Epoxy resin-mediated transformation of chlorophyll-rich photosynthetic pigments extract into high-yield fluorescent products

Abstract

Photosynthetic pigments are predominant natural biomacromolecules crucial for light energy absorption and conversion within photosystems. Here, we report the spectroscopic properties of photosynthetic pigments extracted from spinach leaves incorporated in DGEBA (bisphenol A diglycidyl ether)-based epoxy resin. After resin curing, a visible-light-induced transformation of Chl a, likely associated with the opening of the porphyrin ring, occurred. The structure of the linear Chl a derivative was studied using XPS and ¹H NMR techniques. The phototransformed molecule showed a UV–Vis absorption spectrum lacking the characteristic features of macrocyclic tetrapyrrole pigments, with the absorption maxima being shifted toward shorter wavelengths, compared to the intact Chl a. It is proposed that the photoproduct was derived from the regioselective breakdown of Chl a at the C1−C20 bond position. The results indicate the formation of a luciferin analogue from Chl a, for the first time in an artificial system. Moreover, intensive fluorescence emission at 620 nm, visible even to the naked eye in daylight, was detected. The relative fluorescence quantum yield of the obtained linear tetrapyrrole was estimated at 0.68 and was significantly higher than that measured for Chl a in acetone. These findings not only shed light on the mechanisms underlying pigment transformation but also point toward potential applications in next-generation bioelectronics, including artificial light energy converters, and future bio-inspired energy transfer systems. A comprehensive understanding of these processes may facilitate the development of more effective and efficient artificial photosynthetic systems.