Polyhedral-based nonlinear optical materials. 2. Theoretical investigationof some new high nonlinear optical response compounds involving polyhedralbridges with charged aromatic donors and acceptors

A theoretical study of several new classes of polyhedral-based molecules ha s shown that these species display large calculated nonlinear optical respo nses. These new classes of molecules are based on charged aromatic subunits connected through polyhedral cluster bridges, such as closo-[1-(C7H6)-12-( C5Me4)C2B10H10]. These compounds show calculated first hyperpolarizabilitie s (beta) ranging from 6.5 to 8413.9 x 10(-30) cm(5) esu(-1). A basis for un derstanding the origin of these large responses is proposed based on the tw o-state model and consideration of the orbital and electronic features of t he molecules. In general, the highest occupied molecular orbitals for these species are localized on the aromatic donor rings, such as the cyclopentad ienyl system, while the lowest unoccupied molecular orbitals are largely on the aromatic acceptor rings, such as the tropylium system. The electronic properties of these polyhedral-based systems appear to be significantly dif ferent from the analogous organic [5.6.7]quinarene system (tropyliumcyclope ntadienylbenzene). The organic quinarene appears to behave as a completely electron-delocalized system over all three rings while the polyhedral-based compounds can best, be described as consisting of two relatively independe nt, highly polarized regions.