THE ROLE OF LONDON FORCES IN DEFINING NONCENTROSYMMETRIC ORDER OF HIGH DIPOLE-MOMENT HIGH HYPERPOLARIZABILITY CHROMOPHORES IN ELECTRICALLY POLED POLYMERIC THIN-FILMS

Graphs of second harmonic generation coefficients and electro-optic co efficients (measured by ellipsometry, attenuated total reflection, and two-slit interference modulation) as a function of chromophore number density (chromophore loading) are experimentally observed to exhibit maxima for polymers containing chromophores characterized by large dip ole moments and polarizabilities. Modified London theory is used to de monstrated that this behavior can be attributed to the competition of chromophore applied electric field and chromophore-chromophore electro static interactions, The comparison of theoretical and experimental da ta explains why the promise of exceptional macroscopic second-order op tical nonlinearity predicted for organic materials has not been realiz ed and suggests routes for circumventing current limitations to large optical nonlinearity, The results also suggest extensions of measureme nt and theoretical methods to achieve an improved understanding of int ermolecular interactions in condensed phase materials including materi als prepared by sequential synthesis and block copolymer methods.