TDDFT Investigation and Design for Fluorescent Molecules with Push-Pull Structures

Abstract

The electronic and geometrical structures of the ground and excited states of six fluorescent emitters,namely 3-(dicyanomethylene)-5,5-dimethyl-1-(3-[9-(2-ethyl-hexyl)-carbazol]-vinyl) cyclohexene(DCDHCC),DCDHCC2,3-(dicyanomethylene)-5,5-dimethyl-1(4-diphenylamino-styryl) cyclohexene(DCDPC),DCDPC2,3-(dicyanomethylene)-5,5-dimethyl-1-(4-[9-carbazol]-styryl)cyclohexene(DCDCC),and 3-(dicyanomethylene)-5,5-dimethyl-1-(4-dimethylamino-styryl)cyclohexene(DCDDC) which were specifically designed for organic light-emitting diodes(OLEDs),were studied using density functional theory(DFT) and time-dependent DFT(TDDFT) in conjunction with polarizable continuum models(PCMs).Five hybrid functionals,PBE0,M06,BMK,M062X,and CAM-B3LYP,were used and compared.The experimental spectra of the molecules in acetone solvent were precisely reproduced with the BMK functional.The ionization potential and the electron affinity were calculated to access the properties of the molecules in charge injection.It was found that,when double π-bridges and acceptors were used,the emission of emitters red-shifted to the optimal emitting region.Two brand new molecules,DCDCC2 and DCDDC2,which are the double-branched counterparts of DCDCC and DCDDC,respectively,have been designed.The calculated properties of DCDCC2 and DCDDC2 in spectra and charge injection suggested that they would be as effective in their capacities as fluorescent emitters as the above six emitters.