Experimental and theoretical study of a new carbazole derivative having terminal benzimidazole rings.

A novel intramolecular donor-acceptor compound has been synthesized and characterized. This compound was a symmetrical A-pi-D-pi-A type molecule containing two benzimidazole rings as two electron acceptors (A) and an N-ethylcarbazole group as electron donors (D). The absorption and emission spectra of the compound were determined by experimental methods in solution and were computed by using the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) in gas phase and in chloroform solution. The calculated absorption and emission wavelengths were in good agreement with the experimental ones. The fluorescence quantum yields and fluorescence lifetimes of the compound in several solvents have been studied by means of steady state and time resolved fluorescence. The results showed the compound had high quantum yield. The cross-section of two-photon absorption (TPA) of the compound was measured by using femtosecond laser in dichloromethane solution. The result indicated the cross-section maximum of two-photon absorption was 430 GM at 600 nm. These results made the compound of great interest as a new fluorescent probe and photoluminescence material.