Supersonic jet and solution studies of intramolecular complexes with TICT formation mimicking solute-solvent interaction

Three ester derivatives of N,N-dimethylaniline have been studied, which pos sess a flexibly linked intramolecular hydroxyl group amenable to mimic 1:1 complexation of donor-acceptor molecules with solvent molecules. The supers onic jet fluorescence excitation spectra indicate a small redshift for thes e intramolecularly complexed compounds with respect to the noncomplexed mod el compounds giving evidence for the intramolecular complexation by hydroge n bond formation at the ester group. The dispersed fluorescence spectra bro aden upon an increase in the excitation energy. Semiempirical simulated ann ealing calculations using AMPAC/AM1 show that there exist many possible con formations of similar energy for the molecule, with H bonding at the carbon yl or alkoxy oxygen in the most stable conformer. A shift in the carbonyl v ibrational frequencies is consistent with a carbonyl self-complexed species . The dual fluorescence observed in acetonitrile as solvent is very similar f or all three compounds, with a slight redshift of the long wavelength charg e transfer (CT) band for the complexed species with respect to the uncomple xed one consistent with the twisted intramolecular charge transfer model. T he absence of a clear CT band in spite of complete intramolecular hydrogen bond complexation in alkanes is interpreted as evidence that formation of a specific solute-solvent complex alone is not sufficient to create the larg e anomalous CT band observed for N,N-dimethylaminobenzonitrile in polar and mixed polar/nonpolar solvents. (C) 2000 Elsevier Science B.V. All rights r eserved.