Theoretical study on photophysical properties of 2,1,3-benzothiadiazole-based star-shaped molecules.

Liu, Ying-Fang; Ren, Xue-Feng; Zou, Lu-Yi; Ren, Ai-Min; Feng, Ji-Kang; Sun, Chia-Chung

Star-shaped molecules with tailoring functional groups in the core and the arms have great potential application in organic light-emitting devices, because it can be designed to realize low band gap, broad absorption, and excellent solubility for low-cost solution process. To gain an insight into the structure-property relationships, a set of four-arm star-shaped molecules with 2,1,3-benzothiadiazole as the core, different π-conjugated groups as the arm, and triphenylamine or 2-(pyridin-2-yl) pyridine as the end-group were designed. In this study, a systematic investigation into them was carried out using the density functional theory and time-dependent density functional theory methods. The calculated ionization potentials, electron affinities, and reorganization energies (λ) show that the properties of the π-conjugated bridge and the end-group significantly affect the carrier injection and transport characteristics of these molecules, especially for S-BTDP and S-EBTD. Among these molecules, S-BTDP exhibits better electron injection ability due to the introduction of 2-(pyridin-2-yl) pyridine as the end-group. However, S-EBTD, with ethylene as π-conjugated bridge, has excellent hole injection and carrier transport behaviors. We also calculated the singlet-to-triplet exciton-formation cross-section ratio (σ/σ), the exciton-formation fractions (χ), and the absorption and emission spectra of these molecules. We calculated that σ/σ ranges from 1.78 to 2.76 and that χ is ca. 0.37-0.48. These molecules have two absorption bands in the range of 340-410 nm and 500-613 nm, respectively. The calculated emission spectra range from 619 to 706 nm. It can be deduced that the studied 2,1,3-benzothiadiazole-based star-shaped molecules can serve as efficient red light-emitting electroluminescent materials.

THIADIAZOLES; MOLECULAR structure; FUNCTIONAL groups; LIGHT emitting diodes; ENERGY bands; ABSORPTION; DENSITY functionals; CHARGE transfer

Theoretical Chemistry Accounts: Theory, Computation, & Modeling, 2011, Vol 129, Issue 6, p833

1432-881X

Academic Journal

10.1007/s00214-011-0942-8