HIGHLY DIPOLAR, OPTICALLY NONLINEAR ADDUCTS OF TETRACYANO-P-QUINODIMETHANE - SYNTHESIS, PHYSICAL CHARACTERIZATION, AND THEORETICAL ASPECTS

A new series of nonlinear optical molecules are described where the gr ound state polarization is predominantly zwitterionic when the molecul es are dissolved in solution. The molecules, which are derived in gene ral from facile reactions between tertiary amines and tetracyano-p-qui nodimethane (TCNQ), are of a type where the stabilization of the charg e-separated ground state is favored by an increase in aromaticity over the neutral, quinoidal forms of the molecules. The measured second-or der optical nonlinearity of one in the series has been measured by hyp er-Rayleigh scattering and a figure of merit value, mu beta(0), being the product of the dipole moment and static first hyperpolarizability, is found to be 9500 x 10(-48) esu. This value, which is higher than m ost other reported values, is taken from studies in chlorinated solven ts of relatively low polarity, but the discussion emphasizes the evolu tion of eta beta(0) with solvent polarity, showing that even higher va lues could be expected with only modest increases in the polarity of t he surrounding medium. The analysis of experimental data taken during dipole moment studies is thoroughly examined, and it is concluded that full account must be taken of the molecular shape to correlate the re sults with theoretical calculations. An ellipsoidal reaction field mod el is preferred for these highly one-dimensional molecules having stro ngly anisotropic polarizabilities.