New Oligothienyl-Imidazo-Phenanthroline Chromophores for NLO Applications

Abstract

Abstract. A new series of oligothienyl-imidazo-phenanthrolines 3 were synthesised in good to excellent yields by condensation of 5,6-phenantroline-dione 2 with formyl-thiophene derivatives 1 in the presence of ammonium acetate in glacial acetic acid. Furthermore, their solvatochromism and molecular optical nonlinearities were determined and comparatively studied. The experimental results indicate that phenanthrolines 3, due to their moderate solvatochromic properties and good optical nonlinearities, could be used as suitable probes for the determination of solvent polarity and as nonlinear optical materials.Introduction Donor-acceptor π-conjugated organic materials have received much attention as they offer many new possibilities for devices combining unique optical, electrical and mechanical properties. In particular, chromophores bearing low aromaticity heterocycles along the conjugation path have been investigated and are considered as the most suitable for these applications. Heterocyclic imidazole based chromophores have received increasing attention due to their distinctive linear and nonlinear optical properties and also due to their excellent thermal stability in guest-host systems and good miscibility with high performance polymers. The imidazole ring can be easily tailored to accommodate functional groups, which allows the covalent incorporation of the NLO chromophores into polyamides leading to NLO side chain polymers [1][2][3][4][5][6][7][8][9][10]. New material properties can be achieved when new conjugated systems are composed by different heterocyclic nuclei which allow the fine tuning of important physical and/or photophysical properties. Oligothiophenes behave as very efficient electron relays almost comparable to polyenes, because of the lower resonance energy of thiophene compared to that of benzene, and have been shown to give larger contributions to β. Oligophenylenes attain a rapid saturation beyond the terphenyl unit, whereas oligothiophenes have a strong tendency to increase β with increasing number of thiophene units. Aside from the electron transmission efficiency, another merit of oligothiophenes is their inherent stability from which thiophene-based Donor (D) -Acceptor (A) chromophores should benefit [11].