An Alternative Route Based on Acid−Base Hydrolytic Chemistry to NLO Active Organic−Inorganic Hybrid Materials for Second-Order Nonlinear Optics

An alternative approach, based on simple acid−base hydrolytic chemistry, to prepare organic−inorganic composites is reported. In these hybrid materials, NLO-active chromophores such as Disperse Red 19, a pyridinium salt based dye, and 1-amino-4-nitrobenzene are covalently locked into silica networks. The resulting hybrids are soluble and offer ease of processibility in the preparation of good-optical-quality thin films. Network materials that are akin to the traditional sol−gel approach are also prepared from the monofunctional NLO chromophore DR1 and, as expected, are found to be insoluble. Physical properties of the NLO chromophore-incorporated hybrids can be tailored by changing the molar amounts of chromophores and water, and the type of chromophore. High thermal stability and glass-transition temperatures of these hybrids offer effective electric-field poling at high temperatures and long-term temporal stabilities of the second-harmonic-generation signals at room temperature and at 80 °C. The χ(2) values for the networks were found to be in the range of (1.2−37) × 10-8 esu.