title: Photochemical E (trans)-->Z (cis) isomerization in substituted 1-naphthylacrylates.
abstract: Substituted naphthylacrylates, 1-3, not showing rotamerism have been synthesized with a view to study photochemical E (trans)-->Z (cis) isomerization. Photostationary state composition of the isomers upon direct excitation, triplet sensitized isomerization, quantum yield of isomerization, and steady state and time-resolved fluorescence behavior have been studied for these naphthylacrylates. The direct excitations of the compounds yield high Z (approximately 80%) isomer composition, whereas the triplet sensitization results in less Z (approximately 20%) isomer composition. This indicates that the singlet pathway is very efficient in converting the E isomer to the Z isomer. The naphthylacrylates 1 and 2 exhibit structured fluorescence at room temperature in hexane and upon changing the solvent to CH3CN; the structure of the fluorescence is lost, indicating that the singlet excited-state develops a polar character in a polar environment. The polar nature of the singlet excited state becomes more clear in the case of 3 from its fluorescence solvatochromism. The naphthylacrylates did not exhibit excitation wavelength-dependent fluorescence at room temperature suggesting that the ground state conformers (rotamers) are not involved. Fluorescence lifetimes measured for these compounds displayed biexponential behavior, which is explained using a two-state model.
authors: Organic Chemistry Division II, Indian Institute of Chemical Technology, Hyderabad-500 007, India.
authors: K M
authors: KM
authors: Bushan
authors: G V
authors: GV
authors: Rao
authors: T
authors: T
authors: Soujanya
authors: V J
authors: VJ
authors: Rao
authors: S
authors: S
authors: Saha
authors: A
authors: A
authors: Samanta