Optical Control of Aggregation-Induced Emission Shift by Photoisomerizable Precipitant in a Liquid Droplet Microresonator

Emission-switchable fluorophores often include stimuli-responsive units in their molecular structures. This strategy works well, but the applicable compounds are limited to the derivatives of several kinds of photochromic molecules such as diarylethene, azobenzene, and spiropyran. Here, this work presents a simple methodology based on a photoresponsive precipitant for achieving color-switchable photoluminescence. A luminescent dye, cyano-substituted oligo(phenylenevinylene) (COPV), features both twisted intramolecular charge transfer and aggregation-induced emission shift properties, leading to the change in the luminescence color from green to red upon precipitation. The COPV, together with photoisomerizable precipitant azobenzene (C6), is doped into spherical droplets of epoxy resin (ER) in a liquid state. The photoisomerization of C6 induced by UV irradiation and heating alternatively precipitates out and dissolves COPV in ER and changes the photoluminescence color, while maintaining the optical microresonator properties. This study will open a promising way for assembling/disassembling novel emission color-switchable systems.