Local and Long-Range Hybrid Density Functional Study on an Organic Light-Emitting Molecule with Pull-Push Structure

Abstract

The absorption and fluorescence spectra of 3-(dicyanomethylene)-5,5-dimethyl-1-(4-[9- carbazol]-styryl)cyclohexene(DCDCC),an organic light emitting material with pull-push structure,were investigated using a time-dependent density functional theory(TD-DFT) approach and bulk solvent effects were taken into account.The performance of eight exchange-correlation functionals including both local and long-range hybrids was assessed by comparing the calculated electron transition energies to experimental observations.It turns out that the appropriate choice of functionals is crucial to obtain an accurate value and BMK hybrids,which contain 44%Hartree Fock exchange,in the frame of DFT and TD-DFT with the polarizable continuum model and a medium sized basis set,emerges as an effective strategy for DCDCC.Moreover,the planar and twisted intramolecular charge transfer(PICT and TICT) models were used to interpret the excited state structure of DCDCC although the charge transfer character of the excited-state was not as intense as to emit obvious double fluorescence.The accurate structures were optimized by BMK and supported the PICT model.