Ab initio studies of the optoelectronic properties of biphenyl derivatives in OLEDs*

The influence of molecular conformation on electron relaxation and photophysical properties of a series of biphenyl derivatives have been investigated using density functional theory (DFT) and time-dependent DFT(TDDFT). The calculated absorption and emission properties of the series as well as phosphorescence quantum yield are in good agreement with the available experimental data. The spin orbit coupling values and the S $\to $ T intersystem-crossing matrix elements and crossing rate constants are also explored as a function of the twist angle between the rings. The T $\to $ S$_{\mathrm{0}}$ radiative and non-radiative transition rates are calculated and discussed for each member of the series. In addition, the T $\to $ S$_{\mathrm{0}}$ radiative transition rate constant is calculated for twisted biphenyls and compared to those for planar molecules.