Helquat Dyes: Helicene-like Push–Pull Systems with Large Second-Order Nonlinear Optical Responses

Abstract

Helquat dyes combine a cationic hemicyanine with a helicene-like motif to form a new blueprint for chiral systems with large and tunable nonlinear optical (NLO) properties. We report a series of such species with characterization, including determination of static first hyperpolarizabilities β0 via hyper-Rayleigh scattering and Stark spectroscopy. The measured β0 values are similar to or substantially larger than that of the commercial chromophore E-4'-(dimethylamino)-N-methyl-4-stilbazolium. Density functional theory (DFT) and time-dependent DFT calculations on two of the new cations are used to probe their molecular electronic structures and optical properties. Related molecules are expected to show bulk second-order NLO effects in even nonpolar media, overcoming a key challenge in developing useful materials.

Helicenes Grafted with 1,1,4,4‐Tetracyanobutadiene Moieties: π‐Helical Push–Pull Systems with Strong Electronic Circular Dichroism and Two‐Photon Absorption

“…The nonlinear optical (NLO) activity of helicenes has long been known,e specially second-order NLO effects and second harmonic generation (SHG). [19] More recently,t he two-photon absorptiono fh elicenes has also been examined,t ogether with the related two-photon circular dichroism. [8] These studies on organic helicene derivativesh ave highlighted the effects of charge transfer (either internally to the helical backbone or external to it) and of p-conjugation extension.…”

Dutch Resolution of a configurationally stable [5]helquat

“…[16][17][18][19][20][21][22][23][24][25][26][27][28] Representative examples are heterohelicenium systems studied by Lacour group 20 or helical dications called helquats developed by our group. 23 These and similar cationic systems promise attractive range of properties and applications [29][30][31][32][33][34][35][36][37][38] that may be complementary to non-ionic helicenes. For example, they can strongly interact with their environment due to their positively charged helical skeleton.…”

Novel poly(aryl ether ketone) with electro-optic chromophore side chains for light modulators

“…This resulted in better film-forming ability, higher electro-optics coefficients and better long-term stability. Quantum chemical simulations of the second order polymers have been reported in the past two decades, it is very difficult to find organic second order nonlinear optical materials that have both large electro optic coefficients and long-term stability [13][14][15][16][17][18]. Due to the large EO coefficients of about 42-78 pm/V (all the EO parameters are given at wavelength 1.3 µm) at low chromophore loading density (10 wt%), chromophore CLDs have been widely studied, but their thermal decomposition temperature is very low (~180 °C) [53].…”