Donor-pi-acceptor structure between Ag nanoparticles and azobenzene chromophore and its enhanced third-order optical non-linearity

An amorphous silica hybrid film containing covalently linked azobenzene chromophores and Ag nanoparticles was synthesized by a one-step sol-gel route in the presence of amino trialkoxysilane (APTES). The electron transfer from the N-containing groups in the APTES and azobenzene molecules, which are chemisorbed onto the surface of Ag nanoaprticles, makes the Ag nanoparticles negatively charged. Subsequently, a new D-pi-A electron structure between the Ag nanoparticles and the N-containing groups/azobenzene chromophores is created. The enhanced internal electric field in the nanoparticles and the strengthened and extended pi-conjugation in the new D-pi-A electron structure, lead to the large enhancement of optical non-linearity of the hybrid films.