Multimode-Photochromism Based on Strongly Coupled Dihydroazulene and Diarylethene

✍ Scribed by Thomas Mrozek; Helmut Görner; Jörg Daub

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 254 KB
• Volume: 7
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/1521-3765(20010302)7:5<1028::aid-chem1028>3.0.co;2-7

✦ Synopsis

Synthesis and photophysical/ photochemical investigations of 1,8adihydro-2,3-bis(2,5-dimethy-3-thienyl)azulene-1,1-dicarbonitrile (1 A) and 1,8a-dihydro-2,3-diphenylazulene-1,1-dicarbonitrile (2 A) are reported. The photoprocesses and thermal reactions of systems 1 and 2 were studied by timeresolved and steady-state techniques under various conditions. The dihydroazulene (DHA) ± dithienylethene (DTE) conjugate 1 A is photochemically con-verted into the dihydrothienobenzothiophene (DHB) isomer 1 C and the vinylheptafulvene (VHF) isomer 1 B. System 2 exhibits exclusively DHA/VHF photochromism. For both systems the VHF form thermally reverts back into the DHA form. Their rate constant (k B3A ) increases with the solvent polarity and the relaxation kinetics proceed by means of an activation barrier of 65 ± 80 kJ mol À1 ; k B3A and the activation parameters of the isomerisation reactions are rather similar. The photostationary state of the 1 A 3 1 B and 1 A 3 1 C photoisomerisation is sensitive to the irradiation wavelength. The concept of cycloswitching is discussed.