A Photochromic Zinc–Viologen Framework with a High-Contrast Nonlinear Optical Switchable Behavior

Abstract

As an important branch of nonlinear optical (NLO) switches, second-harmonic-generation (SHG) switches undergoing reversible SHG-on and SHG-off states upon external stimuli exposure have been the focus of intense scientific research due to their potential applications in photoelectric technologies. The high-contrast switching of SHG, a key issue for the potential applications of SHG optical switches, has been a challenge but is undoubtedly very interesting. Incorporating stimuli-responsive molecules into the SHG-active materials is an efficient approach to construct high-contrast SHG switches. In this paper, by using the ligand 1-(4-cyanobenzyl)-4,4′-bipyridinium (CBbpy) as a photosensitive group, a noncentrosymmetric photochromic zinc–viologen framework, {[(CBbpy)­Zn3(TBC)­(HTBC)­(OH)]·NO3}n (1; H3BTC = 1,3,5-benzenetricarboylic acid), has been obtained. It shows an SHG intensity of 1.1 × KH2PO4 (KDP) due to the synergistic effect of the coplanar and parallel arrangement of NO3 – anions, the asymmetric disposition of electron densities, and the large permanent dipole moment, as confirmed by Bader charge and dipole moment calculations. More importantly, an outstanding SHG switching contrast was found to be at least 23 times larger than that of the coloration sample under a 1064 nm laser beam, originating from the large difference in the dipole moment and the self-absorption effect before and after coloration. Such excellent SHG switching is reversible and can be cycled several times, indicating that 1 is a good candidate as a new solid-state SHG-switching material. This work should prompt researchers to explore novel high-performance SHG switches based on devisable stimuli-responsive groups.

Two-Dimensional Organic–Inorganic Hybrid Materials with Dielectric Switching and Photoluminescence Properties

“…Organic–inorganic hybrid materials − have attracted considerable attention because of their flexible structure and remarkable properties, such as photovoltaic, ferroelectric − and. piezoelectric, and nonlinear optical (NLO) properties. − Among them, layered two-dimensional (2D) organic–inorganic halide perovskites − (as an emerging semiconducting materials, they possess a strong quantum confinement effect to achieve high PLQYs and, moreover, photochromism can also be adjusted by halogen) have widespread applications in solar cells, , light emitting diodes (LEDs), − and photodetectors. − …”

Single‐Component Photochromic Smart Semiconductor with Photoswitchable Fast Bidirectional Electron Transfer

“…Photochromic materials, a crucial subclass of intelligent species, have two switchable stable or metastable states with contrasting colors and physical properties. [1][2][3][4][5] Including photochromic functional motifs [6,7] into semiconductors confers intelligent behavior and color-related applications on semiconductors. For instance, Hecht, Samorì, and colleagues created optically switchable transistors by incorporating photochromic molecules into semiconducting polymer matrices; [8,9] we developed and implemented the ideas of color-indicating smart circuit protection [10,11] and color-and-electricity-indicating dualmode radiation detection and imaging [12] based on singlecomponent viologen-based photochromic semiconductors.…”

Thermally-driven unusual dual SHG switching with wide SHG-active steps triggered by inverse symmetry breaking

“…10,11 Past studies have shown that the majority of switching SHG compounds exhibit single-step transformation between NCS (SHG-on) and CS structure (SHG-off ) by an external stimulus. [12][13][14][15][16][17] For example, single-component molecular crystal 2-(hydroxymethyl)-2-nitro-1,3-propanediol exhibits a high contrast SHG-on/off ratio at around the phase transition temperature of 340 K, 18 the pressure-controlled SHG-on/off of CdTeMoO 6 , 19 thermally-induced inverse SHG off/on of K x (NH 4 ) 2−x PO 3 F (x = 0-0.3), 20 and both photo-and heatinduced SHG-switching behaviors of β-[(MQ)ZnCl 3 ] (MQ + = N-methyl-4,4′-bipyridinium). 21 Other examples are representative NCS (SHG-high) to NCS (SHG-low) materials, such as (R/S)-3-quinuclidinol 22 and (BA) 2 (EA) 2 Pb 3 I 10 .…”