Chunsheng Qin

Theoretical Characterization of a Typical Hole/Exciton-Blocking Material Bathocuproine and Its Analogues

The structural, electronic, and carrier transport properties of bathocuproine (BCP), which is a typical hole/exciton-blocking material applied in organic light-emitting diodes (OLEDs), have been investigated based on density functional theory (DFT) and ab initio HF method. The detail characterizations of frontier electronic structure and lowest-energy optical transitions have been studied by means of time-dependent density functional theory (TD-DFT). Five BCP analogues, o-phenanthroline (1), 2,9-dimethyl-1,10-phenanthroline (2), 2,9-diphenyl-1,10-phenanthroline (3), 4,7-diphenyl-1,10-phenanthroline (4), and 2,9-bis(trifluoromethyl)-1,10-phenanthroline (5) have also been studied in order to select more suitable candidates of efficient hole-blocking materials. The calculated results showed that rigid planar structures, conjugate degrees, and substitute groups play crucial roles in the hole/exciton-blocking and electron-transport properties of these materials. The calculated geometries, ionization energies (IP), and energy gap between the singlet ground state and triplet excited state (E(T1)) were well in agreement with the experimental results. On the basis of the incoherent transport model, the calculated electron mobility of BCP is 1.79 x 10(-2) cm(2)/(V s), which is comparable to experimental results of 1.1 x 10(-3) cm(2)/(V s). The electron mobilities for compounds 1, 4, and 5 are 3.45 x 10(-2), 2.90 x 10(-2), and 1.40 x 10(-2) cm(2)/(V s), respectively. The calculated results indicated that compounds 1, 4, and 5 may be more effective hole/exciton-blocking materials than BCP.

Predication of second-order optical nonlinearity of [(Bu2tIm)AuX] (X=halogen) using time-dependent density-functional theory combined with sum-over-states method

The dipole polarizability and second-order polarizability of recently synthesized (1,3-di-ter-butylimidazol-2-ylidine) gold complexes [(Bu2t Im)AuX] (X=halogen) were investigated by using time-dependent density-functional theory combined with sum-over-states method. We have discovered that these complexes possess remarkably larger molecular second-order polarizability compared with the organometallic and organic complexes. The value of the second-order polarizability increases in the order of F<Cl<Br<I. The analysis of the molecular orbital suggests that the charge transfer from halogen atom to the carbene ligand plays the key role in nonlinear optical response of gold complexes. The gold of these complexes is a bridge of charge transfer, unlike other organometallic complexes, the metal center may be a strong donor or acceptor. These complexes have a possibility to be excellent second-order nonlinear optical materials from the standpoint of transparency, relatively large beta values and relatively small dispersion behaviors.

Calculated UV-Visible spectra and third-order nonlinear optical properties of heteroaromatic derivatives of stilbene inserted with 1,3-squaraine

Based on the geometry optimized by semi-empirical PM3 method, UV-visible spectra and second-order hyperpolarizability γ of the heteroaromatic derivatives of stilbene inserted with 1,3-squaraine were calculated by ZINDO/CI-SOS method. The relation between y and molecular structures was discussed. It is shown that the heteroaromatic derivatives of stilbene inserted with 1.3-squaraine will be promising candidates for nonlinear optical materials. which have both larger γ values and high transparency.