Polydiacetylenes for photonic application: chemical modulation of optical properties

Highly soluble alkyl-substituted derivatives of the polycarbazolyldiacetylene, with a particularly large value of the off-resonance third-order non-linearity have been obtained in our laboratories. In order to investigate the role played by the electron-donating character of the carbazolyl groups on the optical and electronic properties of the material, we have synthetized diacetylenic monomers carrying electron-withdrawing acyl-substituents on the carbazolyl rings. Acyl-substituents CH3(CH2)nCO– with n=10,14,16 were introduced. The polymers derived by thermal polymerization of the microcrystalline monomers are sparingly soluble and only very dilute solutions are stable at room temperature. However, thin films of the polymers of excellent optical quality are obtained by solution casting of a monomer layer on various substrates, followed by thermal polymerization. These films have been characterized by spectroscopic techniques and by preliminary measurements of third-order susceptibility. Particular attention has been dedicated to the study of both their thermal and photochemical behavior.