Nobuaki Nakashima

Enhancement of luminescence of Nd3+ complexes with deuterated hexafluoroacetylacetonato ligands in organic solvent

Abstract Tris-(hexafluoroacetylacetonato)neodymium(III), [Nd(HFA-D)3], was prepared by chelation of Nd3+ ion with deuterated hexafluoroacetylacetone in CD3OD. Luminescence of the Nd3+ complex was observed for the first time in organic solvents and the quantum yield was estimated to be of the order of 10−2 in deuterated acetone solution. The absorption spectrum of [Nd(HFA-D)3] dissolved in acetone was comparable with that of Nd3+ ion in Y3Al5O15 matrix (Nd:YAG). Splitting of the 4 F 3 2 level was determined to be 82.3 cm−1 in this system. These spectral characteristics suggest that the physical nature of Nd3+ coordination environments should be uniform and well defined by coordination of HFA in solution.

Characteristic emission of β-diketonato Nd3+ complexes dressed with perfluoroalkyl groups in DMSO-d6

Abstract Tris(bis(perfluorooctanoyl)methanato)neodymium(III), Nd(POM-D) 3 , was successfully synthesized to induced efficient emission in DMSO- d 6 . While the emission quantum yield of the tris(hexafluoroacetylacetonato)neodymium(III), Nd(HFA-D) 3 , system decreased as the concentration increased, the Nd(POM-D) 3 system gave almost constant quantum yield (3.2%) in DMSO- d 6 ranging in concentration from 0.01 to 0.07 M. The enhanced and characteristic emission of the Nd(POM-D) 3 system suggests that dipole-dipole energy transfer via cross-relaxation through collisions between Nd 3+ complex molecules should be suppressed in the fluid system by use of the bulky diketonato complex of Nd 3+ .

Quantum yields of hydrated electrons by UV laser irradiation

Abstract Quantum yields of hydrated electrons of Cl−, Br−, I−, SO2−4, SCN− and OH− in aqueous solution have been determined by means of 193 nm laser flash photolysis. Shorter wavelength excitation showed higher quantum yields for I− and SCN− ions in three wavelengths of 193, 222 and 248 nm. The highest yield was 0.73 for SO2−4 at 193 nm and the lowest one was 0.015 for SCN− at 248 nm.

Picosecond flash photolysis and transient spectral measurements over the entire visible, near ultraviolet and near infrared regions

Abstract We have developed a picosecond flash photolysis method together with transient spectral measurements over the entire visible, and some parts of the near UV and near IR regions. S n ← S 1 absorption spectra of anthracene were obtained as microdensitometer tracings of photographs throughout the region 390–920 nm. Some other results of picosecond studies on the primary processes in exciplexes are also reported briefly.

Higher yield of photoreduction from Eu3+ to Eu2+ with shorter wavelength irradiation

Abstract We have found that the photoreduction yield from Eu3+ to Eu2+ depends on excitation wavelength within a single charge-transfer band. The quantum yields φ were 0.12 ± 0.02 (at 193 nm) and 0.06 ±0.01 (at 222 nm) in aqueous solution, and 0.42 ± 0.07 (at 222 nm) and 0.35 ± 0.06 (at 248 nm) in methanol solution. The escape probability of Eu2+ from the photochemically prepared geminate pair is suggested to be higher with shorter-wavelength excitation.

Intersystem crossing in anthracene-N,N-diethylaniline exciplex

Abstract The growing-in of the anthracene triplet state has been measured in the case of the anthracene-N,N-diethylaniline exciplex system in hexane. The anthracene triplet state is formed from the relaxed exciplex fluorescent state.

High photoreduction yield of Eu3+ to Eu2+ in alcoholic solutions and its wavelength dependence

Abstract Photoreduction yields of Eu3+ to Eu2+ in aqueous and alcoholic solutions were determined. The highest quantum yields were found to be 0.97 ± 0.16 for EuCl3 in methanol under 308 nm excitation and 0.94 ± 0.17 in 2-propanol under 248 nm excitation. The lowest quantum yield was 0.12 ± 0.02 for Eu(ClO4)3 in aqueous solution under 193 nm excitation. The high photoreduction yields for EuCl3 indicate that Cl reacts efficiently with neighbouring alcohols. The yield was found to depend on the excitation wavelength for EuCl3 in methanol solution.

Time-resolved fluorescence spectra of s-tetracyanobenzene-toluene complex

Abstract Time-resolved CT (charge transfer) fluorescence spectra and the fluorescence rise and decay curves at various wavelengths of the CT fluorescence band have been measured for the s -tetracyanobenzene (TCNB)-toluene system at various temperatures. The measurements have demonstrated clearly the relaxation process including the surrounding solvent molecules from the Franck-Condon state to the equilibrium state of the complex, resulting in the extraordinary large Stokes shift of the CT fluorescnece.

Measurements of absorption spectra of pyreneN,N-diethylaniline exciplex in various solvents with picosecond laser photolysis method

Abstract The absorption spectra of the pyreneue5f8N,N-diethylaniline exciplex are rather similar to the superposition of the absorption bands of pyrene anion and diethylaniline cation. The lower the polarity of the solvent, the broader are the observed spectra. Explanations for this result are given.

Two-photon reduction of Eu3+ to Eu2+ via the f′ ← f transitions in methanol

Abstract Two-photon absorption has been found to induce the photoreduction of Eu 3+ to Eu 2+ in methanol solution of EuCl 3 . The excitation spectra clearly indicate that the photoreduction occurs via a 4f′ ←4f transition. The second photon is presumed to be absorbed in a transition band of an intermediate level to a charge-transfer level. The reduction efficiency was about 3 × 10 −5 for the excitation at 464.7 nm under 460 mJ/cm 2 .