Preparation of photochromic spiropyrans linked to methyl cellulose and photoregulation of their properties

Abstract

Spiropyran linked to methyl cellulose (SP–MC) is prepared by the treatment of methyl cellulose with 1′-(2-carboxyethyl)-3′,3′-dimethyl-6-nitrospiro[2H-benzopyran-2,2′-indoline] as a photofunctional material and photoregulation of some of its properties under irradiation with UV light are investigated. The spiropyran moiety in SP–MC is shown to undergo reversible isomerization from the spiropyran form to the merocyanine form under irradiation with UV light of λ= 300–400 nm and from the merocyanine form to the spiropyran form under subsequent irradiation with visible light of λ>550 nm, both in solution and in film, although repeated cycles of the alternate irradiation with UV and visible light resulted in considerable fatigue of the spiropyran moieties over up to 20 cycles. The solubility of SP–MC in benzene and the contact angle of the SP–MC film with water are reversibly regulated under alternate irradiations with UV and visible light. A benzene solution of the SP–MC yielded turbidity under irradiation with UV light and the turbidity disappeared under subsequent irradiation with visible light. The contact angle of the SP–MC film with water decreased under irradiation with UV light and then increased under subsequent irradiation with visible light, the reversible change in contact angle is shown to result from the isomerization of the spiropyran moiety in SP–MC.