THE EXCITONIC STRUCTURE AND EXCITED STATES DYNAMICS OF AZULENES

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It is expected that azulene forms the excimer easily because of the large dipole moment. However, the excimer and the dimer have never been reported. Azulenes are also well known to emit anomalous S_2 fluorescence contrary to Kasha's rule. We synthesized azulene cyano-derivatives that have larger dipole moment. The fluorescence spectra in solution, crystal and supersonic jet were observed in order to compare with the fluorescence and the relaxation dynamics of azulene.S_1 fluorescence was first observed in 1-cyanoazulene solution, while the quantum yield of S_2 fluorescence decreased to one tenth of azulene. We discussed these results in relation to the energy gap law.In crystal, the excimer fluorescence of azulene, 1-cyanoazulene and 2-cyanoazulene were observed in 420nm region. However, we could not detect the excimer fluorescence in solutions and a supersonic jet. It was suggested that the excimer formation is very difficult except in crystal. These results are characteristic in azulenes in contrast to other aromatic compound.Hole burning spectra of cyanoazulenes were measured in order to elucidate the dynamics from S_1. The S_1 life time was 1.8ps and 1.0ps in 1-cyanoazulene and 2-cyanoazulene, respectively. The later internal conversion in 1-cyanoazulene was related with the finding of S_1 emission.The photophysical properties of methyl- and phenyl-azulene are also investigating to elucidate the effect of electron donating group.