The dependence of the fluorescence constants kfnand the adiabatic twisting constants ktpof the S1-State upon the solvent polarity, the capacity of hydrogen-bonding, as well as the solvent viscosity, were investigated for donor-acceptor substituted trans-stilbenes [4-dimethylamino-4′-cyano-stilbene (1 g), 4-dimethylamino-4′-diphenylphosphinyl-stilbene (1 b), 4-dimethylamino-4′-brom-stilbene (1 h) and 4-dimethylamino-4′-methoxistilbene (1 k)] by using the multiparameter model. An increase of the solvent polarity results in the decrease of the fluorescence rate kfnfor all these compounds. The specific interaction between the strongly polar stilbenes such as 1 g and 1 b and a solvent leads to additional decrease in kfnbut in the case of a relatively weak polar compound 1 k to its growth. The linear combination of universal and specific solvent-solute interactions yields distinct relations for ktp. Both interactions have an influence on ktpfor 1 g, 1 b, and 1 k to an equal degree. The twisting observed for 1 g and 1 b due to the interaction with solvent is hindered, however it is being supported for 1 k. The influence of the investigated small range of viscosity on ktpat simultaneous variable solvent polarity (pure solvent) is only visible for the weak polar 1 k. In the other cases the effect of solvent-polarity is predominant. The viscosity dependence of ktpwas also experimentally proved for 1 g, 1 b and 1 k by applying the obtained different dimethylformamid-acetonitril mixtures. According previous results the radiationless deactivation process is caused by twisting around ethyl-bonding, therefore ktpevidently decreases with an increase of viscosity.
- Deactivation of S-state
- Influence of substituents, solvent polarity and viscosity
- Trans-cis Photoisomerization