Journal of Sol-Gel Science and Technology 26, 967–970, 2003 c  2003 Kluwer Academic Publishers. Manufactured in The Netherlands. Entrapping of Push-Pull Zwitterionic Chromophores in Hybrid Matrices for Photonic Applications PLINIO INNOCENZI AND GIOVANNA BRUSATIN Dipartimento di Ingegneria Meccanica, settore materiali, Universit` a di Padova, via Marzolo 9, 35131 Padova, Italy ALESSANDRO ABBOTTO, LUCA BEVERINA AND GIORGIO A. PAGANI Dipartimento di Scienza dei Materiali, Universit ` a Milano-Bicocca, via Cozzi 53, 20125 Milano, Italy MAURO CASALBONI AND FELICE SARCINELLI Dipartimento di Fisica and INFM, Universit` a di Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Rome, Italy ROBERTO PIZZOFERRATO Dipartimento di Ingegneria Meccanica and INFM, Universit` a di Roma “Tor Vergata”, via di Tor Vergata 110, 00133 Rome, Italy Abstract. A new class of heterocycle-based push-pull chromophores showing enhanced nonlinear properties characterized by an aromatic and highly zwitterionic ground state and a quinoid/neutral excited state have been synthesized to be incorporated in sol-gel hybrid systems. This class of compounds shows very large first molecular hyperpolarizabilities (βµ as high as 27000 × 10 -48 esu) and is a promising candidate for photonic applications where large second order non-linearities are required. In spite of their very large hyperpolarizability and chemical and thermal stability, these chromophores are decomposed in presence of light and oxygen (photobleaching) and are sensitive to acidic environments due to the carbanionic nature of the donor moiety. A hybrid matrix, based on N -[(3- trimethoxysilyl)propyl]ethylenediamine and 3-glycidoxypropyltrimethoxysilane, has been specifically designed to allow the incorporation of such zwitterionic compounds assuring at the same time a good temporal stability of the optical properties. Amine functionalisation has been found very effective in reducing the photobleaching by acting on these chromophores via the singlet oxygen. Second harmonic generation has been observed on poled films, and an order parameter, , of 0.17 has been estimated. The nonlinear coefficient d eff of the samples has been thus estimated at a value two times larger than for d 11 of quartz that, from literature data, is about 0.335 pm/V. Keywords: hybrid, 3-glycidoxypropyltrimethoxysilane, second harmonic generation, poling 1. Introduction Poled organic-inorganic hybrid materials, where the nonlinear optical properties are added by organic hyperpolarizable chromophores covalently bonded to the matrix network, have attracted some attention as a suitable solid-state system for photonic devices [1–3]. These materials are an interesting alternative, because of their very peculiar properties, to organic polymers to fabricate photonics devices. They exhibit, in fact, a larger laser damage threshold, low optical propagation losses, high transparency and are very easily processed as films. A practical device requires in addition the incorporation of large amounts of NLO chromophores,