title: Photochemical synthesis and photophysical properties of coumarins bearing extended polyaromatic rings studied by emission and transient absorption measurements.
abstract: We prepared a variety of coumarin derivatives having expanded π-electron systems along the direction crossing the C3-C4bond of the coumarin skeleton via a photochemical cyclization process and investigated their photophysical features as a function of the number (n) of the added benzene rings based on emission and transient absorption measurements. Upon increasing n, the fluorescence quantum yields of the π-extended coumarins increased. Expanding the π-electron system on the C3-C4bond of the coumarin skeleton was found to be efficient for increasing the fluorescence ability more than that on the C7-C8bond. Introducing the methoxy group at the 7-position was also efficient for enhancing the fluorescence quantum yield and rate of the expanded coumarins. The non-radiative process from the fluorescence state was not substantially influenced by the expanded π-electron system. The competitive process with the fluorescence was found to be intersystem crossing to the triplet state based on the observations of the triplet-triplet absorption. The effects of the expanded π-electron systems on the fluorescence ability were investigated with the aid of TD-DFT calculations.
authors.affiliation: Division of Molecular Science, Graduate School of Science and Engineering, Gunma University, Kiryu, Gunma 376-8515, Japan. yamaji@gunma-u.ac.jp.
authors.forename: Minoru
authors.initials: M
authors.lastname: Yamaji
authors.forename: Yuma
authors.initials: Y
authors.lastname: Hakoda
authors.forename: Hideki
authors.initials: H
authors.lastname: Okamoto
authors.forename: Fumito
authors.initials: F
authors.lastname: Tani
mesh_terms: D003374:Coumarins / Q000737:chemistry*; D003500:Cyclization; D004583:Electrons; D010616:Phenanthrenes / Q000737:chemistry; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry; D013050:Spectrometry, Fluorescence
chemical_list: D003374:Coumarins; D010616:Phenanthrenes; D012997:Solvents; C031181:phenanthrene