Second-order nonlinear optics in coordination chemistry: An open door towards multi-functional materials and molecular switches

Solid-State Nonlinear Optical Properties of Mononuclear Copper(II) Complexes with Chiral Tridentate and Tetradentate Schiff Base Ligands

“…The derivative [Ni(4,4′-diNEt 2 -sal-(1 R ,2 R )-dpen)] with 1,2-diphenylethylenediamine (dpen) was then synthesized by changing the chemical nature of the chiral diamine, and studied for its solid-state NLO response. The powder SHG efficiency @1.907 µm of this nickel(II) complex, which crystallizes in the monoclinic P 2 1 space group, is 13 times that of urea [23,49], close to the upper limit [10] in this class of complexes [17]. As a reference, 3-methyl-4-nitropyridine-1-oxide (POM), a molecular material that entered the market also thanks to its transparency and ability to be grown as large crystals, has a large SHG efficiency equal to 13 times that of urea [50].…”

“…Among other organometallic [11,12,13,14,15] and coordination compounds [14,15,16,17,18], salen-type [19] metal complexes have been actively studied for their NLO properties, mostly for the last two decades [17,18,20,21,22,23]. The best functionalization of these derivatives has been achieved by inserting donor (D) groups on the salicylaldehyde (sal) moieties and acceptor (A) groups on the diamine bridge, such as substituted 1,2-diaminobenzene (phen) and diaminomaleonitrile (damn).…”

“…Such push-pull bis(salicylaldiminato) metal complexes with charge asymmetry generated by electron releasing and withdrawing groups on the ligand skeleton have shown promising results for their SHG efficiency in solution through electric field induced second harmonic (EFISH) generation and hyper rayleigh scattering (HRS) measurements [24,25,26,27,28,29,30,31,32,33]. This class of compounds has also been the subject of extensive theoretical studies through the years in order to elucidate their electronic and optical features [17,26,32,34,35,36,37]. As an alternative to the above-mentioned push-pull structure, we focused our attention on salen-type metal complexes in which the A–D asymmetry is achieved by push-pull unsymmetrical substitution on the sal moieties, firstly on copper(II) derivatives [38], and very recently also on nickel(II) compounds [39].…”

Structural Variation and Switchable Nonlinear Optical Behavior of Metal–Organic Frameworks

“…[ 3 ] Observing the impact of structural changes in a certain material on the corresponding NLO responses is an valid method to reveal this relationship. [ 4 ] A number of micro/nano materials have been reported so far to display the contrast in NLO behavior via commuting between two or more structures, yet only the change of a single NLO behavior is involved. [ 5 ] For the development of multifunctional integrated photonics, the establishment of theoretical models based on highly‐designable materials to synchronously study the relationships between structural variations and multiple NLO properties is fundamentally and technologically significant, whereas still suffers from lacking suitable NLO materials.…”

Arylthienyl-vinyl-benzothiazoles as Efficient Second Harmonic Generators (SHG) for Nonlinear Optics

“…Organic molecules comprising strong electron donor and acceptor groups connected by a πconjugated system (often designated as donor-π-acceptor or "push-pull" chromophores) are of fundamental importance in materials chemistry due to their numerous applications in modern technology, such as nonlinear optical (NLO) devices, poled polymers, photovoltaic cells, organic light-emitting diodes (OLEDs), semiconductor materials, and optical data storage devices [1][2][3][4]. Several push-pull molecules containing benzothiazole as an (auxiliary) electron-withdrawing group have already been reported, and typically exhibit favorable fluorescence, electrochemical, solvatochromic, photochromic, and NLO properties [5][6][7].…”