Energy gap model

Some pseudoazulene systems show weak fluorescence (measured for 26, 27, 33, 39, 40, 44, 56, and 68)." 2 With the exception of pseudoazulenes 68 and 56, the emission by the other systems is due to the transition S2- So. Thus, with respect to fluorescence spectra, many pseudoazulenes show essentially the same properties as azulenes. The quantum yields of fluorescence are very low (between 10 and 10 ), They are markedly dependent upon the energy gap (S1-S2) and the flexibility of the pseudoazulene systems. The fluorescence quantum yields increase when additional benzene rings are introduced onto the uncondensed ring skeletons of the pseudoazulene systems, A slight increase in quantum yields is also observed if halides or phenyl groups are introduced. To explain this anomalous fluorescence the energy-gap model and a quantum chemical model have been invoked however, neither could explain all effects, Hitherto, no other luminescence spectra (particularly Sj Sq fluorescence and phosphorescence) have been observed for pseudoazulenes... 

Figure 24.B1 He- -Qj photodissodation rates. A semi-Log plot is used foLLowing the energy gap model. Here, n indicates the vibrational quantum number of the van der Waals complex. Reproduced from Cline etal, J. Chem. Phys., 1986, 84 1165, with permission of the American Institute of Physics...

Energy Gap Model of Glass Formers Lessons Learned from Polymers... 

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