Tohru Azumi

Measurement of the triplet lifetime and the quantum yield of triplet formation of phthalazine by the time-resolved thermal lens method

Abstract The time-resolved thermal lens technique is used to determine the quantum yield of the triplet formation and the triplet lifetime of phthalazine in a polar and a non-polar solvent. The quantum yields of phthalazine in ethanol and benzene are 0.44 and 0.49, respectively. Very short triplet lifetimes of phthalazine (2.7 μ;s) in benzene at room temperature are reported.

The quantum yield of triplet formation and triplet lifetime in the solid phase by a time-resolved thermal lens method. Application to pyridazine

Abstract The time-resolved thermal lens technique is used to measure quantum yields of triplet formation and triplet lifetime in the solid phase at low temperature. The time dependence of the thermal lens signal of pyridazine in the solid phase is very different from that in a fluid medium. These results are discussed.

The role of free volume in the twisted intramolecular charge transfer (TICT) emission of dimethylaminobenzonitrile and related compounds in rigid polymer matrices

Abstract The amount of free volume present in a polymer matrix represents a driving force toward twisted intramolecular charge transfer (TICT) emission of p-dimethylaminobenzonitrile (DMABN) and related compounds. The intensity of the TICT band for these compounds in PVC (poly(vinyl chloride), PVA (poly(vinyl alcohol)), PHEMA (poly(hydroxyethyl methacrylate)) and PMMA (poly(methyl methacrylate)) was found to increase in this order, which is consistent with the increased free volume present in the same sequence. This rules out specific solute-solvent interactions as being responsible for the TICT emission in PVA polymer matrices.

Fluorescence decay characteristics of 4-dimethylaminobenzonitrile in different polymer matrices: a time-resolved study in the nanosecond range

Abstract The fluorescence decay curves of 4-dimethylaminobenzonitrile (DMABN) in different polar protic and aprotic polymer matrices are nonexponential. The lifetimes of the twisted intramolecular charge transfer (TICT) band are in the nanosecond range. With nanosecond time-resolved fluorescence spectroscopy dual fluorescence was observed for DMABN in a poly (vinyl alcohol) (PVA) polymer matrix at room temperature. These observations contradict results obtained by Cazeau-Dubroca and coworkers who report lifetimes of the TICT band of DMABN in PVA polymer matrices of the order of 1 s and claim the emission is an α-delayed fluorescence. Free volume effects are shown with 1,1,4,4-tetraphenylbutadiene (TPB) in PVA matrices.

Red edge effect (REE) phenomena of flexible solute molecules as a probe for polymer rigidity and/or free volume

Abstract The fluorescence spectra of the tert-butyl ester of 9-anthroic acid (9TBA) in two PVA (poly(vinyl alcohol)) polymer matrices of different molecular weights are different and indicate media of different rigidity. 9TBA also undergoes different edge excitation red-shifts in these PVA polymer matrices and is attributed to a decrease in the free volume in the higher molecular weight matrix. Comparison of the red edge effect (REE) observed for 9TBA in PVA (molecular weight 88000) polymer matrix with the REE observed in polymethylmethacrylate (PMMA) and in poly(hydroxyethyl methacrylate) (PHEMA) polymer matrices is used to establish that the free volume in PVA (88000) is smaller than in PHEMA or PMMA.

The red edge effect as a tool for investigating the origin of the anomalous fluorescence band of 9,9′-bianthryl in rigid polar polymer matrices

Abstract The excitation wavelength dependence of the fluorescence of 9,9′-bianthryl (BA) in polar polymer matrices at room temperature is attributed to the presence of different conformers (angular distribution of the two anthryl moieties) trapped in sites with different solvation and absorbing at different energies. The broadening of the fluorescence at the red edge excitation of BA in polar polymer matrices is due to a twisted intramolecular charge transfer (TICT) band. This case of the red edge effect (REE) exhibited by BA represents a converse example to the REE observed for flexible molecules with one fluorescence band and a sharpening of the fluorescence.

The quantum yield of triplet formation and triplet lifetime of pyridine in the liquid phase by the two-photon-excited time-resolved thermal lens method

Abstract The quantum yield of triplet formation and the triplet lifetime of pyridine are measured for the first time in the liquid phase using the two-photon-excited time-resolved thermal lens method. The triplet lifetime (1.0 μs) is very short and the quantum yield of the triplet formation (0.9) is large. These results are discussed in comparison with the same parameters reported for the gas phase.

Observation of transient absorption by using the thermal lens method

The application of thermal lens spectroscopy to the absorption measurement of the transient species is demonstrated. The unique advantages of this method are discussed.

The exchange interaction in the radical pair in 2-propanol solution as studied by the CIDNP multiplet pattern

Abstract The exchange interaction in the radical pair in homogeneous solution has been investigated by using the CIDNP method. The experimental observations of the multiplet pattern were compared with the theoretical simulations in which the exchange integral was a variable parameter. The results show that 2-propanol is a unique solvent in that the exchange integral in the radical pair in this solvent is large.

Picosecond laser spectroscopy of poly(methylphenylsilylene). Confirmation of previous assignment of the broad band

Abstract Photoluminescence of poly(methylphenylsilylene) is investigated by picosecond laser spectroscopy. The sharp band at 350 nm decays with a lifetime of 70 ± 15 ps. The broad band in the 400-500 nm region first rises with a lifetime of 70 ± 15 ps and then decays with a lifetime of ≈ 600 ps. The agreement between the decay rate constant of the sharp band and the rise rate constant of the broad band unambiguously substantiates the previous assignment that the sharp and the broad bands are emissions from the 1 (σ, σ*) and 1 (σ, π*) states, respectively.