Strong Electron Acceptor Group Research Articles

Comparative analyses of Nonlinear Optical (NLO) properties, structural characterization and density functional theory of chloro-trifluoromethyl moiety chalcone derivatives for optical limiting application

This study focuses on the impact of substitutional positions on the nonlinear optical (NLO) and photophysical properties of four novel chalcone derivatives (I–IV). The grown crystals were characterized using FT-IR, NMR and single crystal X-ray diffraction (SCXRD) techniques, and the intermolecular interactions were studied by examining the unique packing motifs. The linear and 3rd-order NLO properties were experimentally determined using UV–Vis spectrometer and Z-scan setup with 637 nm continuous wave excitation, respectively. Compounds I–IV were studied theoretically using density functional theory (DFT) to support the experimental results. B3LYP functional was used to optimize the geometries, and the molecular properties of the compounds were determined via molecular electrostatic potential (MEP), natural population analysis (NPA), and localized orbital locator-π (LOL-π) analyze. The photophysical properties were analyzed using time-dependent DFT (TDDFT) using both CAM-B3LYP and B3LYP functionals to investigate the impact of the long-range correction. Inter-fragment charge transfer (IFCT) analysis and hole-electron analysis were employed to examine the linear optical properties and charge transfer mechanism. The NLO properties such as dipole moment (μ), polarizability (α), first and second hyperpolarizabilities (β and γ) were examined with the numerically differentiate analytic method using both functionals. Z-scan NLO data shows that the nonlinear refraction (NLR) coefficient of I–IV is significantly influenced by intermolecular interactions, specifically aggregation phenomena. Compound IV exhibits an exceptional nonlinear absorption (NLA) response and superior optical limiting properties compared to others attributed to its para-substituted strong electron-acceptor group (CF3) which results in highest transition dipole moment, lowest excitation energy, and well-defined charge transfer processes within its molecule. As a result, this suggests that it could be a potential candidate for NLO applications.

An experimental and DFT investigations of fused ring anthracenyl chalcones with effective modification in acceptor moiety: Nonlinear optical and optical limiting response

AbstractThe significance of the anthracene moiety on nonlinear optical (NLO) characteristics is thoroughly examined. The presence of strong electron donor and acceptor groups, large and prolonged conjugation transfer axis, amplifies the push–pull action and increases NLO responses. The values of χ3 obtained for AC derivatives are considerably larger (10−3 esu), indicating that they accurately reflect NLO reactions. According to the optical limiting (OL) investigation, AC has a strong limiting behavior with action beginning at 1.6 KW/cm2. The relationship between transmittance and intensity has demonstrated their potential use in OL applications. Nonlinear optical studies show that all conjugated anthracene chalcones are potential materials for OL devices.

Evolving a novel red-emitting two-photon dye with optically tunable amino group for monitoring the degree of hypoxia during liver fibrosis

Two-photon imaging has attracted increasing attention owing to its deep tissue imaging capabilities. Therefore, many fluorophores have been developed to satisfy its requirements. However, long-wavelength emission fluorophores with an optically tunable group are rarely developed. In this study, two long-wavelength emission fluorophores with an optically tunable amino group were successfully developed by introducing strong electron acceptor and large conjugated group to the TPQL dye. TPCO2 displayed a bright red emission (λem = 638 nm, Φ = 0.15) together with high two-photon action cross section and good water solubility, which enabled higher signal-to-background ratios and deep tissue imaging. The proof-of-concept probe (TPCONO2) was successfully applied to the high signal-to-background ratio imaging of nitroreductase in liver fibrosis, further realizing diagnosis of the degree of hypoxia during liver fibrosis.

The Influences of Sulfoxide Electron Traps in Transparent Polyimides with Low Retardation, Yellow Index, and CTE

AbstractDue to the development of dynamic flexible organic light‐emitting diode displays, colorless polyimides (CPI) as the supporting or protecting optical films, are facing significant challenges due to the requirements of optical, mechanical, thermal, and chemical properties. Typical CPIs are derived from TFDB (2,2‐bis(trifluoro‐methyl)‐4,4′‐diaminobiphenyl)/6FDA (4,4′‐(hexafluoroisopropylidene)diphthalic anhydride), which still need to be improved in both dimensional stability and optical performance. In this communication, a strong electron acceptor group, the sulfoxide bond, is first introduced into the TFDB block of CPI chains. Based on this introduction, the distribution of the electron cloud in the polymer chain is reconstructed under the strongly pulling electron effect, and the spatial conformation of the polymer chain is also affected by the rigid and twisted sulfoxide group. The influences on CPI's optical properties, especially the refractive index and the retardation, are studied and discussed in detail by experimental results and theoretical calculations. It is shown that the CPI with the sulfoxide group exhibits higher optical transparency, lower yellow index, phase retardation and coefficient of thermal expansion, which is an ideal material for CPI optical films.

VIRTUAL SCREENING OF HETEROCYCLIC COMPOUNDS AGAINST ANGIOTENSIN-CONVERTING ENZYME FOR POTENTIAL ANTIHYPERTENSIVE INHIBITORS

Objective: The objective of this study was to investigate the antihypertensive activity of heterocyclic compounds against angiotensin-converting enzyme (ACE) through molecular docking studies.
 Methods: The X-ray crystal three-dimensional (3D) structure of human ACE complexed with lisinopril (PDB ID: 1O86) was retrieved from protein databank. The two-dimensional structures of 10 selected heterocyclic compounds were drawn in ACD-Chemsketch and converted into 3D structures. The 3D structures of compounds were virtually screened in the binding pockets of ACE using FlexX docking program. Further, the chemical entities revealing the molecular electronic structures of the best docked compound (Compound-4) were explored through density functional theory studies.
 Results: The Compound-4 showed the highest docking score of −26.6290 kJ/mol with ACE. The Hbond and non-bonded interactions are favored by phenylalanine, leucine, and arginine. The energy gap of 1.60 eV between highest occupied molecular orbital and lowest unoccupied molecular orbitals explained the presence of strong electron-acceptor group. Furthermore, the molecular electrostatic potential studies clearly envisaged the requirement of electropositive and electronegative groups are crucial for the ACE inhibitor activities.
 Conclusion: The identification of good ACE inhibitors requires the understanding of the current ACE inhibitors. Thus, the docking interactions of Compound-4 and its molecular electronic structure significantly imply its potential as antihypertensive agent. However, further clinical studies are required to ascertain its potential toxic effects.

Spectroscopic analysis and charge transfer interaction studies of 4-benzyloxy-2-nitroaniline insecticide: A density functional theoretical approach

A widespread exploration on the intra-molecular charge transfer interaction through an efficient π-conjugated path from a strong electron-donor group (amino) to a strong electron-acceptor group (nitro) has been carried out using FTIR, FT-Raman, UV–Vis, fluorescence and NMR spectra on insecticide compound 4-benzyloxy-2-nitroaniline. Density functional theory method is used to determine optimized molecular geometry, harmonic vibrational wavenumbers and intensities using 6-311G(d,p) basis set by means of Gaussian 09W program suit. A comprehensive investigation on the sp2 to sp3 hybridization and non-planarity property has been performed. Natural bond orbital analysis is used to study the existence of C–H⋯O, N–H⋯O and C–H⋯π proper and improper hydrogen bonds. The HOMO and LUMO analysis reveals the possibility of charge transfer within the molecule. A complete assignment of the experimental absorption peaks in the ultraviolet region has also been performed. Isotropic chemical shifts of 13C, 1H, 15N and 18O NMR and nuclear spin–spin coupling constants have been computed using the gauge-invariant atomic orbital method. The biological activity of substituent amino and nitro groups are evident from the hydrogen bonds through which the target amino acids are linked to the drug as evidenced from molecular docking.

Synthesis and optoelectronic characterization of some triphenylamine-based compounds containing strong acceptor substituents

Three novel triphenylamine-based compounds containing strong electron acceptor groups have been synthesized and their comparative photophysical properties are presented. These compounds were obtained by a two-step method: (i) triphenylamine compounds with one, two and three phenylacetylene arms were synthesized by Sonogashira reaction between iodine-substituted triphenylamines and phenylacetylene, followed by (ii) post-modification of these electron-rich alkynes by addition of the strong electron acceptor, tetracyanoethylene. Characterization of all oligomers was made by FTIR, 1H-NMR, UV–vis and fluorescence spectroscopy. A batochromic shifting of the UV and photoluminescence maxima was observed with the increase of the acceptor group number. The electrochemical behavior was studied by cyclic voltammetry. The cyclic voltammograms have evidenced that triphenylamine-phenylacetylene compounds undergo only oxidation processes while compounds modified with tetracyanoethylene show both oxidation and reduction peaks associated with donor and acceptor groups, respectively. The donor–acceptor compounds coordinate metal ions (i.e., Hg2+ and Sn2+) by cyano groups resulting in the decreasing of charge transfer band intensity, and they can be used as chemosensors.

Molecular structure, Mulliken charge, frontier molecular orbital and first hyperpolarizability analysis on 2-nitroaniline and 4-methoxy-2-nitroaniline using density functional theory

In the present study, we made an attempt to calculate the energy gap, molecular dipole moment and first hyperpolarizability of 2-nitroaniline (2NA) and 4-methoxy-2-nitroaniline (4M2N) with a basis set 6-31G (d, p) function has been employed at density functional theory (DFT) methods. Geometry optimizations was carried out with DFT-B3LYP/6-31G (d, p), the results have revealed that intramolecular hydrogen bonding present in both the molecular system. We analyzed the energy gap, molecular dipole moment and hyperpolarizability changes due to substitution effect of the methoxy group in 2NA molecule. It is confirmed that strong electron acceptor and donor groups in a material yield higher NLO response.

Electron transfer dynamics and excited state branching in a charge-transfer platinum(II) donor-bridge-acceptor assembly.

A linear asymmetric Pt(ii) trans-acetylide donor-bridge-acceptor triad designed for efficient charge separation, NAP[triple bond, length as m-dash]Pt(PBu3)2[triple bond, length as m-dash]Ph-CH2-PTZ (), containing strong electron acceptor and donor groups, 4-ethynyl-N-octyl-1,8-naphthalimide (NAP) and phenothiazine (PTZ) respectively, has been synthesised and its photoinduced charge transfer processes characterised in detail. Excitation with 400 nm, ∼50 fs laser pulse initially populates a charge transfer manifold stemming from electron transfer from the Pt-acetylide centre to the NAP acceptor and triggers a cascade of charge and energy transfer events. A combination of ultrafast time-resolved infrared (TRIR) and transient absorption (TA) spectroscopies, supported by UV-Vis/IR spectroelectrochemistry, emission spectroscopy and DFT calculations reveals a self-consistent photophysical picture of the excited state evolution from femto- to milliseconds. The characteristic features of the NAP-anion and PTZ-cation are clearly observed in both the TRIR and TA spectra, confirming the occurrence of electron transfer and allowing the rate constants of individual ET-steps to be obtained. Intriguingly, has three separate ultrafast electron transfer pathways from a non-thermalised charge transfer manifold directly observed by TRIR on timescales ranging from 0.2 to 14 ps: charge recombination to form either the intraligand triplet (3)NAP with 57% yield, or the ground state, and forward electron transfer to form the full charge-separated state (3)CSS ((3)[PTZ(+)-NAP(-)]) with 10% yield as determined by target analysis. The (3)CSS decays by charge-recombination to the ground state with ∼1 ns lifetime. The lowest excited state is (3)NAP, which possesses a long lifetime of 190 μs and efficiently sensitises singlet oxygen. Overall, molecular donor-bridge-acceptor triad demonstrates excited state branching over 3 different pathways, including formation of a long-distant (18 Å) full charge-separated excited state from a directly observed vibrationally hot precursor state.

Modulation of the Second-Order Nonlinear Optical Properties of the Two-Dimensional Pincer Ru(II) Complexes: Substituent Effect and Proton Abstraction Switch

The static second-order nonlinear optical (NLO) properties on a series of the two-dimensional (2D) pincer Ru(II) complexes with the substituted Tpy and H(2)SCS tridentate ligands (Tpy = 2,2':6',2″-terpyridyl and H(2)SCS = 2,6-bis(benzylaminothiocarbonyl)phenyl) have been investigated by density functional theory (DFT). Introducing different donor/acceptor substituents to two ligands has an influence on the static first hyperpolarizabilities (β(tot)) of the 2D systems. Compared to the reference system 1 [Ru(H(2)SCS)(Tpy)](+), introducing the branches with strong electron acceptor group (p-NO(2)-phenylethynyl) to the Tpy ligand or the branches with strong electron donor group (p-NH(2)-phenylethynyl) to the H(2)SCS ligand can effectively improve the β(tot) values. Time-dependent DFT (TDDFT) calculations indicate that the enhanced β(tot) values of the substituted systems are dominated by the intraligand charge transfer (ILCT), metal-to-ligand charge transfer (MLCT) and ligand-to-metal charge transfer (LMCT) transitions. Furthermore, the proton abstraction plays an important role in tuning the second-order NLO response. Particularly, for system 5 bearing the branches with NO(2) groups on H(2)SCS ligand, there is a dramatic enhancement in the β(tot) values for its deprotonated forms. The β(tot) values of the monodeprotonated system 5-H and the dideprotonated system 5-2H (58.712 × 10(-30) and 761.803 × 10(-30) esu) are about 7.58 times and 36.4 times larger than their diprotonated system 5, respectively. The second-order NLO responses based on substituent effect and proton abstraction switch are two-dimensional in characteristic with the large off-diagonal tensor values.

Diels–Alder reactions of nitrobenzofurans: a simple dibenzofuran Synthesis. Theoretical studies using DFT methods

2- and 3-nitrobenzofurans are studied in polar thermal Diels–Alder reactions with normal electron demand using several structurally different dienes. A very strong electron-acceptor group, such as the nitro group, pushes the dienophilic character of these heterocyclic compounds. Since this substituent is easily extruded under thermal conditions, this reaction sequence becomes a simple method for the preparation of families of organic compounds with heteroatom rings. Part of this work is specifically concerned with theoretical studies using DFT methods. The global and local electrophilicity and nucleophilicity indices were calculated for the dienophiles and dienes used in this study. When 2-nitrobenzofuran and 3-nitrobenzofuran were reacted with isoprene, 1-trimethylsilyloxy-1,3-butadiene and Danishesfky’s diene, under different thermal reaction conditions they showed their dienophilic character taking part in normal-demand polar DA cycloaddition reactions.

ChemInform Abstract: Arylmaleic Anhydrides via Heck Arylation of Fumaric Acid.

AbstractThe coupling is facilitated by the presence of donor substituents at the aryl fragment and does not occur with strong electron acceptor groups.

The synthesis, electrochemical and theoretical nonlinear optical properties of push–pull chromophores for photorefractive composites

Four chromophores, of different dipole moment and polarizable anisotropy and which comprised conjugation bridges of both benzene and polyene with strong electron-donor and electron-acceptor groups, were characterized using 1H NMR, FT-IR, UV–vis, and electrochemical analyses. The electric dipole moment ( μ), polarizability ( α) and the first hyperpolarizability ( β) values of the chromophores were examined using computational methods. The contribution of orientational birefringence to total birefringence was estimated from the calculated molecular parameters of the chromophores; these parameters are important factors for predicting photorefractive efficiency.

Efficient π-electron conjugated push–pull nonlinear optical chromophore 1-(4-methoxyphenyl)-3-(3,4-dimethoxyphenyl)-2-propen-1-one: A vibrational spectral study

As part of the efforts for the design new organic nonlinear optical (NLO) materials with high efficiency for present day technological requirements, a comprehensive investigation on the intramolecular charge transfer (ICT) of an efficient π-conjugated potential push–pull NLO chromophore, 1-(4-methoxyphenyl)-3-(3,4-dimethoxyphenyl)-2-propen-1-one to a strong electron acceptor group through the π-conjugated bridge has been carried out from their vibrational spectra. The NIR FT-Raman and FT-IR spectra supported by the density functional theory (DFT) quantum chemical computations have been employed to analyze the effects of intramolecular charge transfer on the geometries and the vibrational modes contributing to the linear electro-optic effect of the organic NLO material. The calculated first hyperpolarizability of DMMC is 6.650 × 10 −30 esu, which is 25 times that of urea. The simultaneous IR and Raman activation of the phenyl ring modes of ν(C C/C–C) mode, ring C C stretching modes, in-plane deformation modes and the umbrella mode of methyl groups also provide evidences for the charge transfer interaction between the donors and the acceptor group through the π-system. Vibrational analysis indicates the electronic effects such as induction and back-donation on the methyl hydrogen atoms causing the lowering of stretching wavenumbers have also been analyzed in detail. The planar conformations would give an enhanced NLO activity where as any deviations from planarity would decrease the mobility of electrons within the π-conjugated molecular system, resulting a reduction in NLO activity.

Electronic, Optical, and Vibrational Properties of Bridged Dithienylethylene-Based NLO Chromophores

The vibrational, optical, and nonlinear optical (NLO) properties of a series of push−pull chromophores built around dithienylethylene-based π-conjugating spacers have been investigated by UV−vis, IR, and Raman spectroscopies and electric field-induced second harmonic generation (EFISH) measurements. The effects of the strength of the acceptor group on the molecular electronic properties of these conjugated NLO chromophores have been addressed. The magnitude of the intramolecular charge transfer has been tested as a function of the acceptor strength and of the bridging of the spacer. Density functional theory (DFT) calculations have been performed to help the assignment of the main electronic and vibrational features of the NLO chromophores and to derive useful information about their molecular structures. EFISH measurements show that push−pull systems that contain strong electron-acceptor groups connected via a rigidified dithienylene spacer exhibit large values of μβ0. Theoretical NLO calculations are in...

Efficient π electrons delocalization in prospective push–pull non-linear optical chromophore 4-[ N, N-dimethylamino]-4′-nitro stilbene (DANS): A vibrational spectroscopic study

A comprehensive investigation on the intramolecular charge transfer (ICT) of an efficient π-conjugated potential push–pull NLO chromophore, 4-[ N, N-dimethylamino]-4′-nitro stilbene (DANS), from a strong electron-donor group (dimethylamino- N(CH 3) 2) to a strong electron-acceptor group (nitro-NO 2) through the π-conjugated bridge ( trans-stilbene) has been carried out from their vibrational spectra. The NIR FT-Raman and FT-IR spectra supported by the density functional theory (DFT) quantum chemical computations have been employed to analyze the effects of intramolecular charge transfer on the geometries and the vibrational modes contributing to the linear electro-optic effect of the organic NLO material. It has been observed that the changes in the endocyclic and exocyclic angles result from the charge-transfer interaction of the phenyl ring and the amino group in the electron-donor side of the NLO chromophore. The strongest vibrational modes contributing to the electro-optic effect have been identified and examined from the concurrent IR and Raman activation of ν(C C/C–C) mode, ring C C stretching modes, in-plane deformation modes, nitro modes and the umbrella mode of methyl groups. Furthermore, the splitting of the vinyl stretching modes and the electronic effects such as hyperconjugation and backdonation on the methyl hydrogen atoms causing the decrease of stretching frequencies and infrared intensities have also been analyzed in detail. The effect of frontier orbitals transition of electron density transfer and the influence of planarity between the phenyl rings of the stilbene moiety on the first hyperpolarizability have also been discussed.

Electrical properties of organic light-emitting diodes using PECCP Langmuir–Blodgett films

Organic light-emitting diodes were fabricated using Langmuir–Blodgett (LB) technique with new emissive organic material. This new emissive organic material was synthesized and called PECCP [poly(3,6- N-2-ethylhexyl carbazolyl cyanoterephthalidene)], which has strong electron donor group and electron acceptor group in main chain repeated unit. This material has good solubility in common organic solvent and has a good stability in air. We made PECCP LB films and investigated current–voltage ( I– V) characteristics in ITO/PECCP LB/Al and ITO/PECCP LB/Alq 3/Al structures, and the Alq 3 was used as an electron transport layer. We have observed that the peak in electroluminescent spectrum of ITO/PECCP LB/Alq 3/Al device shifts to lower wavelength as the number of LB layer increases. The electroluminescent peaks are at about 507 nm, 505 nm, 503 nm, and 491 nm when the number of LB layers are 5, 7, 9, and 11 layers, respectively. From the I– V characteristics, the barrier height was obtained using Fowler–Nordheim analysis and it is in the range of 0.18 eV–0.26 eV.

Theoretical Study of Reactant Activation in 1,3-Dipolar Cycloadditions of Cyclic Nitrones to Free and Pt-Bound Nitriles

[reaction: see text] 1,3-Dipolar cycloaddition of the cyclic nitrones CH2(CH2)2CH=NO (N1), CH2CH2OCH=NO (N2), CH2-OCH2CH=NO (N3), and O(CH2)2CH=NO (N4) to organonitriles, RCN-both free (R = CH(3), CF(3)) and ligated to Pt(II) and Pt(IV) (in the complexes trans-[PtCl(2)(NCCH(3))(2)] (1) and trans-[PtCl(4)(NCCH(3))(2)] (2))-was investigated extensively by theoretical methods at different levels of theory. The effectiveness of two types of dipolarophile activation (by introducing a strong electron-acceptor group R and by coordination to a metal center) was analyzed and compared. The influence of factors such as the nature of the cyclic nitrone and the nature of the solvent on the reactions was also studied. The reactivity of dipoles and dipolarophiles increases along the series N4 < N1 approximately N3 < N2 and CH(3)CN < CF(3)CN < 1 < 2; the latter demonstrates that the coordination of RCN to a Pt center provides an even higher activation effect upon cycloaddition in comparison with the introduction of a strong electron-acceptor group R such as CF(3). A higher reactivity of the cyclic dipole N1 in comparison with acyclic nitrones (e.g., CH(3)CH=N(CH(3))O) is interpreted to be a result of its exclusive existence in a more strained and hence more reactive E- rather than Z-configuration. The activation and reaction energies have been calculated at different basis sets and levels of theory, up to MP4(SDTQ), CCSD(T), and CBS-Q. The activation energies are weakly sensitive to a change of the correlated methods. The consideration of the solvent effects results in the increase of the activation barriers, and such enhancement is less pronounced for the nonpolar or low polar solvents. The cycloadditions to CH(3)CN and CF(3)CN were found to be nearly synchronous, but these reactions involving 1 and 2 are clearly asynchronous. Moreover, the reaction of N2 with 2 proceeds via a very early acyclic transition state, while for all other reactions the transition states have a cyclic nature.

Preparation of Novel Push‐Pull Benzothiazole Derivatives with Reverse Polarity: Compounds with Potential Non‐Linear Optic Application.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Two Excited State Structures of Donor-Acceptor Substituted "Proton Sponge"

Photoexcitation of “proton sponge” 1,8-bis (dimethylamino) naphthalene (DMAN) leads to charge transfer (CT) emission. This work demonstrates that substitution of DMAN with a strong electron acceptor group (CN) results in CN-DMAN and leads to a stronger orbital decoupling between the Donor and Acceptor groups and to a more effective CT process (λF = 630 nm). The theoretical absorption spectrum calculated for CN-DMAN using the ZINDO method on its ground state ab initio [HF/6-31G(d)] optimized geometry reproduces a better experimental spectrum than that calculated using the RCIS method. It also shows that AM1 excited state (1La) optimization reveals two quasi-degenerated states with anti-quinoidal (A) and quinoidal (B) structures and the CT nature. Both structures may contribute more or less equally to the fluorescence of CN-DMAN in a solution.