Theoretical study on the optoelectronic properties of electron-withdrawing substituted diethynylfluorenyl gold(I) complexes

We report on a quantum-chemical study of the electronic and optical properties of gold( I) complex AuTFT ( 1) and its electron-withdrawing substitutents, AuTFOT ( 2) and AuTFCNT ( 3) [ where TFT) diethynylfluorenyl, TFOT = diethynylfluorenone and TFCNT = diethynyl-( 9-( dicyanomethylene) fluorene)]. Our theoretical calculations indicate that for all systems the reorganization energies of electron and hole are in the same order of magnitude and similar to those of the well-known electrontransport material Alq(3). The substitution of -CO and -C( CN)(2) for -CH in AuTFT significantly decreases the bond length alternation and increases the electron affinity, which would effectively lower the energy barrier for electron injection from cathode and thus qualify AuTFOT ( 2) and AuTFCNT ( 3) as candidates for the electron transport layer ( ETL) in light-emitting diodes ( LEDs). The lowest lying excited-states of gold( I) diethynylfluorenyl derivatives have been studied by the singles configuration interaction ( CIS) method and time-dependent density functional method ( TDDFT). It is found that the electron-withdrawing substitutions evidently decrease the energy gap, leading to a remarkable red shift in transition energy and transformation in the direction of charge transfer. Our research is important in the development of new functional materials for the design of LEDs with enhanced performance.