Highly efficient synthesis and photochromic properties of a pentacyclic N-heterocyclic carbonyl-based dithienylethene

Given that the photochromic functional materials possess outstanding phototropic color-change properties, the attention being paid to this field is progressively intensifying. The development of N-heterocyclic carbonyl photoswitching materials, harnessing dithienylethene site for photochromism, typically involves a complex multi-step synthesis process, which substrate diversification and the complexity of the preparation process are confronted with various challenges. Herein, we present a straightforward synthetic methodology for the preparation of photochromic 4,5-bis(2,5-dimethylthiophen-3-yl)-1,3-diphenyl-1,3-dihydro-2H-imidazol-2-one (1o) via reprogramming the synthesis pathway of dithienylethene-containing imidazolone using 1,3-diphenylurea. The current method demonstrates efficient reaction between α-hydroxy ketone and 1,3-diphenylurea in high yield, thereby enabling direct and straightforward one-step cyclization. The grown crystal sample of the targeted 1o has undergone single crystal X-ray diffraction analysis to elucidate its structural information. The ring-open (o-isomer) and ring-closed (c-isomer) forms showing remarkable fatigue resistance and high contrast visual color changes, can be effortlessly interconverted through the alternating irradiation of UV/vis light. To illustrate the electronic structure of the isomers, thorough analyses of the frontier molecular orbital based on TD-DFT calculations were conducted.