Organic Phenolic Configurationally Locked Polyene Single Crystals for Electro‐optic and Terahertz Wave Applications

Abstract

We investigate a configurationally locked polyene (CLP) crystal 2‐(3‐(4‐hydroxystyryl)‐5,5‐dimethylcyclohex‐2‐enylidene)malononitrile (OH1) containing a phenolic electron donor, which also acts as a hydrogen bond donor. The OH1 crystals with orthorhombic space group Pna21 (point group mm2) exhibit large second‐order nonlinear optical figures of merit, high thermal stability and very favorable crystal growth characteristics. Higher solubility in methanol and a larger temperature difference between the melting temperature and the decomposition temperature of OH1 compared to analogous CLP crystals, are of advantage for solution and melt crystal growth, respectively. Acentric bulk OH1 crystals of large sizes with side lengths of up to 1 cm with excellent optical quality have been successfully grown from methanol solution. The microscopic and macroscopic nonlinearities of the OH1 crystals are investigated theoretically and experimentally. The OH1 crystals exhibit a large macroscopic nonlinearity with four times larger powder second harmonic generation efficiency than that of analogous CLP crystals containing dimethylamino electron donor. A very high potential of OH1 crystals for broadband THz wave emitters in the full frequency range of 0.1–3 THz by optical rectification of 160 fs pulses has been demonstrated.

Molecular Origins of the High-Performance Nonlinear Optical Susceptibility in a Phenolic Polyene Chromophore: Electron Density Distributions, Hydrogen Bonding, and ab Initio Calculations

“…Furthermore, a slightly asymmetric charge distribution was calculated between the two cyano groups where the charge transfer seems to tend more toward the −C(2)N (14) group. This can be rationalized by the observation that the N(14) atom acts as a hydrogen-bond acceptor of the primary intermolecular interaction, OH···N, the existence of which has been reported previously; 25 this hydrogen bond will lead to an increase in electronegativity of the −C(2)N(14) group relative to that of the other cyano group. Table 2 also presents net charges for various functional groups of OH1 using two other atomic partitioning methods commonly employed in charge-density studies: the Stockholder and QTAIM methods.…”

“…The previous report on the crystal structure of OH1 from room-temperature X-ray diffraction [25][26][27]56 suggested that five intermolecular interactions were present; tentative hydrogen-bond separations were given, although X-rays cannot locate hydrogen accurately. In contrast, the neutron-derived crystal structure of OH1, reported herein, gives an accurate measure of hydrogen positions and so is well suited to hydrogen-bonding characterization.…”

Hydrogen-bond-directed-linking solving transparence-efficiency tradeoff in nonlinear optical molecule

“…Yang et al investigated that hydrogen bonds between the sulfonic oxygen atoms and double-bond hydrogen atoms play a role in crystal packing and chromophores orientation [37]. Especially, Kwon et al proposed [38] a configurationally locked polyene (CLP) crystal 2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (OH1) containing a phenolic electron donor, which also acts as a hydrogen bond donor, which exhibited highly efficient second-harmonic generation at 1907 nm fundamental wavelength. Nagalakshmi et al [39] calculated that the first hyperpolarizability of single crystals of hydroxyethylammonium l-tartrate monohydrate [HEALT] stabilized by a set of intermolecular hydrogen bonds is found to be 4.238 × 10 −30 esu, which is 14.2 times that of urea.…”

Pd‐Promoted Homocoupling Reactions of Unsaturated Silanes in Aqueous Micelles

“…Accordingly, as a first exploration in this direction, we report herein our study on the micellar version of a Pd-promoted homocoupling process of vinyl-and polyenylsilanes that we had previously shown to be an efficient methodology to synthesize extended stereodefined all-trans polyenes up to eight conjugated double bonds long, by doubling in one step the conjugated system of the starting unsaturated silanes. [9] The significance of polyenes in studies dealing with organic electronics is manifold: conjugated polyenes have been investigated as molecular conductors [10] and switches, [11] optical conductors, [12] optical diodes, [13] and nonlinear optical (NLO) materials. [14] Moreover, due to their well-defined chemical structure and possibility of selective functionalization, they represent valuable model systems for validation of predictions based on theoretical calculations and for developing new concepts in organic electronics.…”