Toshifumi Morita

Fluorescence quenching of aromatic molecules by inorganic anions

Abstract Fluorescence quenching of aromatic molecules by inorganic anions in H 2 OEtOH mixtures at 300 K has been studied quantitatively. A linear relationship between log k q ( k q is the quenching rate constant) and Δ G (the free energy change in electron transfer) is obtained indicating that the anion-induced quenching proceeds via an electron-transfer pathway. The potential barrier Δ G ‡ in the electron-transfer process is also given as a function of Δ G according to the Horiuchi-Polanyi rule.

Influence of triplet—triplet excitation transfer on the decay function of donor luminescence

Abstract The triplet—triplet electronic excitation transfer from benzophenone to naphthalene in rigid solutions has been investigated by measuring the non-exponential decay curve of benzophenone photphorescence using a laser pulse for excitation. The results of measurements were satisfactorily reproduced by Inokuti—Hirayamas formula based on Dexters theory of exchange interaction.

Weak fluorescence from the S2(1Lb) state of biphenylene

Abstract Weak fluorescence from biphenylene has been observed in some solvents [λmax:480 nm, φf = 1.0 (±0.3) × 10−4 at 350 nm and 20°C]. The fluorescence is assigned to S2(1Lb)→So(1A) by means of the fluorescence polarization method. The S2 fluorescence in cyclohexane was wavelength-dependent. Repid radiationless processes in excited biphenylene are also discussed.

Proton-induced radiationless processes in excited 9,9′-bianthryl

Abstract Dynamic quenching of excited 9,9′-bianthryl (BA) induced by proton has been studied by means of nanosecond time resolved spectroscopy. An efficient fluorescence quenching by sulfuric acid was observed in polar solvents (e.g., 1Kq = 1.54 × 109 M−1 s−1 in MeOH at 298 K). The quenching involves intersystem crossing (k′isc ≈ 54 × 108 M−1 s−1) and another radiationless process, probably internal conversion, (k′n ≈ 1 × 109 M−1 s−1). The quenching rate constant in the triplet state 3kq was about a factor of 103 less than 1kq. Isotope effect on the quenching was also examined.

Hydrogen atom abstraction by p-chloranil triplet from tetrachlorohydroquinone and the presence of a competitive deactivation process

Efficiencies of the formation of p-chloranil semiquinone radicals from p-chloranil triplet were determined in the p-chloranil—tetrachlorohydroquinone systems by laser flash spectroscopy. The hydrogen abstraction occurs depending on solvent polarity and competes with another deactivation process. This result suggests the existence of the triplet exciplex as an intermediate.

Formation of contact ion-pair and dissociated ion-radicals by electron transfer from excited amine to oxygen molecules

Abstract It has been confirmed that ion radicals formed by electron transfer from the excited DPPD (N,N-diphenyl-p-phenylenediamine) to oxygen molecules form contact ion-pairs in nonpolar solvents, while they dissociate owing to the strong solvation in polar solvents.

KINETIK UND MECHANISMUS DER PHOTOLYSE VON 2,2′‐MERCAPTO‐BENZOTHIAZOLYLDISULFID IN LOESUNG

Die Photolyse der Titelverbindung in Athanol bei 2 537 A und 20°C fuhrt zu 2-Mercapto-benzothiazol, dessen Quantenausbeute von der Konzentration der Ausgangsverbindung und der Bestrahlungszeit unabhangig ist, jedoch stark mit steigender Lichtintensitat abnimmt.