DFT/TDDFT, NPA, and AIM-based study of the molecular switching properties of photocyclization and metallochromism of the DAE complexes

Abstract

Diarylethene (DAE), the ubiquitous photochromic unit, is one of the most promising candidates for well-recognized optoelectronic applications. In this paper, the relationship between reversible photoisomerization/metallochromic properties and second-order nonlinear optical (NLO) responses for a new photochromism based on DAE with a benzyl-linked 8-aminoquinoline-2-aminomethylpyridine unit (1O) has been systematically investigated by using density functional theory. Our results show that closed-ring (1C) comprising DAE unit was shown to be capable of exhibiting both large static first hyperpolarizabilities βtot (1.075 × 10−28 esu) and large switch ratio βratio ~ 31 with corresponding open-ring because of the better delocalization of the π-electron system, the more obvious degree of charge transfer and the smaller transition energy in the closed-ring. When the metal ions have been injected in open-ring (1O*M), we observed a larger NLO response compared with the corresponding open-ring 1O. However, it can slightly decrease the βtot values in 1C*M. Natural bonding orbital and atom in molecules analysis provide a better understanding for the property differences in metallochromic process. We hope this research would be beneficial for further theoretical and experimental studies on large second-order NLO switches applications.