KC₉H₅O₆(H₂O): A Promising UV Nonlinear-Optical Material with Large Birefringence Based on a π-Conjugated (C₉H₅O₆)⁻Group

Abstract

In order to meet the growing needs for the laser technology and optics industries, the goal is to find suitable fundamental building blocks with large nonlinear-optical (NLO) coefficients and birefringence for an excellent-performance NLO or birefringent system. Via preliminary investigations and calculations, it has been found that the planar π-conjugated group (C 9 H 5 O 6 ) − possesses large polarizability anisotropy (δ) and hyperpolarizability (β max ), comparable to well-known groups such as (B 3 O 6 ) 3− , (C 3 N 3 O 3 ) 3− , etc. Herein, we report a new alkali-metal 3,5-dicarboxybenzoate, KC 9 H 5 O 6 (H 2 O) (KH 2 BTC), which crystallized in the acentric space group Pna2 1 . Second-harmonicgeneration (SHG) measurements of KH 2 BTC under 1064 nm laser radiation show that the SHG response of KH 2 BTC is 1.2 times that of KDP with type I phase-matching behavior. Birefringence measurements show that KH 2 BTC owns a large birefringence of about 0.372 at 550 nm. The band gap of KH 2 BTC obtained by ultraviolet (UV) diffuse-reflectance spectroscopy is 3.91 eV, indicating that KH 2 BTC has potential applications as UV NLO or birefringent materials. Theoretical calculation further confirmed that the impressive optical properties of KH 2 BTC are derived from the large polarizability anisotropy of the (C 9 H 5 O 6 ) − anions.

A0.5H2C6N7O3·4H2O (A = Ca2+, Sr2+) iso-cyamelurates with ultra-large π-conjugated group and excellent nonlinear optical properties

“…Both I and II have rather wide band gaps (E g ) of 4.05 eV and 4.07 eV, respectively, corresponding to the cutoff edge of 306 nm and 304 nm. As expected, with the introduction of alkaline-earth metal cations, the obvious enhancement of E g is realized by comparison with the previously reported alkali 21,[46][47][48][49] Since I and II crystallize in the NCS space group of Fdd2, their NLO optical properties were investigated by SHG measurements using incident laser irradiation at a wavelength of 1064 nm. As shown in Fig.…”

“…The band gaps of I and II are comparable or larger than some other compounds featuring π-conjugated FBUs, such as K 2 Pb(H 2 C 3 N 3 O 3 ) 4 ·4H 2 O (3.9 eV), NH 4 Sb 2 (C 2 O 4 )F 5 (3.85 eV), Na 3 C 6 N 9 ·3H 2 O (4.16 eV), KC 9 H 5 O 6 (H 2 O) (3.91 eV), and [C(NH 2 ) 2 NHNO 2 ][C(NH 2 ) 3 ](NO 3 ) 2 (3.58 eV). 21,46–49…”

Intramolecular Hydrogen Bonds Enhance Structure Coplanarity, Resulting in Significant Birefringence in Bridged-Bipyridine Halides

“…At the maximum particle size (150–212 μm), the SHG intensities of 1 and 2 are about 0.32 and 0.56 times that of KDP with phase-matchable behavior, whereas 3 is perhaps phase matchable and shows SHG intensity, about 1.1 × KDP (Figure S6). Such SHG intensities of 1–3 are comparable or even greater than other organic–inorganic hybrid compounds, (2-AMP) 2 BiX 7 ·H 2 O (X = Cl/0.25 × KDP, Br/0.37 × KDP), KC 9 H 5 O 6 (H 2 O) (1.2 × KDP), and (C 3 H 7 N 6 ) 6 (H 2 PO 4 ) 4 (HPO 4 )·4H 2 O (0.1 × KDP) …”

NaCl·CH4N2O·H2O: An Organic–Inorganic Hybrid Ultraviolet Nonlinear Optical Crystal with Optimized Comprehensive Properties

“…The NLO-related properties of some reported NLO crystal materials containing organic π-conjugated groups are listed in Table . Compared to these materials, the band gap of NaCl·CH 4 N 2 O·H 2 O is wider than those of many organic–inorganic hybrid materials, such as BC 2 N 5 H 6 (OH) 2 ·H 2 O (4.79 eV), (C 5 H 6 ON)­(H 2 PO 4 ) (4.69 eV), Cs 3 Pb 2 (CH 3 COO) 2 I 5 (2.55 eV), RbNa­(HC 3 N 3 O 3 )·2H 2 O (5.1 eV), NaCs 3 (H 2 C 3 N 3 O 3 ) 4 ·3H 2 O (5.46 eV), and KC 9 H 5 O 6 (H 2 O) (3.91 eV) . The cutoff edge of NaCl·CH 4 N 2 O·H 2 O is comparable to that of urea (0.2 μm) .…”

“…Cs 3 Pb 2 (CH 3 COO) 2 I 5 (2.55 e V ) ,2 1 R b N a ( H C 3 N 3 O 3 ) • 2 H 2 O ( 5 . 1 e V ) ,2 4 NaCs 3 (H 2 C 3 N 3 O 3 ) 4 •3H 2 O (5.46 eV),44 and KC 9 H 5 O 6 (H 2 O) (3.91 eV) 45. The cutoff edge of NaCl•CH 4 N 2 O•H 2 O is comparable to that of urea (0.2 μm) 46.…”