Triphenylamine-Cored Bifunctional Organic Molecules for Two-Photon Absorption and Photorefraction

Multiarmed nonlinear optical (NLO) molecules containing triphenylamine as a core and 4-(2-ethylhexylsulfonyl)benzene-(1E)-2-vinyl group or 4-{2-[4-(2-ethylhexylsulfonyl)phenyl]-(1E)-vinyl}benzene-(1E)-2-vinyl group as arms were synthesized (STEH series and SSEH series, respectively). Because triphenylamine linked to the sulfonylated stilbenic arms provided effective push−pull NLO structure and strong 2-D charge transfer, they were capable of both two-photon absorption (TPA) and photorefraction. Effective TPA cross sections of these molecules were as high as 0.94 × 10 - 46 cm 4 ·s and significantly enhanced as the number of arms and conjugation length increased. One- and two-armed STEH molecules (STEH1 and STEH2) showed moderate two-beam coupling gain coefficients (13.4 cm - 1 at 45 V/μm and 17.4 cm - 1 at 55 V/μm, respectively) and distinct diffraction efficiency (0.45% at 40 V/μm and 0.55% at 55 V/μm). On the other hand, the centrosymmetric three-armed STEH molecule exhibited no photorefraction at all. It is importantly claimed that the multiarmed bifunctional molecules of this work are easily fabricated into optically clear amorphous films by themselves, which is a key advantage toward potential applications such as solid-state optical limiting devices and two-photon excited photorefractive materials.