Poly(vinylpyridine) and Related Polymers as Guests for Organotransition-Metal-Based NLO Chromophores

We have investigated a set of three polymers functionalized by tungsten pentacarbonyl as a chromophore for second harmonic generation (SHG). Films were poled by the Corona poling method, and their second-order nonlinear responses were measured via in situ SHG while poling. It is found that poly(vinylpyridine) can be used as a probe to obtain the sign of the hyperpolarizability coefficient of the chromophores (β). These polymers all exhibit modest SHG properties. This raises several interesting theoretical and practical questions which are discussed: thermal stability, effect of a negative sign of β, importance of the chromophore dipole moment, and poling efficiency of chromophores based on tungsten pentacarbonyl. Relaxation mechanisms are also discussed in relation to the structure of the polymers backbone.