From H₁₂C₄N₂CdI₄ to H₁₁C₄N₂CdI₃: a highly polarizable CdNI₃ tetrahedron induced a sharp enhancement of second harmonic generation response and birefringence

Abstract

In this study, we identify a novel class of second-order nonlinear optical (NLO) crystal, non-π-conjugated piperazine (H10C4N2, PIP) metal halides, represented by two centimeter-sized, noncentrosymmetric organic-inorganic metal halides (OIMHs), namely...

Free Halogen Substitution of Chiral Hybrid Metal Halides for Activating the Linear and Nonlinear Chiroptical Properties

“…At various wavelengths, the SHG polar plots of DMA 4 [InCl 6 ]Br also show the same polarization direction (Figure S15). The dipolar profile is aptly modeled by a combination of sine and cosine functions, , with the polarization ratio, ρ = ( I max – I min )/( I max + I min ), calculated to be as high as ∼99.9% for DMA 4 [InCl 6 ]­Br, consistent with the values of DMA 4 [InCl 6 ]Cl (Figure S20). Such a remarkable polarization ratio is higher than those of most OIHMH materials. ,,– ,, The high anisotropy of the SHG response further suggests that the DMA 4 [InCl 6 ]Br crystals maintain excellent crystallinity after free halogen substitution.…”

“…On the contrary, the SHG intensity of M -DMA 4 [InCl 6 ]Br under right-handed circularly polarized laser is stronger than that under left-handed circularly polarized laser (Figure S21). The anisotropy factor g SHG‑CD , defined as g SHG‑CD = 2­( I L‑SHG – I R‑SHG )/( I L‑SHG + I R‑SHG ), is used to quantify the SHG-CD response, , where I L‑SHG and I R‑SHG denote the SHG intensities excited by left- and right-handed circularly polarized laser, respectively. DMA 4 [InCl 6 ]Br single crystals possess conspicuous circularly polarized sensitivity of SHG with a high g SHG‑CD value of 1.56, which is higher than that of DMA 4 [InCl 6 ]Cl owing to the introduction of free Br – and the increase of octahedral distortion (Figure S22).…”

“…Beard et al employed chiral OIHMHs as a spin filter to fabricate a spin-polarized LED with efficient circularly polarized electroluminescence. In 2018, our group demonstrated the observation of second harmonic generation circular dichroism (SHG-CD) responses from chiral OIHMHs, after which many new second-order NLO materials have been reported based on chiral perovskite structures, with the anisotropy factor ( g SHG‑CD ) reaching ∼0.80. – …”

From CdPb8(SeO3)4Br10 to Pb3(TeO3)Br4: the first tellurite bromide exhibiting an SHG response and mid-IR transparency

“…1–6 Second-order nonlinear optical materials require compounds to crystallize in non-centrosymmetric (NCS) space groups. 7–10 According to the ICSD database, the probability of obtaining a non-centrosymmetric structure is less than 20%. 11–13 So, the rational design of inorganic compounds with non-centrosymmetric symmetry remains a challenging but beneficial task for researchers in chemical and materials science.…”

Na10Zn(NO3)4(SO3S)4: a nonlinear optical crystal combining inorganic π-conjugated and non-π-conjugated heteroanion groups

“…28 Recently, researchers have proposed design strategies to improve the birefringence and NLO properties of non-π-conjugated systems. 29 One of these strategies involves the partial substitution of anions in tetrahedral units to form heteroanion groups like BO x F 4− x ( x = 1, 2, 3), 30 PO x F 4− x ( x = 1, 2, 3), 31 SO x F 4− x ( x = 1, 2, 3), 32 and SiO x F 6− x ( x = 1, 2, 3, 4, 5). 33 Indeed, these non-π-conjugated heteroanion groups result in large birefringence and NLO coefficients of compounds like NH 4 B 4 O 6 F, 34 (NH 4 ) 2 PO 3 F, 31,35 NaNH 4 PO 3 F·H 2 O, 35,36 C(NH 2 ) 3 SO 3 F 37 and so on.…”