First Principles Study of Dendritic Carbazole Photosensitizer Dyes Modified with Different Conjugation Structures

Abstract

In the pursuit of efficient organic dyes first principles calculations were carried out by using density functional theory (DFT). The electronic and optical properties of D−D-π-A carbazole dendritic donor and cyanoacrylic acid acceptor conjugated through thiophene and oxadiazole structures are being reported. The findings of this work point to the dependence of the structural modifications especially changes in length of conjugation molecule appeared to notably affect the properties of the dyes. The positions of highest occupied molecular orbital (HOMO) and lowest molecular orbitals (LUMO) energy levels are found suitable for electron reduction and electron injection processes respectively. The addition of another oxadiazole ring as well as replacement of a thiophene ring with existing oxadiazole in the conjugating bridge appeared to reduce the HOMO-LUMO energy gap. TD-DFT excitation spectra calculated at PBE, B3LYP and CAM−B3LYP levels of theory are discussed in detail to shed light on charge transfer process in the dye molecules and the calculated results are found consistent with reported experimental work. The changes in length and structure of π-spacer chain are discussed to analyze the photon to current conversion efficiency.