Stronger acceptors can diminish nonlinear optical response in simple donor-acceptor polyenes

There has been much recent effort in the design of optimal chromophores for second-order nonlinear optical (NLO) applications. Most studies of organic molecules have focused on donor-acceptor π-conjugated molecules containing aromatic groups. We will show that the NLO response of aromatic donor-acceptor chromophores is dramatically different than their simple polyene analogs. Although there have been several computational studies of the first hyperpolarizability (β) of the simple organic donor-acceptor chromophores, the polyenes, few molecules in this class have been studied experimentally. These molecules are the prototypical conjugated donor-acceptor chromophores and as such can serve as a base line reference for both experimental and theoretical NLO structure/property relationships. Accordingly, we report the results of electric-field-induced second-harmonic generation (EFISH) studies of simple donor-acceptor polyenes as a function of donor and acceptor strengths and of molecular length