Enhanced Photochemical Sensitivity in Photochromic Diarylethenes Based on a Benzothiophene/Thiophene Nonsymmetrical Structure

• Published in: European journal of organic chemistry Vol. 2014; no. 32; pp. 7165 - 7173
• Main Authors: Galangau, Olivier, Kimura, Yuka, Kanazawa, Rui, Nakashima, Takuya, Kawai, Tsuyoshi
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.11.2014; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Subjects: Chemistry; Chemistry, Organic; Density functional calculations; Diarylethenes; Noncovalent interactions; Photochromism; Physical Sciences; Science & Technology; Photochromism; SINGLE-CRYSTALLINE PHOTOCHROMISM; QUANTUM YIELDS; DITHIENYLETHENE; OPTICAL-PROPERTIES; Diarylethenes; Density functional calculations; PHOTOCYCLIZATION; DERIVATIVES; Noncovalent interactions; MOLECULES; FAMILY
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201402774

Photosensitivity of molecules is one of the central subjects of organic photochemistry. In this article, we present how and why a benzothiophene moiety impacts the photochromic quantum yield for the photochemical pericyclic ring closing of the hexatriene moiety. Two compounds were prepared: a symmetrical one incorporating two fluorenylthiophene units, and its corresponding nonsymmetrical partner, where one of the thiophene units was replaced by a benzothiophene group. Interestingly, the latter presents relatively high cyclization quantum yield (0.74), a value close to the largest one so far reported. Based on crystal structures, VT‐NMR data and DFT calculations, we demonstrate that introducing a benzothiophene in the molecular scaffold induces skeleton stiffening by means of CH–π interactions and steric repulsions, and leads to increased population of the reactive conformer in the ambient conditions. We provide evidence (VTNMR, X‐ray data, DFT simulations) that a standard nonsymmetric diarylethene containing a benzothiophene unit achieves high ring cyclization quantum yield by means of favorable intramolecular interactions (CH–π, H–F bonding or steric hindrance).