Thermal and photoreductive elimination from the tellurium center of π-conjugated tellurophenes.

This study introduces small molecule tellurophenes that can undergo photoreductive elimination. A tellurophene compound with strong light absorption properties and extended π-conjugation, 2,5-bis[5-(N,N'-dihexylisoindigo)]tellurophene (1), has been synthesized. Halogen oxidative addition to the tellurium center from various halogen sources gives the dibromo- (1Br2) and dichloro- (1Cl2) adducts, leading to a red-shift in the optical absorption properties. In the presence of excess opposing halogen, 1Br2 and 1Cl2 can interconvert, with equilibrium favoring the dichlorotellurophene adduct. Reductive elimination reactions were studied using optical absorption spectroscopy, NMR spectroscopy, thermogravimetric analysis, and matrix-assisted laser desorption/ionization (MALDI) analysis. Thermal reductive elimination from 1Br2 and 1Cl2 occurs in the solid-state to restore 1. Photoreductive elimination occurs under irradiation with green (505 nm) light in solution in the presence of a halogen trap with some decomposition. This is the first example of photoreductive elimination from a mononuclear tellurophene complex.