Novel linear and ladder polymers from tetraynes for nonlinear optics

The tetrayne monomer with urethane groups in substituents, i.e., hexadeca-5, 7, 9, 11-tetrayn- 1, 16-diyl bis(N-(butoxycarbonyl)methyl)carbamate, was synthesized so as to check the generality of the polymerization scheme observed in a dialkyltetrayne. It was confirmed that the polymerization behavior of this urethane monomer is just the same as the dialkyltetrayne: Namely, the monomer was polymerized by (gamma) -ray irradiation to give a linear polymer of the polydiacetylene with diacetylenic substituents (polymer I), and the following thermal polymerization of diacetylenic moieties in side chains estimated to give a ladder polymer of the di(polydiacetylene) (polymer II) in which two polydiacetylene backbones are conjugated. Though the third-order nonlinear optical susceptibilities of the polymer I were evaluated to be the same order of magnitude as those of the polydiacetylenes with aromatic substituents directly bound to the main chain, no detectable third harmonic generation was observed for the polymer II. This may be due to the disappearance of the excitonic absorption in polymer II, caused by deterioration of the crystallinity and/or instabilization of excitons.