Push-Pull Porphyrins as Nonlinear Optical Materials

Due to their potential applications for optical communications, data storage, and electrooptical signal processing, molecules with nonlinear optical (NLO) properties have been extensively investigated.’ As part of our interest in porphyrins and metalloporphyrins as photoresponsive2 and field-responsive material^,^ we have synthesized a series of “push-pull” porphyrins containing both donor and acceptor substituents and have examined their NLO properties. The enhancements in molecular hyperpolarizabilities in previous organic systems have relied on donoracceptor interactions along one-dimensional pathways; our porphyrinic compounds are prototypes of donor-acceptor interactions in two dimensions. Porphyrins with their large a-conjugated system provide a versatile synthetic base to create effective intramolecular charge transfer (CT). As shown in Figure 1, the difunctionalized tetraarylporphyrins with nitro groups (n) as electron acceptors and amino groups (a) as electron donors have been prepared. The synthesis of H2(an3Por), H2(cis-a2n2Por), and H2(a3nPor) does not involve the traditional crossed-condensation for multisubstituted porphyrins: which are usually isolated only in low yields (<5%). Instead, H2(n4P04), H2(an3Por), H,(trans-a,n,Por),