Theoretical Prediction, Synthesis and Characterization of RSA Materials

We propose to synthesize and characterize by time resolved spectroscopy RSA compounds that have been structurally modified to maximize the ratio of excited state to ground state absorption cross sections over a broad visible range. The structuralmodifications will be made based on ab initio and semiempirical quantum mechanical predictions of excited state energetics and absorption intensities. The theoretical models will be developed by the Mark Ratner group at Northwestern, based on our priorcollaborations resulting in accurate prediction of triplet-triplet absorption energies in over 100 organic chromophores, in effect allowing a priori predictions of wavelength-dependent optical limiting curves in hypothetical molecules. Phase I will entailsynthesis of several derivatives of a promising RSA porphyrin, the experimental mapping of their energy levels and triplet state absorption spectra, and the use of the results to verify theoretical prediction of the substituent effects on these properties.Phase Ia and II will entail further refinements to the theory and its application to prediction of intersystem crossing rates to provide a package generally useful to Army researchers. This will permit us to design an optimized RSA compound which will besynthesized, characterized and implemented into solid state filter designs with acceptable optical damage thresholds. The general materials approach will enable rapid development of new optical limiting materials for the full range of threat wavelengths.The materials have government markets for sensor and eye protection and commercial markets as laser safety eyewear and as protection for cameras and optical instruments.