Ring transformations of heterocyclic compounds. XXIII. The UV irradiation product of photochromic 2,4,6‐triaryl‐1‐(spiro[2H‐l‐benzopyran‐2,2′‐indoline]‐6‐yl)pyridinium salts ‐ A phenolate betaine or a pyridinium substituted merocyanine dye?

Abstract

AbstractThe synthesis of the novel 2,4,6‐triaryl‐1‐(spiro[2H‐1‐benzopyran‐2,2′‐indoline]‐6‐yl)pyridiniumper‐chlorates 4 by reaction of 5‐nitrosalicylaldehydes 6 with 1,3,3‐trimethyl‐2‐methyleneindoline (7) to 6‐nitro‐spiro[2H‐1‐benzopyran‐2,2′‐indolines] 1, their stannous chloride reduction to the 6‐amino derivatives 8, followed by a 2,6‐[C5+N] ring transformation with 2,4,6‐triarylpyrylium perchlorates 9, is reported. UV irradiation experiments in twenty solvents of different polarity prove their photochromic properties and show that the photochemically generated negative solvatochromic dyes 5, formed by ring opening of the benzopyran moiety of 4, are rather merocyanine than pyridinium phenolate betaine dyes.