Spectral response of pyridine-terminated thieno[3,4-c]pyrrole-4,6-dione derivatives to boron-containing Lewis acids

Abstract

Optical band gap is an important parameter of organic semiconductors, which determines their performance and applications. In this paper, two thieno[3,4-c]pyrrole-4,6-dione (TPD) derivatives TPD-2-Py and TPD-4-Py terminated by 2- and 4-substituted pyridine are designed and synthesized with Stille reactions. The results of nuclear magnetic resonance spectra, absorption spectra and emission spectra confirm that TPD-2-Py and TPD-4-Py cooridinate with a Lewis acid tris(pentafluorophenyl)borane (BCF) through the nitrogen atom on the pyridine ring instead of TPD unit. The absorption spectra show that TPD-2-Py and TPD-4-Py have similar absorption, but their absorption spectra are red-shifted after cooridinating with BCF. Further titration experiments indicate that TPD-4-Py is more easily coordinated with BCF, and the maximum absorption peak of TPD-4-Py and BCF complex is bathochromic shift comparing with that of TPD-2-Py and BCF complex. These results demonstrate that the substituted position of pyridine has an important influence on the coordination ability of BCF, and further regulation of the optical band gap can be achieved by changing the substituted position of pyridine substitutents.