Solid-state spiropyrans exhibiting photochromic properties based on molecular flexibility

Abstract

Solid-state spiropyrans would be excellent materials for solar energy storage, information storage, etc., if they could furnish the light-induced isomerization process at room temperature. However, solid-state spiropyrans with fully reversible photochromic properties at room temperature are extremely rare, due to the lack of sufficient free room for a photoisomerization process. The currently reported solid-state photochromic spiropyrans highly rely on the introduction of bulky rigid groups for creating the needed free room. In this work, via increasing the molecular flexibility, a new strategy for designing solid-state spiropyrans showing highly efficient reversible photochromism at room temperature has been developed. By attaching a flanking alkyl chain to the indole nitrogen, the as-prepared T-type spiropyrans exhibit fast photoresponsive properties. More attractively, this kind of spiropyran could be conveniently “evolved” into a new solid state showing advanced photochromic and thermochromic properties with three different colors. With good room temperature stability and excellent one-to-one correspondences between stimuli and colors, these solid-state spiropyrans are proved to be advanced information storage materials in our logic gate test. This work will provide a new strategy for designing advanced materials with solid-state photochromic molecules in low-molecular-weight.