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 o f spironaphthoxazines (SNO) and their merocyanines (EZ, ZZ, EE and ZE) by a b initio methods. We find that in the curves cleavage of the spiro-bond giv es firstly cisoid-ZZ, followed by the two paths to the ZZ isomer by rotatio n of the central C-N single bond or to the ZE isomer by inversion at the ni trogen 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, resp ectively, by rotation of the C=C bond. We also discuss the photochromic pro cess in terms of the behavior of the specific merocyanines involved in the process. (C) 2001 Elsevier Science B.V. All rights reserved.