Tunable circularly polarized luminescence of hybrid supramolecular nanofibers based on a cinnamic acid gelator and spiropyran by photoisomerization

Circularly polarized luminescence materials have attracted plenty of interest by virtue of their fascinating characteristics as well as prospective applications in information encryption, optoelectronic devices, and so on. However, the spatiotemporal modulation of circularly polarized luminescence materials by using light irradiation is still challenging. Herein, we have constructed a kind of hybrid supramolecular nanofibers with tunable circularly polarized luminescence based on photoresponsive chiral cinnamic acid gelator and achiral spiropyran through photoisomerization. The chiral cinnamic acid gelator could self-assemble into nanofiber structures by hydrogen bonding, hydrophobic interaction and π-π stacking, displaying intense right-handed circularly polarized luminescence at 400 nm. However, UV irradiation causes the trans–cis isomerization of the cinnamic acid moiety, resulting in the transformation of nanofibers into rod-like structures and the loss of circularly polarized luminescence signal. In view of this problem, we discovered that the photoisomerized spiropyran can help with the photostability of the nanofibers as well as tuning of their CPL emission, as spiropyran molecule could be transformed into its merocyanine state by ring-opening reaction under 254 nm UV irradiation following with the formation of chiral merocyanine aggregates on the surfaces of the nanofibers. The as-obtained hybrid nanofibers emit both right-handed circularly polarized luminescence at 400 nm and left-handed circularly polarized luminescence at 700 nm with a high luminescence dissymmetry factor. The present study provides a new hybrid strategy to control the photostability as well as regulate the circularly polarized luminescence performance of soft materials.