UV–Vis and ¹H NMR spectroscopic analysis of photodimerization in anthracene-based homopolymers and copolymers

Abstract

Organic conjugated polymers, Polyanthracene (PAn), Anthracene-Pyrrole (An-co-Py) and Anthracene-[1-(2-cyanoethyl)pyrrole] (An-co-CEPy) were synthesized via one-pot chemical oxidation for their photochemical properties, specifically, the photodimerization of their anthracene moieties. Upon irradiation to 397 nm LED light for 90 mins, the UV-Vis absorption peaks of the polymers corresponding to the anthracene groups decreased every 30 mins, suggesting the formation of photodimers, with the rate of photodimerization greatest in An-co-CEPy (0.328). These results were supported by the appearance of new peaks around 6.7 to 6.9 ppm and 4.5 ppm on their ¹H Nuclear Magnetic Resonance spectra after 90 mins irradiation corresponding to hydrogens of the formed anthracene dimers. With each polymer's UV-Vis and ¹H NMR spectra, it was confirmed that all polymers can undergo photodimerization that is distinguishable with other photo-chemical pathways such as photo-oxidation.