Discovery of NLO Semiorganic (C₅H₆ON)⁺(H₂PO₄)⁻: Dipole Moment Modulation and Superior Synergy in Solar-Blind UV Region

Abstract

We herein report a novel semiorganic NLO material, (C 5 H 6 ON) + (H 2 PO 4 ) − , 4HPP, showing promising excellent properties in the important solar-blind UV region where LAP and its deuterated form DLAP are the only commercialized semiorganic materials. For the first time, the 4-hydroxypyridine (4HP + , (C 5 H 6 ON) + ) cation is identified as NLO active and how to eliminate the dipole−dipole interaction to avoid the unwanted center-symmetry-trap caused by the polar-induced susceptibility is well demonstrated. Remarkably, 4HPP exhibits competitive and even better properties compared with LAP that include better thermal stability (decomposition at 166 vs 112 °C of LAP); wider transparency range (0.26−1.50 μm); very strong SHG response (3 × KDP); a suitable large birefringence (Δn cal = 0.25 vs 0.075 of LAP); and a high laser-induced damage threshold (2.2 × KDP). Firstprinciples calculations show that the π-conjugated organic (4HP) + cation governs the optical anisotropy, whereas the synergy of the organic and inorganic moieties dominates the SHG process. Our discovery points out a new path for the rational design of high performance semiorganic materials that require an acentric structure.

[o‐C5H4NHOH]2[I7O18(OH)]⋅3 H2O: An Organic–Inorganic Hybrid SHG Material Featuring an [I7O18(OH)] Branched Polyiodate Chain

“…The organic–inorganic hybrid SHG materials can combine the excellent properties of inorganic groups and the structural diversities of organic groups [25] such as (C 5 H 6 ON) + (H 2 PO 4 ) − [26] and [C(NH 2 ) 3 ] 6 (PO 4 ) 2 ⋅3 H 2 O [27] reported recently. Up to now, there has been only one organic–inorganic hybrid SHG polyiodate, namely, (C 6 H 16 N 2 O 2 )(IO 3 )(I 2 O 5 OH), been reported [25] .…”

Two molybdenyl carbonates with different dimensional structures exhibiting huge differences in band gaps

“…[1][2][3][4][5][6][7][8] Highquality NLO materials should satisfy the following standards: large SHG response, wide transmission band, appropriate birefringence, good physical and chemical stability, and facile growth of crystals. [9][10][11][12][13] Most importantly, it is essential that an NLO crystal should be noncentrosymmetric (NCS) without a center of symmetry. However, it is always a huge challenge to design novel NCS crystalline materials because both the functional units and the arrangement of these units could affect the macroscopic symmetry of the compound.…”

Avoiding the Center‐Symmetry Trap: Programmed Assembly of Dipolar Precursors into Porous, Crystalline Molecular Thin Films

“…Solids with noncentrosymmetric (NC) structure (i.e., those lacking spatial inversion symmetry) exhibit a variety of interesting properties, e.g., piezoelectricity and nonlinear optical (NLO) effects including second‐harmonic generation (SHG). [ 1 ] Furthermore, the corresponding absence of inversion symmetry is a prerequisite for integrating static electric fields into a material.…”

“…Generally, for dipolar asymmetric building blocks, electrostatic interactions favor the formation of dimers with antiparallel dipoles, which then aggregate into larger units. This quenching of macroscopic electrostatic fields, occasionally referred to as center‐symmetry trap, [ 1 ] is a general process in self‐assembly of dipolar building blocks [ 11 ] prohibiting the formation of NC structures. In selected cases, sophisticated H‐bonding schemes have been employed to achieve head‐to‐tail arrangements with aligned dipoles and interesting electro‐optical effects.…”