Spiropyran–cholesterol conjugate as a photoresponsive organogelator

Abstract

We synthesized a spiropyran–cholesterol conjugate (1) and studied its gelation and photochromic properties. The compound 1, when dissolved in carbon disulfide (CS₂), forms a homogeneous gel at −40 °C due to the van der Waals interaction between the cholesterol moieties. UV or visible light irradiation of the CS₂ sol or gel promotes a reversible change in color between yellow and purple without phase transition. This is promoted by reversible photoisomerization of the spiropyran moiety between the spirocyclic (SP) and the spirocycle-opened merocyanine (MC) form. In contrast, 1 forms a gel in benzyl alcohol (BA) at room temperature. The BA gel also exhibits a reversible color change upon UV/visible light irradiation, but the BA sol always shows a purple color due to the stabilization of the MC form by strong H-bonding interaction with solvents. The BA gel is successfully applied as a material for information storage, easily writable and erasable by light irradiation.