Photochromism of novel chromenes constrained to be part of [2.2]paracyclophane: remarkable ‘phane’ effects on the colored o-quinonoid intermediates??

New Journal of Chemistry Pub Date: 2012-09-18 DOI: 10.1039/C2NJ40575J

Abstract

The photochemistry of rationally designed chromenes that are constrained to be part of [2.2]paracyclophane, i.e., CP-H and CP-OMe, was investigated to examine the effect of through-space delocalization in the cyclophane core (phane effect) on the photochromic behavior. In contrast to the parent chromene, i.e., 2,2-diphenylbenzopyran CH, for which the photoinduced coloration is not observable at room temperature, the cyclophanochromenes CP-H and CP-OMe lend themselves to readily observable photochromism. The photogenerated o-quinonoid intermediates that are responsible for the observed color revert slowly to permit kinetic monitoring of their decays. The difference in the kinetic rate constants for reversion of the photogenerated o-quinonoid intermediates derived from CP-H and CP-OMe attests to remarkable through-space delocalization. To the best of our knowledge, the observed results constitute the first examples of the influence of phane effects on the stabilization or otherwise of the reactive intermediates.

Graphical abstract: Photochromism of novel chromenes constrained to be part of [2.2]paracyclophane: remarkable ‘phane’ effects on the colored o-quinonoid intermediates
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