Coumarin 153 emission thermochromism studied in non-specifically and specifically interacting solvents

We report a study of the thermochromic shifts observed for coumarin 153 (C153) emission spectra in several selected chloroalkanes and several solvents potentially specifically interacting with the probe. It has been found that the shifts observed in five 1-chloroalkanes can be successfully predicted using the McRae molecular interaction model [E.G. McRae, J. Phys. Chem. 61 (1957) 562]. However, the shifts observed in two other chloroalkanes have been found not to correspond to the value, which can be derived using the same C153 molecular parameters (dipole moments, molecular radius and gas phase emission spectrum position) as in the analysis of shifts in 1-chloroalkanes. This observation suggests that 1-chloroalkanes may interact specifically, contrary to what was assumed in our previous papers. The temperature dependence of changes in the energy of these specific interactions, after C153 excitation, also in the solvents known to interact in this way, is discussed in view of the thermochromic results reported in this paper and literature data. We show that even for C153, one of the most often studied probe, one cannot definitively state in what kind of specific interactions it takes or does not take part.