The Effect of Conjugation Length and Electron Donor Groups on the Second Order Nonlinear Polarizability of Cyano Substituted Aromatic Molecules

Abstract

Second order nonlinear polarizabilities, α⁽²⁾, were measured for various cyano-substituted aromatic (phenyl, biphenyl, terphenyl and phenylpyrimidine) molecules. The largest nonlinearity was found in cyano-biphenyl compounds, indicating that ring twisting may be causing a decrease in terphenyl nonlinear polarizability. Electron donating substituent effects were demonstrated by comparison of the nonlinearity of alkyl and alkoxy cyanobiphenyls. In all cases α⁽²⁾ was determined from analysis of the optical second harmonic generation from a monolayer of amphiphilic molecules spread at the air/water interface.