The fluorescent state of cyano-substituted layered cyclophanes

Some cyano-substituted layered cyclophanes were studied by fluorescence and nanosecond laser photolysis in various solvents. Although almost no characteristic solvent effect was observed in the case of III_c, the results on II, III_s, and III_e are summarized as follows, (i) The fluorescent maxima shows a considerable red shift with increasing solvent polarity. A deviation from the modified Lippert-Mataga equation is observed, (ii) The fluorescence quantum yield decreases as the solvent polarity is increased. On the other hand, the solvent dependence of the fluorescence lifetime is diverse. (iii) In the case of some cyclophanes the S_n ← S₁ absorption spectra in toluene are different from those in acetonitrile. On the basis of these results it is concluded that the electronic structures of the excited cyclophanes are changed depending on the solvent polarity. The results were compared with those on other excited CT systems and are discussed in general.