Ferrocene‐appended donor–π–acceptor Schiff base: Structural, nonlinear optical, aggregation‐induced emission and density functional theory studies

Abstract

New ferrocenyl Schiff bases [Fc─C(H)═N─C 6 H 3 (OH)(R)] (R = H (1), NO 2 (2)) have been synthesized and characterized using various techniques. Compound 2 was further confirmed using single-crystal X-ray diffraction analysis.Solvatochromism studies of 2 showed redshift from nonpolar to polar solvents. In addition, results of fluorescence studies indicated excellent aggregationinduced emission properties. The quasi-reversible redox wave in electrochemical studies of the Schiff bases evidenced the electron transfer ability of ferrocene to the Schiff base (─C═N─) conjugation group. The second-order nonlinear optical (NLO) properties of 1 and 2 were investigated using the Kurtz-Perry powder technique and 2 showed an effect 1.46 times greater than that of urea reference. Although 2 crystallized in the P2 1 /c centrosymmetric space group, NLO property was observed, due to non-covalent interactions (C─H⋅⋅⋅π). The band gaps were calculated using the diffuse reflectance spectroscopic method and 2 exhibited a low band gap of 2.9 eV which is due to the more electronwithdrawing nature of the nitro group. Quantum chemical calculations were performed on the synthesized compounds using the density functional theory (DFT) and time-dependent DFT approach. The theoretical studies showed that the band gap for the Schiff bases was 3.8 eV (1) and 3.2 eV (2) and they can be considered as candidates for use in optical applications. KEYWORDS aggregation-induced emission (AIE), DFT/TD-DFT, electrochemical studies, ferrocenyl Schiff bases, nonlinear optics | INTRODUCTIONResearch on ferrocene-containing compounds has drawn immense attention due to their wide-ranging applications in the fields of catalysis, [1] sensors, [2] luminescent systems, [3] nonlinear optics [4a] and molecular electronic devices [5] due to their well-established redox switching abilities. [6] Since ferrocene displays a good electrochemical response because of its strong π-donating ability and good reversibility in one-electron oxidation at a desirable

A comparison between observed and DFT calculations on structure of 5-(4-chlorophenyl)-2-amino-1,3,4-thiadiazole

“…This was occurred from the molecular orbitals of the auxochrome (NH 2 ) of exocyclic nitrogen lone pairs and the conjugated π-bond of azomethine (-C=N-N=C-) of 1,3,4-thiadiazole moiety. With the increasing the solvent polarity from non-polar to polar, n→π* transition get slightly shifted towards longer wavelength, which was probably due to the solvatochromic effect (Tables 6 and 7) 37 . Compound 3 displayed a positive absorption solvatochromism, which signifies that the absorption was redshifted with cumulative solvent polarity.…”

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

“…This AIE effect is much larger than that previously observed for ferrocenyl Schiff bases, for which 4-9-foldq uantum yield enhancements were reported upon the addition of asuitable amount of water. [41] These results prompted us to study more deeplyt he aggregation phenomenono ft he b-ketoimines andr elated BF 2 complexes in the presenceo fC H 3 CN/H 2 Om ixtures.H igh-resolution transmission electron microscopy (HRTEM) was used to study L4 and the related BF4;s amples were obtainedb yd rop-casting their solutions, either in pure CH 3 CN or in aC H 3 CN/H 2 O (1:9, v/v) mixture, ontoc opperg rids. The HRTEM images obtained from the CH 3 CN/H 2 Om ixtures in Figure 7s how the presence of spherical aggregates with as ize of 4-6 nm.…”

Aggregation induced emission (AIE)‐active N‐arylated ferrocenyl pyrazole‐based push–pull chromophores: Structural, photophysical, theoretical and effect of substitution on second‐order non‐linear optical properties

“…The β values for 1 and 2 are surprising, considering the crystallization in the centrosymmetric space group for 1 (P 1) and for 2 (P2 1 /n), which was unexpected high non-linear susceptibility, and values are due to the presence of non-covalent (C-HÁÁÁO, C-HÁÁÁF and C-HÁÁÁπ) interactions of π-electrons within the molecule. [50,69,72] The results indicate that the substituent group has a great effect on the NLO response and has more significant difference when comparing the high β values (38.6 × 10 −30 and 116.8 × 10 −30 e.s.u.). In D-π-A-π-D structure, methoxy (OCH 3 ) acts as stronger electron donor group with higher first hyperpolarizabilities due to mesomeric effect (+M), when compared with methyl (CH 3 ) substitution, which have lower NLO response as expected from the inductive effect.…”

“…[49] The C-HÁÁÁπ interaction between the two phenyl rings in the ranges of 3.338 (1) and 2.948 Å (2) is shown in Figure S11, which enables NLO activity, though the molecule crystallizes in the centrosymmetric space group. [50] The packing diagram of N-arylated ferrocenyl pyrazole shows that fluorine generates a different type of packing patterns C-HÁÁÁF through trifluoromethyl atoms ( Figure 2). The fluorine atoms participate in the hydrogen bonds with aromatic ring hydrogen (2.747 Å, 164.25 for compound 1 and 2.805 Å, 146.91 for compound 2), and there is a significant contribution of fluorine in crystal packing that is in a good agreement with previously reported values.…”

“…[28] The HOMO energy levels of 1 and 2 were calculated to be −5.13 and −5.20 eV, respectively, according to the following equation: HOMO = −(4.4 + E ox ) eV. [50] The E g was estimated to be 3.36 (1) and 3.42 (2) eV by the onset wavelength of UV-Vis absorption, respectively, and the calculated LUMO energy levels of 1 and 2 were listed in Table 1.…”