2ND MOLECULAR HYPERPOLARIZABILITY OF 2,2'-DIAMINO-7,7'-DINITRO-9,9'-SPIROBIFLUORENE - AN EXPERIMENTAL-STUDY ON 3RD-ORDER NONLINEAR-OPTICAL PROPERTIES OF A SPIROCONJUGATED DIMER

Nonlinear optical properties of a fixed molecular dimer, 2,2'-diamino- 7,7'-dinitro-9,9'-spirobifluorene (ANSF), have been investigated in so lution by the degenerate four-wave mixing technique. It has been obser ved that the orientationally averaged second molecular hyperpolarizabi lity of ANSF in THF is enhanced ten times in comparison with its monom er unit, 2-amino-7-nitrofluorene. Since electronic coupling between mo nomer units in ANSF is negligible owing to symmetry, we attribute the large enhancement to the orientational effect of the two constituting dipoles with possible involvement of vibronic coupling and spiroconjug ation. (C) 1998 American Institute of Physics.