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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]

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 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]

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]

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]

• 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]