Nonlinear optical properties of π-conjugated compounds incorporating a saturated spacer group

We investigate theoretically the evolution, as a function of an applied external electric field, of the nonlinear optical (NLO) properties of a push-pull polyene molecule containing a saturated spacer group in the middle of the conjugated path; the role of the spacer group is to break the conjugation between the donor part and the acceptor part. As in the case of fully conjugated polyenes, we obtain derivative relationships that relate the molecular dipole moment and the polarizabilities at different orders, as a function of the external field. As the spacer that breaks the conjugation gets longer, the polarizabilities are calculated to be very high around the critical field that needs to be applied to lead to a full delocalization of the charge from the donor segment to the acceptor segment.