Linear and Cyclic Multi-Dithienylethene Molecules: Synthesis, Photochromism, Photothermal Conversion, and Computational Study

Abstract

Photochromic molecules, which undergo changes in both color and chemical structure upon exposure to light, have been extensively studied and widely utilized in photoresponsive applications. In this study, we investigated the interplay between photochromic dithienylethene (DTE) and conjugated double bonds by synthesizing linear and cyclic multi-DTE molecules via McMurry reaction and ring-opening metathesis polymerization. Their molecular structures are characterized by single-crystal X-ray crystallography. These molecules exhibit photochromism with a variety of various colors, including red, yellow, green, light blue, blue, and purple, depending on their substituents and conjugation length. Linear conjugated DTE molecules preferentially undergo cis-trans isomerization due to significant thermal stability of closed-ring DTEs, resulting in thermal ring-opening. In contrast, while the cyclic DTE trimer undergoes photocyclization, the cyclic DTE dimer does not display photochromism. The photoisomerization behaviors of these DTE molecules are further elucidated through DFT calculations. DTE-doped poly(butyl methacrylate) films exhibit enhanced photothermal conversion efficiencies, reaching 28% for the ring-closed form and decreasing to 19% for the ring-open form. These films also demonstrate reversible mechanical deformation under laser irradiation and are applied in capillary actuators, achieving 6% displacement under laser exposure. These findings suggest the potential applications of these materials in light-controlled photochromic inks and microfluidic systems.

Keywords: photochromism, diarylethene, cyclic and linear conjugated molecules, photothermal mechanical conversion, computational calculations