The Photochemistry of Organic Materials for Photonic Devices

Optically active organic chromophores have attracted much interest in recent years for their potential for use in photonic devices. Chromophores such as compound (1) have been found to have a very high second order nonlinear susceptibility ( β ) value of 650 × 10⁻³⁰esu in dimethyl formamide.¹ The performance of 1 in a polymer film is much lower than this due to the formation of aggregates which hinder the poling process necessary to ensure a noncentrosymmetric arrangement of the molecules in order to display second order nonlinear behaviour. The molecular aggregation behaviour of a set of second order nonlinear compounds based on compound 1 have been studied in this thesis. These compounds share the backbone shown in figure 1 with pendant groups added to the R₁ R₂ and R₃ positions, with the aim of finding substituent groups that can be added to the optically active merocyanine backbone that reduce the aggregation and increase the solubility of the compounds. This in turn will make them more suitable for use in photonics devices. It was found that a C₁₁H₂₃ alkyl chain added to the R₃ position made the largest contribution to decreasing aggregation. Bulky groups on the R₁ and R₂ positions also reduced aggregation. As a result compounds 5 and 8, with R₃ = C₁₁H₂₃ and bulky groups attached displayed the least aggregation of the compounds studied. ¹ See Figure 1 (pg. i): Merocyanine backbone with substituent positions marked.