Theoretical quantum chemical study of spironaphthoxazines and their merocyanines - Thermal ring-opening reaction and geometric isomerization

We calculate potential energy curves of isomerization in the ground state of spironaphthoxazines (SNO) and their merocyanines (EZ, ZZ, EE and ZE) by ab initio methods. We find that in the curves cleavage of the spiro-bond gives firstly cisoid-ZZ, followed by the two paths to the ZZ isomer by rotation of the central C-N single bond or to the ZE isomer by inversion at the nitrogen atom. There is an interconversion path between the resulting ZZ and ZE, through cisoid-ZE. In addition, ZZ and ZE have paths to EZ and EE, respectively, by rotation of the C=C bond. We also discuss the photochromic process in terms of the behavior of the specific merocyanines involved in the process. (C) 2001 Elsevier Science B.V. All rights reserved.