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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]

A step-by-step theoretical protocol based on the density functional theory (DFT) and time-dependent DFT (TD-DFT) has been performed to study a Ruthenium polypyridyl complex named cis-dithiocyanatobis-(4,4′-dicarboxy-2,2′-bipyridine) ruthenium(II) (N3) sensitized TiO 2 solar cell including dye excitations and electronic injection. Three binding structures of N3 anchored to a TiO 2 nanoparticle (TiO 2 ) 38 have been adopted. The electronic structures and optical properties of N3 dye in gas phase, in solutions (with the explicit and implicit solvent models), and interfaced with TiO 2 have been calculated. The hybrid DFT exchange-correlation (XC) functional B3LYP and PBE0, the newly-modified PBE0 functional PBE0-1/3, and the long-range corrected DFT (LRC-DFT) XC functional Cam-B3LYP have been applied. It is found that both the DFT XC functionals and molecular environments play a crucial role on molecular properties, which affect both the spectral lineshapes and peak positions. Coupled with PCM model, TD-PBE0-1/3 produces the best result compared with the experimental spectrum of N3 in CH 2 Cl 2 , TD-B3LYP slightly underestimates the excitation energies, and TD-Cam-B3LYP overestimates the excitation energies of 0.4–0.5 eV. As the solvent polarity increases, the electronic absorption spectra of N3 dye blue shift. The absorption manners of N3 anchored to (TiO 2 ) 38 affect the electronic excitations, leading to different electronic injection pathways. Two of three anchoring manners favor the interfacial electronic transfer. In the end, three possible electronic injection pathways from the different parts of the excited dye to TiO 2 nanoparticle have been suggested, indicating the different timescales of electron injections. [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]

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]

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]