Effects of the acceptor pattern and substitution position on the properties of N-phenyl-carbazolyl based donor–acceptor–donor molecules

Abstract

Four optoelectronic compounds based on the same donor (N-phenylcarbazole) and different acceptors of benzothiadiazole or benzoselenadiazole were designed and synthesized to investigate the effects of the substitution position and effects of the acceptor heteroatom on the properties of N-phenyl-carbazolyl based organic optoelectronic compounds. The results demonstrated that these four compounds have band gaps (2.25 to 2.59 eV) that are lower than that of carbazole (3.20 eV). For the acceptor moiety, the replacement of benzothiadiazole with benzoselenadiazole was beneficial for the polarization of the D–A compound. Different acceptors substituted at the 3-position of N-phenylcarbazole led to molecules with a higher degree of planar conjugation than molecules derived from acceptors substituted at the 2-position. The increase in polarity and conjugation degree of the D–A compounds gave rise to lower band gaps and redshifts in the UV-vis absorption spectra and fluorescence emission spectra compared to the corresponding compounds. Solvatochromism effects were observed for these four compounds in different polar solvents, accompanied by redshifts in the fluorescence emission spectra, which ranged from 509 nm to 596 nm. Using thermogravimetric analysis, the decomposition temperatures of all four materials were found to be above 400 °C.