THEORETICAL PREDICTION AND SYNTHESIS OF NEW BICHROMOPHORE OPTICAL LIMITERS

Optical limiting is an approach to protecting the human eye and electro-optical sensors against laser damage. Required are weakly absorbing materials that are efficiently converted to strongly absorbing excited state(s) during a laser pulse and then decay to the ground state to provide continued optical transparency. We propose a program to develop bichromphores as optical limiting materials built from donor and acceptor moieties which are strongly coupled by an appropriate linking group. Structural control of the coupling will be employed to yield an intense triplet excited state absorption with a high degree of charge transfer character while the ground state absorption is localized and/or symmetry forbidden or has its maximum intensity out of the visible range. Molecular mechanics and electronic structure calculations (ab initio and semiemprical) will be employed to predict ground and excited state geometries, absorption spectra, intensities and lifetimes to guide the design of bichromophores, followed by synthesis of selected materials and their experimental evaluation as optical limiters. In Phase I we will establish the theoretical protocols, conduct calculations of ground and excited state spectra of several model bichromophores, and synthesize and evaluate one or more promising materials.