Abstract: Three indolinospironaphthopyrans: 1',3'-dihydro 1',3',3'-trimethyl spiro [2H-indole-2,3-(3H)naphtho [2,1-b] pyran], 1',3'-dihydro-3',3'-dimethyl-1-(2-hydroxyethyl)-spiro [2H-indole-2,3-(3H)naphtho [2,1-b] pyran], 1',3'-dihydro-3',3'-dimethyl-1-(5-iodo-3-oxypentyl)-spiro [2H-indole-2,3-(3H)naphtho [2,1-b]pyran were synthesized, and their photochromic reactions were studied using nanosecond laser photolysis technique. Photolysis of these compounds in acetonitrile and in tetrahydrofuran leads to the formation of the long-lived photomerocyanine(PMC) as the predominant photoproduct.The formation of the PMC occurs owing to C-O bond opening, mainly directly from the excited single state of the spiropyran(SP). From the absorption bands, it has been speculated that the substituents of the nitrogen atom of the indole ring influence the structural characteristics of the PMC mainly through steric hindrance effects. A potential energy surface model is established to explain the results.

Key words: Spironaphthopyran, Photochromism, Laser photolysis, Time-resolved spectra