Engineering hydrogen bonding to align molecular dipoles in organic solids for efficient second harmonic generation

Abstract

We switch the molecule from SHG inert to SHG active by controlling the degree of hydrogen bonding through protonation.

Second-order nonlinear optical organic crystals based on a “click” compound

“…Due to these dipole-dipole interactions, molecules in crystal structures tend to self-assemble in anti-parallel arrangements, leading to a zero macroscopic polarizability. 47 The overall inherent dipole moment in the unit cell of aand b-phases are calculated to be non-zero (Fig. 3c and d), thanks to the noncentrosymmetric arrangements of BPTA molecules.…”

“…45 Furthermore, the internal forces between these special units increase the intermolecular interactions and could induce the preferred molecular packing. 46,47 The click reaction is a facile and efficient method to synthesise 1,2,3-triazole analogous compounds, which includes n-p molecular units such as -NQNand might have promising NLO properties. A few triazole based organic compounds have been indeed reported to be NLO active.…”

Self-assembled organic nonlinear optical crystals based on pyridine derived fluorenone

“…Due to the strong dipoledipole interactions, these molecules tend to self-assembly in anti-parallel arrangements, which would result in zero macroscopic polarizability. [16][17][18] Thus, the design of organic NLO materials with large optical nonlinearities at both the molecular and macroscopic levels remains a significant challenge.…”

α- and β-(C4H5N2O)(IO3)·HIO3: Two SHG Materials Based on Organic–Inorganic Hybrid Iodates

“…Recently, π-conjugated planar organic moieties have been successfully developed as potential NLO-active groups due to their large polarizability anisotropy, ultrafast response time, and infinite design probabilities. – When the organic moieties act as anions, for instance, the (H x C 3 N 3 Q 3 ) (3– x )– (Q = O, S; x = 0, 1, and 2) groups have been harnessed to build many SHG crystals such as Ca 3 (C 3 N 3 O 3 ) 2 (SHG: >2 × β-BaB 2 O 4 ), KLi­(HC 3 N 3 O 3 )·2H 2 O (5.3 × KDP), RE 5 (C 3 N 3 O 3 ) (OH) 12 (RE = Y, Yb, and Lu) (2.5–4.2 × KDP), and Cs 3 Cl­(HC 3 N 3 S 3 ) (11.4 × KDP). – Theoretical calculations revealed that the organic moieties dominate the SHG effects of these materials. – The organic groups can also function as cations, for example, the [C­(NH 2 ) 3 ] + group has been widely used as a SHG building group as in [C­(NH 2 ) 3 ] 6 (PO 4 ) 2 ·3H 2 O (3.8 × KDP), C­(NH 2 ) 3 SO 3 F (5 × KDP), and [C­(NH 2 ) 3 ] 2 [B 3 O 3 F 4 (OH)] (1.4 × KDP). ,– It is noticed that the pyridine and pyrimidine derivative groups featuring nitrogen-containing heteroaromatic rings could be protonated and used to build organic–inorganic hybrid SHG crystals such as [ o -C 5 H 4 NHOH] 2 [I 7 O 18 (OH)]·3H 2 O (8.5 × KDP), (C 5 H 6 ON) + (H 2 PO 4 ) − (3 × KDP), and (C 4 H 6 N 3 ) + (H 2 PO 3 ) − (2 × KDP). ,, …”