title: Photochemistry of linear-shaped phenylacetylenyl- and (phenylacetylenyl)phenylacetylenyl-substituted aromatic enediynes.
abstract: The series of linear-shaped phenylacetylenyl- and (phenylacetylenyl)phenylacetylenyl-substituted aromatic enediynes 1-3 were synthesized as pure trans and cis isomers and their photochemistry explored. With expansion of the π-electron system, the absorption spectra red-shifted and the molar extinction coefficients dramatically increased up to 122000 M(-1) cm(-1) for trans-3. The absorption spectra of cis-2 and cis-3 consisted of two independent absorption bands. The fluorescence quantum yields of the molecules were high, even for the cis isomers (Φ(f) = 0.39-0.61). The fluorescence decay of each of the compounds was analyzed as a single exponential and the wavelength dependence of time constants was not observed, indicating a single emitting state in all cases. All isomers exhibited mutual cis-trans photoisomerization. The quantum yield of both trans-to-cis and cis-to-trans photoisomerization considerably decreased in 2 and 3, presumably due to an increased number of photochemical processes that yield nonreactive excited species and which result in nonradiative deactivation. Three energy minima exist in the excited triplet state, where the energy of planar conformation decreased with the extension of the phenyl acetylenyl chain, resulting in the promotion of nonradiative processes without conformational change.
authors.affiliation: Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Sugiyama
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Shinohara
authors.forename: Atsuya
authors.initials: A
authors.lastname: Momotake
authors.forename: Kayori
authors.initials: K
authors.lastname: Takahashi
authors.forename: Yoko
authors.initials: Y
authors.lastname: Kanna
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Nishimura
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Arai
mesh_terms: D053281:Enediynes / Q000138:chemical synthesis*; D005470:Fluorometry; D010777:Photochemistry; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism
chemical_list: D053281:Enediynes