Nonlinear optical properties of curcumin: solvatochromism-based approach and computational study

Nonlinear Optical Properties and All Optical Switching of Curcumin Derivatives

In this work OR1(E1,6E) -1,7-bis (4-propyloxy phenyl) hepta-1,6-diene-3,5 dione compound is synthesized. The compound has been characterized via computational technique by studying the molecule's electronic structures through calculating its HOMO and LUMO energies, and its band gap energy (EHOMO-ELUMO). The nonlinear refractive index (NLRI) of the solution of OR1 compound in DMF solvent is determined using diffraction patterns (DPs) which resulted when a continuous wave laser beam of wavelength 473 nm traversed the compound solution in a glass cell of 1 mm thickness. By counting the number of rings under maximum beam input power, the NLRI of value 10- 6 cm2/W resulted. The NLRI is calculated once more via the Z-scan technique and a value of 0.25 × 10- 7 cm2/W is obtained. The vertical convection current in the OR1 compound solution appears to be responsible for the asymmetries noticed in the DPs. The temporal variation of each DP is noticed together with the evolution of DPs against beam input power. DPs are numerically simulated based on the Fresnel-Kirchhoff integral with good accord compared to the experimental findings. Dynamic and static all-optical switching in the OR1 compound using two laser beams (473 and 532 nm) is tested successfully.

Curcumin Analogue Spectral, Nonlinear Optical Properties and All-optical Switching Using Visible, Low Power Cw Laser Beams

In this study, we conducted the synthesis and diagnosis of compound denoted as 1A3, specifically, (2E,4E,9E,11E)-7-chloro-2,12-diphenyltrideca-2,4,9,11-tetraene-6,8-dione. The photoluminescent and UV-vis spectral properties of this compound are investigated. The compound is dissolved in both chloroform and DMF for analysis purposes. Compound 1A3's nonlinear optical (NLO) characteristics when dissolved in DMF, are extensively studied through a series of experiments including diffraction patterns (DPs) and Z-scan. The optical limiting (OL) property of the 1A3 compound is tested and a threshold value of 12.4 mW at the wavelength 473 nm is obtained. Additionally, we explored its potential for all-optical switching utilizing two low-power visible laser beams. Notably, we achieved a significant nonlinear refractive index (NLRI) reaching up to 5.921 x 10-11 m2/W. To analyze the obtained diffraction patterns, we employed the Fresnel-Kirchhoff integral equation and conducted meticulous simulations. The numerical outcomes showed satisfactory agreement with the experimental observations.

Theoretical Perspective toward Designing of 5-Methylbenzo [1,2-b:3,4-b':6,5-b″] trithiophene-Based Nonlinear Optical Compounds with Extended Acceptors

A series of benzotrithiophene-based compounds (DCTM1-DCTM6) having D1-π1-D2-π2-A configuration were designed using a reference molecule (DCTMR) via incorporating pyrrole rings (n = 1-5) as the π-spacer (π2). Quantum chemical calculations were performed to determine the impact of the pyrrole ring on the nonlinear optical (NLO) behavior of the above-mentioned chromophores. The optoelectronic properties of the compounds were determined at the MW1PW91/6-311G(d,p) functional. Among all of the derivatives, DCTM5 exhibited the least highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) band gap (Eg) 0.968 eV with a high softness of 0.562 eV-1, and hence possessed the highest polarizability. Interestingly, transition density matrix (TDM) findings demonstrated that DCTM5 with an effective diagonal charge transmission proportion at the acceptor group supports the frontier molecular orbital (FMO) results. Additionally, the exciton binding energy values for DCTM1-DCTM6 were found to be less than that for DCTMR and thus, the effective charge transfer was examined in the derivatives. All of the derivatives exhibited effective NLO outcomes with the highest magnitude of linear polarizability ⟨α⟩, and first (βtot) and second (γtot) hyperpolarizabilities relative to the parent compound. Nevertheless, the highest βtot and γtot were obtained for DTCM1 and DTCM6, 7.0440 × 10-27 and 22.260 × 10-34 esu, respectively. Hence, through this structural tailoring with a pyrrole spacer, effective NLO materials can be obtained for optoelectronic applications.

Extraction of Natural Pigment Curcumin from Curcuma Longa: Spectral, DFT, Third-order Nonlinear Optical and Optical Limiting Study

Herein, we report the extraction of natural pigment curcumin from curcuma longa and their linear and third-order nonlinear optical (NLO) characteristics. The characterization techniques viz., UV-Visible absorption, FT-IR, Micro Raman and Gas Chromatography Mass Spectrum (GC-MS) are used to study the spectral characteristics of curcumin. Third-order NLO features of curcumin are studied using Z‒scan technique with a semiconductor diode laser working at 405 nm wavelength. The natural pigment exhibits negative nonlinear index of refraction resulting from self-defocusing and positive coefficient of absorption is the consequence of reverse saturable absorption (RSA). The order of nonlinear index of refraction (n2) and nonlinear coefficient of absorption (β) is measured to be 10-7 cm2/W and 10-2 cm/W, respectively. Third-order NLO susceptibility (χ(3)) and second-order hyperpolarizability (γ) of curcumin is measured to be 2.73 × 10‒7 esu and 1.67 × 10‒31 esu, respectively. A low optical limiting (OL) threshold of 0.71 mW is observed in the extracted pigment. The experimental results are supplemented by quantum mechanical calculations of the NLO parameters. The overall result finding is that curcumin extracted from curcuma longa has the potential to be novel optical candidates for photonics and optoelectronics applications.

Role of donors in triggering second order non-linear optical properties of non-fullerene FCO-2FR1 based derivatives: A theoretical perspective

The organic compounds are known as an emerging class in the field of nonlinear optical (NLO) materials. In this paper, D-π-A configured oxygen containing organic chromophores (FD2-FD6) were designed by incorporating various donors in the chemical structure of FCO-2FR1. This work is also inspired by the feasibility of FCO-2FR1 as an efficient solar cell. Theoretical approach involving DFT functional i.e., B3LYP/6-311G(d,p) was utilized to achieve useful information regarding their electronic, structural, chemical and photonic properties. The structural modifications revealed significant electronic contribution in designing HOMOs and LUMOs for the derivatives with lowered energy gaps. The lowest HOMO-LUMO band gap obtained was 1.223 eV for FD2 compound in comparison to the reference molecule (FCO-2FR1) i.e., 2.053 eV. Moreover, the DFT findings revealed that the end-capped substituents play a key role in enhancing the NLO response of these push-pull chromophores. The UV-Vis spectra of tailored molecules revealed larger λ _max values than the reference compound. Furthermore, strong intramolecular interactions showed the highest stabilization energy (28.40 kcal mol^-1) for FD2 in the natural bond orbitals (NBOs) transitions, combined with the least binding energy (-0.432 eV). Successfully, the NLO results were favorable for the same chromophore (FD2) which showed the highest value for dipole moment (μ _tot = 20.049 D) and first hyper-polarizability (β _tot = 11.22 × 10^-27 esu). Similarly, the largest value for linear polarizability ⟨α⟩ was obtained as 2.936 × 10^-22 esu for FD3 compound. Overall, the designed compounds were calculated with greater NLO values as compared to FCO-2FR1. The current study may provoke the researchers towards designing of highly efficient NLO materials via using the suitable organic linking species.

In silico screening of ethyl 4-[(E)-(2-hydroxy-4-methoxyphenyl)methyleneamino]benzoate and some of its derivatives for their NLO activities using DFT

The nonlinear optical (NLO) properties of ethyl 4-[(E)-(2-hydroxy-4-methoxyphenyl)methyleneamino]benzoate (EMAB) and some of its derivatives are investigated herein using the density functional theory (DFT) and time-dependent (TD)-DFT methods. The density functionals B3LYP, CAM-B3LYP, M06-2X and ωB97XD, and basis sets 6-31 + G**, 6-311 + + G** and Def2-TZVPP have been used. From the results, EMAB and its substituted derivatives studied are promising candidates for NLO materials. In all cases, the static first and second hyperpolarizabilities (31.7-86.5 × 10^-30 and 84.4-273 × 10^-36 electrostatic units (esu), respectively) and the frequency-dependent NLO properties are found to be significantly larger (about 43-103 and 28-76 times greater) than those of the NLO prototypical molecule, para-nitroaniline. Furthermore, the maximum absorption wavelengths of the molecules fall within the UV region of the electromagnetic spectrum. Relative to EMAB, the derivatives have shown improved transparency-nonlinearity trade-offs. Natural bond orbital (NBO) and density of states (DOS) analyses herein revealed effective charge transfer within the molecules studied, especially those with stronger electron donors than that in EMAB (methoxy group). Among the molecules studied, the derivative obtained by substituting EMAB's methoxy group with the pyrrolyl group was found to exhibit the best NLO properties. Conclusively, the NLO activities of EMAB can be significantly improved through the substitution of its methoxy group with stronger electron donors.

Study of nonlinear optical responses of phytochemicals of Clitoria ternatea by quantum mechanical approach and investigation of their anti-Alzheimer activity with in silico approach

Clitoria ternatea is a flowering plant with promising medicinal plants with a wide variety of active phytochemicals. The present study aimed at the computational investigation of the nonlinear optical (NLO) responses of the active phytochemicals of the Clitoria ternatea. The computational investigation of the NLO features was done by using the density functional theory (DFT) by B3LYP/6-311G + + (d, p) basis set. The structural parameters, mulliken charge distribution, and molecular electrostatic potential (MEP) surface clearly show the intramolecular charge transfer within Clitorin. The NLO properties were identified by computing the polarizability parameters. As the plant has high medicinal characteristics, the inhibiting properties of its phytochemicals were also investigated to combat Alzheimer disease (AD). The systematic in silico study identifies Clitorin as the most active and inhibiting phytochemicals of the plant. The results obtained from molecular dynamics (MD) simulation tell the stability of the complex and make it a fair selection as a drug-like molecule against AD. The cardio-toxicity analysis done for the Clitorin molecule verifies that it is harmless for the heart.

Supplementary information

The online version contains supplementary material available at 10.1007/s11224-022-01981-5.

Enriching NLO efficacy via designing non-fullerene molecules with the modification of acceptor moieties into ICIF2F: an emerging theoretical approach

Non-fullerene (NF)-based compounds have attracted much attention as compared to fullerene-based materials because of their promising optoelectronic properties, lower synthetic cost and greater stability. Usually, the end-capped groups have a promising impact in magnifying the nonlinear optical (NLO) characteristics in the non-fullerene molecules. Based on this, a series of new NLO active non-fullerene molecules (NFAD2-NFAD6) have been established. The non-fullerene molecules (NFAD2-NFAD6) were designed by end-capped modification in acceptor moieties of the reference (NFAR1), while donor and π-bridge moieties were kept the same in the entire series. Quantum chemistry-based calculations at the M06/6-311G(d,p) level were done to determine the NLO characteristics and for other supportive analyses. The acceptor and donor moieties were utilized at the opposite terminals of NFAD2-NFAD6, which proved to be an effective approach in tuning the FMO band gap. Overall the results of natural bond orbital (NBO), density of state (DOS) and transition density matrices (TDMs) analyses supported the NLO properties of the designed compounds. Among all the studied compounds, NFAD4 was proven to be the most suitable candidate due to its promising NLO properties, well supported by a lower bandgap of 1.519 eV and a maximum absorption wavelength of 999.550 nm. Therefore, NFAD4 was reported with greater amplitude of dipole polarizability (10.429 e.s.u), average polarizability (2.953 × 10^-22 e.s.u), first hyperpolarizability (13.16 × 10^-27 e.s.u.) and second hyperpolarizability (2.150 × 10^-31 e.s.u.) than other derivatives and NFAR1. Subsequently, the present study depicted the significance of utilizing different non-fullerene (NF)-based acceptor moieties to achieve the promising NLO material. This computational study may lead towards new plausible pathways for researchers to design potent NLO substances for impending hi-tech applications.

Hybrid Synthetic and Computational Study of an Optimized, Solvent-Free Approach to Curcuminoids

A green and optimized protocol has been developed for the preparation of symmetric 1,7-bis(aryl)-1,6-heptadiene-3,5-diones and asymmetric 2-aryl-6-arylidenecyclohexanones with modified substrate scope and good functional group tolerance. Syntheses proceed smoothly under solvent-free conditions, providing moderate to excellent product yields with a minimal workup procedure. Control experiments, spectroscopic, and computational studies support a mechanism involving the boron-assisted in situ generation of imine intermediates. Crystal structures of three curcuminoids and isolated mechanistic intermediates are reported. The data provide insight for the further development of solvent-free protocols toward diverse curcumin derivatives in the fields of pharmaceutical and synthetic chemistries.

External electric field modulated second-order nonlinear optical response and visible transparency in hexalithiobenzene

External electric fields (EEFs) offer a unique opportunity to tune certain activity of molecules by orienting the alignment of the electric field along the specific axis. The second-order NLO response of hexalithiobenzene (C₆Li₆) is very poor due to its first mean hyperpolarizability of 0.5 a.u. Therefore, we have analyzed the effect of EEFs on the structural, electronic properties, and NLO response of C₆Li₆ using a density functional approach. We notice that the structure of the C₆Li₆ molecule remains planar, with the slight change in C-C and C-Li bond lengths, but their stability is increased under the effect of EEFs. By applying EEFs, the conductivity or reactivity of C₆Li₆ is increased as their HOMO-LUMO energy gap is decreased. Furthermore, C₆Li₆ attains a finite dipole moment in the presence of EEF, which increases linearly as the EEF increases. More interestingly, the first static hyperpolarizability of C₆Li₆ is significantly enhanced, becoming as high as 3.4 × 10⁴ a.u. for EEF = 50 × 10^-4 a.u. This suggests the EEF as an effective way to enhance the second-order NLO responses, leading to the design of potential NLO materials. Nevertheless, the visible transparency of C₆Li₆ with and without EEF may suggest its possible applications in optical devices.

The nonlinear optical properties of two dihydropyridones derived from curcumin

Two dihydropyridone compounds are synthesized from curcumin using microwave radiation. Both compounds were identified by their melting points and ¹HNMR spectra. The nonlinear properties viz., nonlinear absorption coefficients and nonlinear refractive index of both compounds were calculated at wavelength 473 nm using the diffraction ring patterns and Z-scan techniques separately. The diffraction ring patterns evolved from circular symmetric to asymmetric due to convection current in the vertical direction. As a result of using Gaussian laser beam, the Fraunhofer approximation of the Fresnel-Kirchhoff diffraction, have led to successful simulation of the diffraction ring patterns with good quantitative and excellent qualitative agreements compared with experimental results. Optical limiting property has been tested in both compounds.

Novel blue-green emitting NLOphoric triphenylamine-imidazole based donor-π-acceptor compound: Solvatochromism, DFT, TD-DFT and non-linear optical studies

Novel Donor (D)-π-Acceptor (A) NLOphoric triphenylamine-imidazole based dye 9 was designed, synthesized, and confirmed by Mass, ¹³C NMR, and ¹H NMR analysis. Photophysical properties of 9 were studied in solvents of different polarities and compared with analogues compounds 7 and 8. Phenonthroline acceptor based dye 9 shows highly bathochromic shifted absorption and emission compared to dyes 7 and 8. Positive solvatochromism was noticed in 7, 8, and 9 which was supported by the linear (i.e. Lippert-Mataga and Mac-Rae polarity functions) and multi-linear (i.e. Kamlet-Taft and Catalan parameters) analysis. Moreover, solvent polarizability (d_SP) and solvent dipolarity (C_SdP) are the major factors responsible for red shift in absorption as well as in emission spectra. Charge transfer descriptors as well as the polarity graphs are in good relation with Generalized Mulliken-Hush (GMH) parameters. NLO properties of 7, 8, and 9 were studied by using solvatochromic and computational methods. The static first hyperpolarizability (β₀) and relevant microscopic parameters (μ,α₀,α,β,γ) were determined using DFT with B3LYP, BHHLYP, and CAM-B3LYP functionals. Third-order NLO properties of nitrogen containing phenanthroline based compound 9 were observed to be several times higher than those of the compounds 7 and 8, justify the design approach.

Ultra-High to Ultra-Low Drug-Loaded Micelles: Probing Host-Guest Interactions by Fluorescence Spectroscopy

Polymer micelles are an attractive means to solubilize water insoluble compounds such as drugs. Drug loading, formulations stability and control over drug release are crucial factors for drug-loaded polymer micelles. The interactions between the polymeric host and the guest molecules are considered critical to control these factors but typically barely understood. Here, we compare two isomeric polymer micelles, one of which enables ultra-high curcumin loading exceeding 50 wt.%, while the other allows a drug loading of only 25 wt.%. In the low capacity micelles, steady-state fluorescence revealed a very unusual feature of curcumin fluorescence, a high energy emission at 510 nm. Time-resolved fluorescence upconversion showed that the fluorescence life time of the corresponding species is too short in the high-capacity micelles, preventing an observable emission in steady-state. Therefore, contrary to common perception, stronger interactions between host and guest can be detrimental to the drug loading in polymer micelles.

Chlorine (Cl) - Substituted Carbazole Based A-π-D-π-a Push-Pull Chromophores as Aggregation Enhanced Emission (AEE) Active Viscosity Sensors: Synthesis, DFT and NLO Approach

Three new carbazole functionalized A-π-D-π-A extended chromophores 4a, 4b and 4c comprising of different chemical functional groups on C=C bond with the assistance of chlorovinylene group in π-conjugation are synthesized and investigated spectroscopically. We have investigated the effect of different electron acceptors - carboxycyanomethylene, dicyanomethylene and 2-(benzothiazol-2-yl) cyanomethylene, the effect of the insertion of chlorine in π-conjugation on photophysical properties and the effect of double acceptors. The chromophores 4a, 4b and 4c exhibited positive solvatochromism with large Stokes shifts and bright orange to red solid-state fluorescence. Amongst all the three compounds 4c exhibited maximum emission wavelength at 615 nm in DMSO. They presented characteristic twisted intramolecular charge transfer (TICT) emission. Observations exhibited that 4c containing long hexyl group in donor unit and 2-(benzothiazol-2-yl) cyanomethylene as an acceptor group formed an aggregate in the mixture of solvents and exhibited better aggregation enhanced emission (AEE) compared to the other two derivatives. Amongst the three styryls, 4c showed the highest emission intensity 299 a.u. at 90% water:DMF fraction (f_w). Chromophores 4a-4c also exhibited good fluorescence response towards viscosity. Among the three fluorescent molecular rotors (FMR), 4c exhibited excellent viscosity sensitivity with x value = 0.687. The Non-linear (NLO) characters are estimated with the help of solvatochromic and computational methods using the functionals, B3LYP and CAM-B3LYP. The dyes showed large "linear polarizability (α_CT)", "first order hyperpolarizability" (β) and "second order hyperpolarizability" (γ) values which show that synthesized styryls can be used as a "NLO" material. The α_CT, β and γ for 4c are found to be the maximum amongst the all three dyes which can be ascribed to the smaller band gap apparent from experimental as well as DFT method.