New Internal-Charge-Transfer Second-Order Nonlinear Optical Chromophores Based on the Donor Ferrocenylpyrazole Moiety

Abstract

A series of new N-arylated ferrocenepyrazole structures, carrying different donor or acceptor substituents in the para position of the aryl ring has been synthesized by the Chan-Lam cross coupling reaction. The nonplanar geometric molecular structure of some of these chromophores together with their crystal packing was determined by X-ray diffraction and the HOMO and LUMO energy levels were evaluated by electrochemical and optical measurements and by DFT theoretical calculations. By the investigation of solvent effects and TD-DFT calculations the intense electronic absorption band at around 270-310 nm was confirmed to be an internal-charge-transfer (ICT) band, showing a significant red shift by increasing the electron withdrawing properties of the substituent on the para position of the aryl ring. TD-DFT calculations and EFISH measurements of the quadratic hyperpolarizability have shown that also the second order NLO response of these new ICT chromophores can be tuned by changing the nature of the substituent. Both theoretical µβ, β and experimental EFISH µβ 1907 and β 1907 values are significant, with a quite satisfactory correlation of the general trend of theoretical µβ and EFISH µβ 1907 values. The highest value of EFISH µβ 1907 (410 x 10 -48 esu) was measured for the chromophore carrying the strong electron withdrawing NO 2 group. KSK thanks to DST for Inspire fellowship (IF-110138). KSK and NP gratefully acknowledge SIF DST-VIT-FIST, VIT University, Vellore for providing NMR, Mass and IR data. MP thanks, Prof. for their extremely useful suggestions and comments.

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 1 H NMR spectrum of the N-arylated ferrocenyl pyrazole shows the following types of signals: ferrocenyl moiety shows different signals, and (i) the unsubstituted cyclopentadienyl ring of ferrocene exhibits a sharp singlet around δ = 4.00 ppm; (ii) the monosubstituted cyclopentadienyl ring shows doublets in the region δ = 4.57-4.78 ppm; (iii) the proton signal of the pyrazole ring is attributed at δ = 6.89, 6.62 ppm, respectively; (iv) the singlet peaks at δ = 1.27, 3.78 ppm are associated with the substituted CH 3 and OCH 3 protons; and (v) the phenyl ring protons appear in the region 6.85-7.75 ppm. [25] The 13 C NMR spectrum of aromatic carbons gives resonance in the range of 100-150 ppm, [44] and the Ar-CH 3 and Ar-OCH 3 carbons for compounds 1 and 2 were observed at δ 31.3 ppm and δ 55.5 ppm, and the characteristic C-N coupling peak at about δ 137.0 (1) and 132.5 (2) ppm was assigned for phenyl carbon attached to pyrazole moiety. The values of the 19 F chemical shift for (-CF 3 ) may be used to give a tentative indication of the environment around fluorine atoms.…”

“…The overlap pictograms (Figures 2 and S11) of the aromatic rings exhibit non-covalent interactions (hydrogen bonding and πÁÁÁπ stacking). [25] F I G U R E 1 The molecular structure of the N-arylated ferrocenyl pyrazoles 1 and 2 with 50% probability Strong NLO chromophores generally have large dipole moments, which leads to extensive dipole-dipole interactions between chromophores. [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.…”

“…[24] Our group has reported ferrocene containing 5-methyl-substituted pyrazole derivatives for dual-mode detection of H 2 O 2 and the NLO properties of N-arylated ferrocenyl pyrazole. [25] Herein, we build our previous work to develop the electron-withdrawing effect of trifluoromethyl (CF 3 ) substituent in N-arylated ferrocene pyrazole. Trifluoromethyl group exhibits unique properties such as thermal stability, excellent solubility in organic solvents, low moisture uptake, low dielectric constant and high optical transparency.…”

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

“…Later, many Schiff bases were reported for their AIE behaviour, such as phenylbenzoxazole, pyridine and a variety of imines in tetrahydrofuran–water and water. Once such materials are identified as having NLO response, they can be further utilized for the development of photonic devices such as those for optical data storage, optical communication and optical limiting …”

“…In one of our earlier reports, we studied the NLO property of ferrocenyl Schiff base highlighting the significance of the C═N linkage . Also we further explored NLO properties of ferrocene‐based D‐π‐A pyrazoles and quinoxaline . The current work focuses on the synthesis and characterization of the molecular structure, electronic properties and redox behaviour of compounds, both experimentally and theoretically.…”