Solvatochromism as an efficient tool to study N,N-dimethylamino- and cyano-substituted π-conjugated molecules with an intramolecular charge-transfer absorption

A representative data set has been gained by the measurement of the electronic absorption spectra of 12 systematically selected push–pull systems with an intramolecular charge-transfer (CT) absorption and the general structure D–π–A (D = donor, A = acceptor) featuring electron-withdrawing CN groups, electron-donating N(CH3)2 groups, and various π-conjugated backbones in 32 solvents with different polarities. The longest-wavelength absorption maxima λmax and the corresponding wavenumbers were evaluated from the UV/Vis spectra measured in 32 well-selected solvents. The D–π–A push–pull systems were further characterized by quantum-chemical quantities and simple structural parameters. Structure–solvatochromism relationships were evaluated by multidimensional statistic methods. Whereas solvent polarizability and solvent cavity size proved to be the most important factors affecting the position of λmax, the solvent polarity was less important. The most important characteristics of organic CT compounds are the energy of the LUMO, the permanent dipole moment, the COSMO (COnductor-like Screening MOdel) area, the COSMO volume, the number, and ratio of N,N-dimethylamino and cyano groups, and eventually the number of triple bonds (π-linkers). A relation between the first-order polarizability α, the longest-wavelength absorption maxima λmax, and the structural features has also been found. The higher-order polarizabilities β and γ are not related to the observed solvatochromism. Copyright © 2010 John Wiley & Sons, Ltd.