EVALUATION OF OPTICAL NONLINEARITIES IN CALIXARENES

The structure and dipole moments of a series of donor acceptor calixar enes (1-3) containing from four to six aromatic rings have been calcul ated in their cone conformations using the AM1 method. The nonlinear o ptical properties of these systems have been evaluated in terms of the ir first hyperpolarizabilities using a semiempirical sum-over-states a pproach. All of the calixarenes studied are predicted to have large di pole moments, but their hyperpolarizabilities are critically dependent on the number of excited states included in the evaluation and on the orientation of the donor substituent. An increase in calixarene ring size has only a modest effect on the electronic properties. The limite d space at the head of the calix(4)arene ring forces the substituents in both the methoxy (Ic) and methylamino (le) derivatives into unfavor able conformations; which substantially reduces the conjugation betwee n their lone pair electrons and the pi-electron System of the respecti ve aromatic rings to give poor hyperpolarizabilities. When the lone pa ir electrons of the amino derivative are locked into an orthogonal pos ition with respect to the aromatic ring plane by appropriate bridging alkyl groups, the resulting structure (If) shows considerable potentia l as a nonlinear optical material for poled polymer films with an extr emely large dipole moment of 24.4 D and a calculated hyperpolarizabili ty of 49.9 x 10(-30) cm(5) esu(-1).