Controls of photochromic reactions in spiropyran Langmuir-Blodgett films

Abstract

The possibility of controlling photochromic reactions has been investigated in Langmuir-Blodgett (LB) films. The formation of J aggregates of a spiropyran (SP1822) with two long chains has been found previously. We have studied another possibility using LB films of 1′-octadecyl-3′,3′-dimethyl-6-nitro-8-methoxy- spiro[2H-1-benzopyran-2,2′-indoline] (SP1801). SP1801 at the air-water interface gave a monolayer which showed the photomerocyanine form. The LB film of the compound returned to the spiropyran form in the dark. The LB film of the hetero structure with SP1801 and stearic acid, however, turned to J aggregates from the photomerocyanine form spontaneously in the dark. The absorption of the J aggregates was a sharp and intense band, and the half-decay period in the dark was 10 4 times longer than that of conventional spiropyrans. SP1801, in addition to SP1822, is suggested as a candidate for a multifrequency optical memory system with several J-aggregated photochromic compounds having different sharp absorption bands.