Nondipolar Structures With Threefold Symmetry For Nonlinear Optics

Abstract

Abstract The second‐order polarizabilities β(— 2ω; ω, ω) of six nondipolar NLO chromophores—1,3,5‐tris(isopropyl‐amino)‐2,4,6‐trinitrobenzene ( 1 ), 1,3,5‐tris(isopropylamino)‐2,4,6‐tris(trifluoro‐methylsulfonyl)benzene ( 2 ), tris(dimethyl‐imoniomethyl)methide diperchlorate ( 3 ), 2,4,6‐tris[4‐( N,N ‐diethylamino)phenyl‐ethynyl]‐1,3,5‐triazine ( 4 ), 2,4,6‐tris[4‐( N,N ‐diethylamino)phenyl]‐1,3,5‐triazine ( 5 ), and tris(2‐dimethylaminoethenyl)‐methinium perchlorate ( 6 )—were studied by polarized hyper‐Rayleigh scattering (HRS). The NLO activity of these two‐dimensional NLO chromophores is attributed to three‐level contributions to the β values, for which different optimization strategies are investigated. Exceptionally large second‐order polarizabilities were observed for the conjugationally elongated structures: the β value of triazine 4 is 15 times larger than that of the one‐dimensional two‐level chromophore 4‐nitroaniline. Results obtained with the polarized HRS experiment are discussed with respect to local field corrections, calibration, and systematic sources of error.