NLO-active Y-shaped ferrocene conjugated imidazole chromophores as precursors for SHG polymeric films

Contemporary Developments in Ferrocene Chemistry: Physical, Chemical, Biological and Industrial Aspects

Ferrocenyl-based compounds have many applications in diverse scientific disciplines, including in polymer chemistry as redox dynamic polymers and dendrimers, in materials science as bioreceptors, and in pharmacology, biochemistry, electrochemistry, and nonlinear optics. Considering the horizon of ferrocene chemistry, we attempted to condense the neoteric advancements in the synthesis and applications of ferrocene derivatives reported in the literature from 2016 to date. This paper presents data on the progression of the synthesis of diverse classes of organic compounds having ferrocene scaffolds and recent developments in applications of ferrocene-based organometallic compounds, with a special focus on their biological, medicinal, bio-sensing, chemosensing, asymmetric catalysis, material, and industrial applications.

Luminescent 1,10-Phenanthroline β-Diketonate Europium Complexes with Large Second-Order Nonlinear Optical Properties

Substitution of the diglyme ligand of [Eu(hfa)₃(diglyme)] (where hfa is hexafluoroacetylacetonate) with a simple 1,10-phenanthroline leads to a six-fold increase of the product μβ_EFISH, as measured by the Electric-Field-Induced Second Harmonic generation (EFISH) technique. Similarly, [Eu(tta)₃(1,10-phenanthroline)] (where Htta is 2-thenoyltrifluoroacetone) is characterized by a large second-order NLO response. Both 1,10-phenanthroline europium complexes have great potential as multifunctional materials for photonics.

Ferrocene appended 1,8-naphthalimide chromophores: Synthesis, theoretical, the effect of phenyl substitution on aggregation-induced enhanced emission and second-order nonlinear optical studies

A new ferrocene appended linear donor-π-acceptor (D-π-A) type 1,8-naphthalimide chromophores [FcPhNap-n-butyl (1) and Fc(Ph)₂Nap-n-butyl (2)] have been synthesized and characterized using various analytical and spectroscopic techniques. The chromophores 1 and 2 show the one-electron transfer process, which was examined through cyclic voltammetric (CV) method. The solvatochromic studies show red shift by increasing the solvent polarity from non-polar to polar for both the chromophores 1 and 2, due to the better stabilization of the more polarized excited state than the ground state in the polar solvent. The fluorescence studies show low fluorescence emission, which was enhanced by aggregation in THF/water mixture when the water ratio is increased upto 60%, due to the restricted intramolecular rotation (RIR) process in the aggregated state. Also, the quantum yield increases 3.4 (1) and 6.8 (2) times in the aggregation induced enhanced emission (AIEE) state than THF solution for both the chromophores [THF/AIEE = 0.05/0.17 for 1 and 0.03/0.22 for 2]. The second-order non-linear optical properties of the chromophores 1 and 2 were studied using Kurtz and Perry powder technique, chromophore 2 shows 1.2 times higher SHG efficiency than 1, owing to the presence of additional phenyl group in 2, which further supports the effective charge transfer process from donor to acceptor. Furthermore, optical and non-linear optical properties of chromophores 1 and 2 were analyzed by DFT/TD-DFT calculations using different functionals (B3LYP, long-range corrected CAM-B3LYP and LC-BLYP) with 6-31+G** level of theory. The B3LYP functional shows higher hyperpolarizability values [β₀ = 109.2 × 10^-30 esu (1), 299.7 × 10^-30 esu (2)], due to the overestimation of the dipole moment, polarizability and hyperpolarizabilities between the donor-π-acceptor systems in B3LYP-hybrid functional, which leads to incorrect long-range charge transfer.

Novel Ferrocene-Appended β-Ketoimines and Related BF2 Derivatives with Significant Aggregation-Induced Emission and Second-Order Nonlinear Optical Properties

A series of new β-ketoimines containing a ferrocene moiety and their BF₂ complexes have been synthesized and structurally characterized. The solvatochromism of the β-ketoimines was studied, putting in evidence a redshift with increasing solvent polarity. This positive solvatochromism can be attributed to a more polarized excited state compared with the ground state, due to intramolecular charge transfer (ICT) transitions. The β-ketoimines exhibited weak emission, attributable to the excited-state intramolecular proton transfer (ESIPT) phenomenon. This ESIPT effect is suppressed upon restriction of the keto-enamine tautomerism, induced upon addition of BF₃ ⋅OEt₂ , which afforded the related BF₂ complexes, characterized by an enhancement of the fluorescence through the ICT effect. Both the β-ketoimines and BF₂ complexes exhibited significant aggregation-induced emission behavior in mixtures of CH₃ CN/H₂ O, due to restriction of intramolecular rotation in the aggregated state. The frontier molecular orbital levels, ground- and excited-state dipole moments (μ_g and μ_e ), and the origin of electronic absorption spectra were studied by time-dependent DFT calculations. The second-order nonlinear optical (NLO) properties were determined by the electric-field-induced second-harmonic generation technique. The μβ₁₉₀₇ values of the β-ketoimines increased upon the formation of the related BF₂ complexes, mainly due to an enhancement of the ground-state dipole moment. The results presented here reveal that some of these novel compounds are excellent multifunctional candidates for NLO and luminescence applications.

Ferrocene-appended boronated ester: effect of cyanovinylene group on the nonlinear optical properties and colorimetric detection of fluoride ion

A centrosymmetric ferrocenyl boronated ester shows second-order NLO effect, selective and sensitive detection of fluoride ion.

Cyclometalated Ir(III) Complexes with Curcuminoid Ligands as Active Second-Order NLO Chromophores and Building Blocks for SHG Polymeric Films

The second-order nonlinear optical (NLO) properties of iridium(III) complexes having two cyclometalated 2-phenylpyridines and curcumin or tetrahydrocurcumin as ancillary ligand have been investigated both in solution and as guest in a polymeric organic matrix. In solution, these complexes are characterized by a significant second-order NLO response, as determined by the Electric Field Induced Second Harmonic (EFISH) technique, like the related complex with acetylacetonate. Whereas the low second-harmonic generation response of a composite film of [Ir(2-phenylpyridine)2(acetylacetonate)] in polymethyl methacrylate was not stable and fell down to zero upon turning off the electric field. A good and stable response was obtained with a film based on the iridium(III) complex bearing two cyclometalated 2-phenylpyridines and curcumin.

Palladium(ii) complexes of tetradentate donor–acceptor Schiff base ligands: synthesis and spectral, structural, thermal and NLO properties

Structural and NLO behavior of push–pull palladium(ii) complexes of metallocenyl-containing asymmetric Schiff base ligands.