Spiropyrans with Long-wavelength Absorption

the condensation of 2-phenyl-l,3,6-trimethyl-2-azaazulenium perchlorate with 5-nitrosalicylaldehyde gave the cationic styryl dye (A,max 510 nm) in 56% yield.139 This dye is the salt of the open form of the corresponding spiropyran, and upon treatment with base, a reaction which was not originally reported, was found to give the expected dye (126), which absorbs at 733 and 536 nm. This material did not thermally fade or photobleach to any significant extent with visible light in either polar or nonpolar solvents.7 

A recent review discusses the synthesis, spectral properties, and photochemical behavior of novel spirobenzopyrans, Spiro-1,4-oxazines, and 2//-chromenes. It emphasizes the structural features needed for infrared-absorbing photoisomers, luminescent stable forms, improved fatigue resistance, and spiropyrans exhibiting photochromism in vacuum-deposited films.147 

---