Photophysics and kinetics of naphthopyran derivatives, Part 2: Analysis of diarylnaphthopyran kinetics. Degeneracy of the kinetic solution

The photocoloring and fading kinetics of the photochromic 3,3-diphenyl-3H-naphthol vertical bar 2, 1 -b vertical bar pyran (NPY) have been analyzed using a kinetic treatment for three related species recently developed by us (Int J Chem Kinet 2005, 37(3), 162). The concepts of identifiability and distinguishability are developed with respect to the elucidation of the NPY kinetics. We find that neither set of kinetic data on its own, nor the two data sets combined, allow the true mechanism to be distinguished. In addition, even for a chosen mechanism, there exist degenerate sets of parameters i.e. the solutions are also unidentifiable. A discussion of the limits and uniqueness of the results' interpretation is presented. (c) 2005 Wiley Periodicals, Inc.