Photophysical characteristics of directly linked pyrene-dimethylaniline derivatives

Experimental and theoretical investigations of the spectroscopic properties have been carried out on three charge-transfer model systems, covalently linked donor-acceptor compounds of the type pyrene and derivatives of N,N-dimethylaniline (dimethyl(4-pyren-1-ylphenyl)amine (PyDMA), dimethyl(3-methyl-4-pyren-1-ylphenyl)amine (PyMDMA), and (3,5-dimethyl-4-pyren-1-ylphenyl)dimethylamine (PyDMDMA)). Comparing stationary absorption and emission spectra as well as fluorescence lifetimes in different solvents, one can show that small chemical changes such as substitution of ortho-hydrogens by methyl groups on the DMA moiety introduces dramatic effects in spectroscopic and kinetic behavior. On the basis of infrared measurements and quantum chemical calculations, the experiments are interpreted within a statistical framework, with particular emphasis on the discussion of preferred large amplitude motion (twist angle) and pyrene-specific vibronic coupling.