Journal
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY
Volume 2015, Issue 7, Pages 1403-1408Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/ejoc.201403403
Keywords
Photochromism; Cyclophanes; Chromenes; Phane effect; Conjugation
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Funding
- Rajiv Gandhi University of Knowledge and Technology-IIIT-Nuzvid
- Council of Scientific and Industrial Research (CSIR), New Delhi
- CSIR
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The photochromism of a chromene annulated on [2.2]paracyclophane, Ac-CPC, was investigated. Whereas the parent chromene 2,2-diphenylbenzopyran shows photoinduced coloration only at very low temperatures, acetyl-cyclophanochromene Ac-CPC was found to exhibit room-temperature photochromism. With no extended conjugation due to absence of any substituents in two cofacially-oriented aryl rings, the through-space delocalization of p-electrons, i.e., the phane effect, manifests nicely leading to the stabilization of the photogenerated colored o-quinonoid intermediates. The interaction between cofacial aryl rings is supported by the distance between them, as revealed by X-ray crystal structure analysis. Additionally, electrophile ... nucleophile interactions are surmised to be important for intriguingly longer persistence of the photogenerated intermediates of Ac-CPC relative to the lifetime of the photogenerated intermediate generated from the parent cyclophanochromene, which is devoid of an electron-withdrawing acetyl group.
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