Second molecular hyperpolarizability of 2,2′-diamino-7,7′-dinitro-9,9 ′- spirobifluorene: An experimental study on third-order nonlinear optical properties of a spiroconjugated dimer

Abstract

Nonlinear optical properties of a fixed molecular dimer, 2,2′-diamino-7,7′-dinitro9,9 ′-spirobifluorene (ANSF), have been investigated in solution by the degenerate four-wave mixing technique. It has been observed that the orientationally averaged second molecular hyperpolarizability of ANSF in THF is enhanced ten times in comparison with its monomer unit, 2-amino-7-nitrofluorene. Since electronic coupling between monomer 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 spiroconjugation. © 1998 American Institute of Physics.