Development of molecules for all-optical switching devices

The prospects for developing efficient molecular devices for all-optical switching are discussed on the basis of measurements of the second molecular hyperpolarizability coefficient, gamma, responsible for third harmonic generation. More than twenty structurally different organic compounds comprising organic metal complexes, polyenes, cyanines, and derivatives of triarylmethyl cations have been examined. The dependence of gamma on the number of pi-electrons in the nonlinear chromophore leads to a classification of the data in four categories; (i) the polyene like, (ii) the cyanine-like, (iii) the bis-1,2-dithiole metal complexes, and (iv) a new category comprising molecules with significant ligand-to-metal or other ''periphery-to-center'' charge transfer transitions. Values of gamma as high as 3 x 10(-32) esu are reported in this new category. The importance of changes in higher multipole moments such as quadrupole and octupole moments upon electronic excitation is addressed. Strategies for improved molecular and materials design are discussed.