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Fluorescence excitation spectra and fluorescence lifetimes at single vibronic levels in the S 1 state have been observed for jet-cooled pyrene. The fluorescence lifetimes at the zero-vibrational levels of the S 1 1 B 3 u states of pyrene- h 10 and pyrene- d 10 are 1480 and 1470 ns, respectively, and the relaxation is considered to be dominated by the radiative process. For some vibrational levels, however, the lifetimes are remarkably shorter such as 765 ns at the 221 vibronic level of pyrene- h 10 ( ν 22 ( b 1 g ); C–H bending and skeletal deforming mode), indicating that nonradiative transition occurs at a specific vibrational level. In this study, we demonstrate that the main process is internal conversion to the S 0 1 A g state caused by nonadiabatic vibronic interaction via b 3 u promoting modes.

We observed fluorescence excitation spectra and dispersed fluorescence spectra for single vibronic level excitation of jet-cooled perylene-h 12 and perylene-d 12, and carefully examined the vibrational structures of the S0[1] A g and S1[1] B 2u states. We performed vibronic assignments on the basis of the results of ab initio calculation, and found that the vibrational energies in the S1 state are very similar to those in the S0 state, indicating that the potential energy curves are not changed much upon electronic excitation. We conclude that the small structural change is the main cause of its slow radiationless transition and high fluorescence quantum yield at the zero-vibrational level in the S1 state. It has been already reported that the lifetime of perylene is remarkably short at specific vibrational levels in the S1 state. Here, we show that the mode-selective nonradiative process is internal conversion (IC) to the S0 state, and the ν16(a g ) in-plane ring deforming vibration is the promoting (doorway) mode in the S1 state which enhances vibronic coupling with the high-vibrational level (b 2u ) of the S0 state.

The two-color fluorescence depletion process of Rhodamine 6G in PMMA matrixes was investigated using nano- and picosecond lasers. Erase-lasers of 1064 and 599 nm depleted the fluorescence from the S1 state. Fluorescence depletion with 1064 nm was analyzed by the up-conversion from state S1 to S2, while that with 599 nm was simulated based on both the up-conversion and the stimulated emission. A three-state model describes this process due to a nanosecond laser well, while it could not reproduce that by picosecond lasers. Significant contributions of vibrational relaxation in S1 and re-absorption from S0 are suggested in the picosecond region.

Rotaviruses were detected via electron microscopy in fecal specimens collected from school children during an outbreak of diarrhea and from a sporadic case in 1993 in Japan. All of the viruses were found to belong to human group C rotavirus by reverse passive hemagglutination assay (RPHA). These viruses replicated well in a human colon carcinoma (CaCo-2) cell line cultured in the presence of trypsin (4 micrograms/ml). This report demonstrates that human group C rotaviruses can be propagated efficiently in a cell line cultured in the presence of trypsin. The infected cells did not show any apparent cytopathic changes. However, virus was detected in the cell cytoplasm by immunofluorescence (IF) staining and in the culture supernatant by RPHA. On the basis of immune electron microscopy (IEM), virus particles collected from infected CaCo-2 cell cultures were confirmed to aggregate specifically with anti-human group C rotavirus antibody. The electrophoretic patterns of RNA segments extracted from viral particles found in the fecal specimens or infected cells were identical to those of human group C rotavirus. These results indicated that human group C rotaviruses were the causal agent of the diarrhea outbreak.

For the three azabenzenes pyridine, pyrazine and pyrimidine, quantum yields for fluorescence and intersystem crossing have been measured in the vapour phase as a function of the excitation energy, ranging from the zero-point level of S1(n, π*) to the higher vibrational levels of S2(π, π*). The picosecond fluorescence lifetimes have also been measured by exciting the molecules at various wavelengths. For all three azabenzenes a particularly fast non-radiative decay channel has been found. The appearance of this new decay channel has also been demonstrated by direct measurement of the picosecond lifetime. In the lower excitation-energy region of the S1â†�S0 transition the intersystem-crossing process is dominant, whereas above the excitation-energy threshold the non-radiative transition is governed by this decay channel. These new decay channels in azabenzenes may be related to photoisomerization processes, which are known to proceed by irradiation of u.v. light corresponding to the S2â†�S0 absorption transition. The discussion is developed in relation to “channel three” in the parent hydrocarbon, benzene.