Merritt C. Helvenston

NLO studies of a novel phenothiazine self-assembled monolayer

The nonlinear optical behavior of self-assembled monolayer films of a new NLO-active molecule, PBSP, is characterized by second harmonic generation (SHG). PBSP contains a heterocyclic sulfonate head group and a highly polarizable chromophore. The films are synthesized by a nucleophilic substitution reaction on both sides of a quartz substrate that has been treated with a coupling layer. The addition of the chromophoric layer is monitored by AFM, FTIR and UV- visible spectroscopy, and SHG. The FTIR spectrum of the first layer shows weak methylene resonances, while the spectrum with the addition of the second layer shows much stronger methylene resonances and an amine resonance. The characterization of the film by SHG was done by rotating the film and generating Maker fringes. The polarization dependence of the SHG signal was also determined. The SHG signal after the nucleophilic reaction was an order of magnitude greater than before the reaction. The magnitude of the dominant element of the nonlinear susceptibility and the average molecular orientation angle of the chromophore were determined by modeling the Maker fringes and the polarization dependence of the SHG signal.