Study of Diacetylene Monomer and Polymer Monolayers Using Second- and Third-Harmonic Generation

摘要

Monolayers of several diacetylene monomers and polymers spread at the air-water interface have been studied using optical second-harmonic generation (SHG) and third-harmonic generation (THG). Owing to the centrosymmetry of the diacetylene core, SHG from these molecules arises mainly from their side groups. THG from a single monolayer of polydiacetylene is reported, to our knowledge, for the first time--the THG signal (in reflection) arising from the polydiacetylene monolayer is several times larger than that from the water subphase. THG was observed both when a polymer monolayer was spread directly and when a monomer monolayer was UV polymerized on the water surface. Values of the third-order nonlinearity of polydiacetylenes derived from these measurements are in agreement with earlier studies.