Second-harmonic generation from Langmuir-Blodgett film of cyclic peptide carrying two disperse red 1 on fused quartz surface.

Cyclic octapeptide carrying one or two nonlinear optical chromophores, disperse red 1 (DR-1), was synthesized and immobilized on a substrate to attain an active surface for second-harmonic generation (SHG). Each cyclic octapeptide was transferred on a fused quartz substrate by the Langmuir-Blodgett (LB) method to afford a uniform monolayer. Infrared reflection-absorption spectroscopy of the LB monolayer revealed that the cyclic skeleton lay roughly flat on the surface. The SHG intensity from the monolayer of the cyclic peptide with two DR-1 units was stronger than that from that with one DR-1 unit. The difference is discussed in terms of molecular orientation and surface density of the active chromophores. The cyclic peptide is shown here to be an effective scaffold to modify a substrate surface with functional groups of a monolayer with taking stability of the monolayer and orientation of the functional group into consideration.