THEORETICAL-STUDIES ON THE ELECTRONIC-STRUCTURE AND NONLINEAR PROPERTIES OF DICYANOMETHYLENE SUBSTITUTED SQUARAMIDES, CROCONAMIDES AND RHODIZONAMIDES

The structure and dipole moments of squaramides, croconamides and rhod izonamides, and their derivatives containing the dicyanomethylene grou p, have been calculated using the AM1 and ab initio 3-21G methods. The molecular hyperpolarisabilities and dipole moments of these structure s calculated using a semi-empirical sum-over-states method are predict ed to increase with increasing ring size and increasing substitution b y the dicyanomethylene group. 1,2,3-Tris(dicyanomethylene)croconamide has a calculated frequency dependent hyperpolarisability and dipole mo ment which exceed the values obtained for typical donor-acceptor azobe nzenes, and shows potential as a new material for electro-optic modula tion.