Abstract

Organic molecules have been extensively studied in view of their potential applications for second-harmonic generation and electrooptic modulation in nonlinear optics.¹ Molecules bearing a donor- acceptor (or push-pull) substituted π electron system can yield significant quadratic hyperpolarizabilities β. In addition, early experimental studies on para disubstituted polyenic systems have shown superlinear dependences of β with the length of the conjugation path linking the electron-donating and electron-accepting end groups.²⁻⁴ Also semiempirical calculations conducted on two series of push-pull polyene series predicted a rapid increase in β with the number n of double bonds, the effect per unit volume saturating beyond n = 20.⁵ Clearly longer push-pull polyenes are relevant candidates for the design of compounds with dramatically enhanced nonlinearities.

© 1994 IEEE