New Electron Acceptor for the Control of Crystal Structures and the Generation of High Optical Nonlinearities

ABSTRACTCyclobutenedione (CD) as a new electron acceptor for second order nonlinear optical materials is reported. After syntheses and evaluation of new materials containing CD, it is observed that CD is not only a strong electron acceptor to enhance second order molecular hyperpolarizability (β), but also the first substituent to control the molecular orientation in crystals. Compared with nitro (NO2) subsutitent, CD is shown to be advantageous in higher molecular absorption coefficient (ε), shorter λcut-off and easy introduction of chirality with hydrogen bonds into organic molecules. These advantages are useful to produce higher β values and second order nonlinear optical coefficients (dIJK) than nitro analogue, by controlling the molecular orientation in bulk crystals. In particular, CD substituted with chiral 1-amino-2-propanol is shown by x-ray crystallographic analyses to have a function to control molecular orientation one dimensionally in a mono-molecular plate of crystals with space group P1. By oriented gas model, very large d-values including off-diagonals were obtained. From the analysis of the Maker fringe pattern, the coefficient d11 of DAD ((-)-1-(4-dimethyl aminophenyl)-2-(2-hydroxypropylamino)cyclobutene-3,4-dione) was measured to be 200±40 pm/V.