries of small carbon clusters C3Cl and its ions in their ground and selected excited states have been obtained by CASSCF approach. The vertical excitation energies for the electronic excitations to low-lying excited states have been calculated by the CASPT2 method using cc-pVTZ basis set. The predicted vertical excitation energies are in good agreement with available experimental values. The spin–orbit effect on the spin-forbidden transitions is generally small, with oscillator strengths in the magnitude of 10−7–10−13. The vertical emission energies for the selected excited states were calculated at CASPT2/cc-pVTZ level of theory based on the CASSCF optimized geometries of the corresponding excited states. [Copyright &y& Elsevier]

Abstract: Structures of linear valence isoelectronic carbon chain anions C4O−, C4S− and C4Se− in their ground states have been investigated by density functional theory (DFT-B3LYP) and coupled cluster with single–double substitution (CCSD) approach. Complete-active-space-self-consistent-field (CASSCF) method has been used for geometry optimization of selected low-lying states. The vertical excitation energies from the ground state to selected low-lying excited states have been carried out with complete-active-space-second-order-perturbation-theory (CASPT2). All of them have a similar set of excited states. In comparison with available experimental observations, the predicted excitation energies for the allowed transitions have an accuracy of no more than 0.12eV. Moreover, the calculations here confirm that the previous assignments of the observed electronic absorption bands of C4O− and C4S− are reliable. The excitation energies of 22Π←X2Π and 12Σ−←X2Π transitions in C4Se− are predicted to be 2.09 and 3.90eV, with oscillator strengths 0.1941 and 0.0105, respectively, which may be observed in future experiment. CASPT2 also evaluated the vertical electron detachment energies for C4O−, C4S− and C4Se− to be 3.55, 3.40 and 3.40eV, respectively. [Copyright &y& Elsevier]

Abstract: Extensive theoretical studies on a series of linear phosphaalkynes HC2n+1P and NC2n P have been reported for the first time up to n=10. Density functional theory has been used to explore their equilibrium geometries. It shows a single and triple bond alternation structure for their ground states, in good agreement with the literature values for simple chains. Using time-dependent density functional theory, the vertical excitation energies for the X1Σ+→11Σ+ transition in HC2n+1P and NC2n P have been investigated. The first adiabatic and vertical ionization energies have been obtained by B3LYP method. On the basis of present calculations, the explicit nonlinear expressions for the size dependence of the electronic absorption wavelength (λ) and the first ionization energy (IE) have been suggested, from which we can obtain the values of arbitrary n and the limits for enough large n. Compared HC2n+1P with NC2n P and PC2n P, λ of HC2n+1P is longer than that of NC2n P, but shorter than that of PC2n P; while IE of HC2n+1P is lower than that of NC2n P, but higher than that of PC2n P. According to our study, the former may be caused by the electronic delocalization effect, and the latter may be caused by electronegativity. [Copyright &y& Elsevier]

Abstract: Density functional theory has been used to explore the geometries and vibrational frequencies of the ground states for linear chains PC2n P (n=1–10). The vertical transition energies (E T) for the transition in PC2n P have been studied by time-dependent density functional theory and CASPT2 method. Based on the present calculations, the explicit exponential expression for the size dependence of E T in linear carbon chains has been suggested. The complete active space self-consistent field approach has been employed to locate both the ground state and the selected excited states of PC2n P (n=1–5) for structure comparison. Theoretical investigations on relevant excited states reveal that distinct non-linear spectroscopic feature in such polyynes can be ascribed to difference in bonding between the ground and excited states. At the B3LYP/6-311+G* level, the first adiabatic and vertical ionization energies have been calculated. The dependence relationship between the ionization energies (IE) and the size in linear PC2n P is obtained. E T and IE of PC2n P are compared with those of linear NC2n N and pure carbon chains CC2n C, and they are explained reasonably. [Copyright &y& Elsevier]

Excited-state intramolecular proton transfer (ESIPT) has many important potential applications. In this paper, the geometries of a series of amide-based N H⋯N hydrogen-bonding compounds in their ground S 0 states and first excited singlet S 1 states were optimized with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches. Both topological analysis and noncovalent interactions analysis show strong intramolecular hydrogen-bonds in the studied five systems and the electron density function ρ ( r ) exhibits good linear relationship with the distance of H⋯N 2 . The potential energy curves of the S 0 and S 1 states were scanned by using of DFT and TD-DFT to elucidate the ESIPT process. It reveals that all the systems considered here can undergo an ultrafast ESIPT reaction, with energy barrier of less than 0.05 eV, giving rise to the single fluorescence emission from the proton-transfer tautomer. It is also found that the shorter the hydrogen bond in the normal-form S 1 state, the easier the ESIPT takes place. [ABSTRACT FROM AUTHOR]

The aim of this paper is to design near-infrared (NIR) Al 3+ fluorescent probes based on a Schiff base to extend their applications in biological systems. By combining benzo[ h ]quinoline unit and salicylaldehyde acylhydrazone, we designed two new Schiff base derivatives. According to theoretical simulations on previous experimental Al 3+ probes, we obtained the appropriate theoretical approaches to describe the properties of these fluorescent probes. By employing such approaches on our newly designed molecules, it is found that the new molecules have high selectivity toward Al 3+ and that their corresponding Al 3+ complexes can emit NIR fluorescence. As a result, they are expected to be potential NIR Al 3+ fluorescent probes.

TiO 2 microsphere with tunable pore and chamber size are prepared by a simple solventhermal method and used as catalyst for the photocatalytic CO 2 reduction. It is found that the hollow microsphere with relative lower surface area of 73.8 m 2 g -1 exhibits increased pore size of 18.1 nm and cavity structure, leading to higher CO 2 diffusion coefficient of 5.40 × 10 -5 cm 2 s -1 compared with the solid and yolk/shell microspheres. Therefore, the hollow microsphere possesses more accessible sites for CO 2 adsorption, which finally gives rise to the enhanced CO production rate of 10.9 ± 0.7 μmol g -1 h -1 under simulated sunlight, which is respectively 1.6 and 1.4 times higher than that of solid and yolk/shell microspheres. Electron dynamic study further demonstrates that hollow microsphere shows the highest photocurrent density and the lowest charge recombination among three microspheres structure, which is attributed to the swift CO 2 diffusion providing fresh CO 2 molecules to rapidly scavenge the photo-generated electrons and finally leading to the excellence catalytic reduction performances. This method could be adopted as a general strategy to prepare high performance TiO 2 catalysts with desirable structural qualities for the photocatalytic CO 2 reduction under nature sunlight., (Copyright © 2018 Elsevier Inc. All rights reserved.)

It is well known that interfacial structures and charge transfer in dye-sensitized solar cells are extremely important for the enhancement of cell efficiency. Here, the normal Raman spectra (NRS) and resonance Raman spectra (RRS) of a C343-sensitized TiO2 cluster (Ti9O18) are theoretically predicted from combined electronic structure calculations and a vibrationally-resolved spectral method to reveal the relationship between interfacial geometries and excited-state dynamics. The results show that although the NRS of free C343 and the C343-TiO2 cluster correspond to the vibrational motions of C343 in a high frequency domain, their mode frequencies show obvious differences due to the interaction of the TiO2 cluster on C343, and several new Raman active fingerprint modes, such as bidentate chelating bonding modes, can be used to determine interfacial geometries. However, the resonance Raman activities of low-frequency modes are significantly enhanced and several modes from the TiO2 cluster can be observed, consistent with experimental measurements. Furthermore, the RRS from a locally excited state and a charge transfer state of C343-TiO2 are dramatically different, for instance, new Raman active modes with 1212 cm(-1), 1560 cm(-1) and 1602 cm(-1), corresponding to the motions of CH2 rocking, C=C/C-N/C=O stretching and C=O/C=C stretching, appear from the charge transfer state. The obtained information on mode-specific reorganization energies from these excited states is greatly helpful to understand and control interfacial electron transfer.

Structures and stabilities of linear carbon chains C2n+1S and C2n+1Cl+ (n=0-4) in their ground states have been investigated by the CCSD and B3LYP approaches. The CASSCF calculations have been used to determine geometries of selected excited states of both isoelectronic series. Linear C2n+1S cluster has a cumulenic carbon framework, whereas its isoelectronic C2n+1Cl+ has a dominant character of acetylenic structure in the vicinity of terminal Cl. The vertical excitation energies of low-lying excited states have been calculated by the CASPT2 method. Calculations show that the excitation energies have nonlinear size dependence. The 2(1)Sigma+<--X1Sigma+ transition energy in C2n+1S has a limit of 1.78 eV, as the chain size is long enough. The predicted vertical excitation energies for relatively strong 1(1)Pi<--X1Sigma+ and 2(1)Sigma+<--X1Sigma+ transitions are in reasonable agreement with available experimental values. The spin-orbit effect on the spin-forbidden transition in both series is generally small, and the enhancement of the spin-forbidden transition by spin-orbit coupling exhibits geometrical and electronic structural dependence.