Photoresponsive thiophene-based molecules and materials

Handbook of Thiophene-based Materials Applications in Organic Electronics and Photonics Edited by Igor F. Perepichka and Dmitrii F. Pwepichka 

The C-C distance dependence on photoswitching has been demonstrated using the bis(benzothiophene) series 1-10, all of which are photochromic in solution [27, 28], Derivatives 2-4 and 7-10 (Chart 21.1) all show single-crystal photochromism however, 1,5 and 6 have C-C distances that are too large to allow cyclization (4.35, 4.29 and 4.28 A, respectively) and crystals of them do not change color when irradiated with UV light. 

Reduced photochromic activity is not unique to single crystals and has been observed in other matrices that restrict the molecular movement of the dithienylethene backbone or lock it into the inappropriate conformation. Some particular examples will be mentioned throughout this chapter and, for now, only one 

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