A novel approach to synthesis of tricyanovinylthiophene for heterocyclic imidazole nonlinear optical chromophores

Multicomponent synthesis of chromophores – The one-pot approach to functional π-systems

Multicomponent reactions, conducted in a domino, sequential or consecutive fashion, have not only considerably enhanced synthetic efficiency as one-pot methodology, but they have also become an enabling tool for interdisciplinary research. The highly diversity-oriented nature of the synthetic concept allows accessing huge structural and functional space. Already some decades ago this has been recognized for life sciences, in particular, lead finding and exploration in pharma and agricultural chemistry. The quest for novel functional materials has also opened the field for diversity-oriented syntheses of functional π-systems, i.e. dyes for photonic and electronic applications based on their electronic properties. This review summarizes recent developments in MCR syntheses of functional chromophores highlighting syntheses following either the framework forming scaffold approach by establishing connectivity between chromophores or the chromogenic chromophore approach by de novo formation of chromophore of interest. Both approaches warrant rapid access to molecular functional π-systems, i.e. chromophores, fluorophores, and electrophores for various applications.

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

New Y-shaped ferrocene conjugated imidazole chromophores were prepared and fully characterized. The Y-shaped structure was confirmed by the single crystal X-ray diffraction technique. The chromophores show interesting second-order nonlinear optical (NLO) properties in solution, as determined by the Electric-Field Induced Second Harmonic generation (EFISH) technique. Remarkably, the trifluoro substituted compound 3 is characterized by a high μβEFISH value and has good potential as a molecular building block for composite films with Second Harmonic Generation (SHG) properties. For all compounds, the dipole moments and frontier orbital energies were calculated by the Density Functional Theoretical method.

Structure and Reactivity of Highly Twisted N-Acylimidazoles

A modular and efficient synthesis of highly twisted N-acylimidazoles is reported. These twist amides were characterized via X-ray crystallography, NMR spectroscopy, IR spectroscopy, and DFT calculations. Modification of the substituent proximal to the amide revealed a maximum torsional angle of 88.6° in the solid state, which may be the most twisted amide reported for a nonbicyclic system to date. Reactivity and stability studies indicate that these twisted N-acylimidazoles may be valuable, namely as acyl transfer reagents.

Crystal structure of ethyl 2-[2-(4-methyl-benzo-yl)-5-p-tolyl-1H-imidazol-1-yl]acetate

In the title compound, C22H22N2O3, the plane of the five-membered ring is oriented at dihedral angles of 45.4 (1) and 52.5 (1)° to the phenyl rings. Furthermore, this ring makes an angle of 85.2 (2)° with the plane of the ethyl acetate substituent. The mol-ecular structure is affected by an intra-molecular C-H⋯O hydrogen bond between an H atom from the p-tolyl group and the carbonyl O atom of the acetate. The methyl group of the ethyl acetate residue is disordered over two sites with equal occupancies. The crystal structure features inter-molecular C-H⋯O and C-H⋯N inter-actions. One of the C-H⋯O hydrogen bonds forms a C(5) chain motif extending along the a axis. In addition, C-H⋯N contacts form inversion dimers with R 2 (2)(12) ring motifs, linking the imidazole ring system to the benzene ring of the p-tolyl substituent.

Kamlet-Taft and Catalán solvatochromism of some π-expanded phenanthrimidazole derivatives - DFT analysis

Some π-expanded phenanthrimidazole derivatives have been synthesised and characterised by different spectral techniques. Kamlet-Taft and Catalán solvatochromism of synthesised phenanthrimidazole derivatives have been analysed. Non-linear optical (NLO) and natural bond orbital (NBO) analysis have been made by ab initio method to show intramolecular interactions. The energies of the HOMO and LUMO levels, the molecular electrostatic potential (MEP) energy surface, NBO studies have exploited the existence of intramolecular charge transfer (ICT) within the molecule.

Optical properties of 1,2-diaryl benzimidazole derivatives - a combined experimental and theoretical studies

Some novel 1,2-diaryl benzimidazole derivatives have been designed, synthesized and characterized by mass, (1)H, (13)C-NMR spectral studies and single crystal XRD. The charge distribution has been calculated from the atomic charges by non-linear optical (NLO) and natural bond orbital (NBO) analyses have been calculated by abinitio method. Synthesized 1,2-diaryl benzimidazole derivatives have the largest μgβ0 value and can be used as potential NLO materials. Analysis of the molecular electrostatic potential (MEP) energy surface exploited the region for non-covalent interactions in the molecule. Calculated bond lengths, bond angles and dihedral angles are found to be slightly higher than that of X-ray diffraction values of its experimental datas.

1-(4-Methyl-phen-yl)-2-[4-(trifluoro-methyl)phen-yl]-1H-phenanthro[9,10-d]imida-zole

In the title compound, C29H19F3N2, the tetra-cyclic ring system is essentially planar [maximum deviation from the best plane = 0.076 (1) Å] and makes dihedral angles of 78.10 (5) and 33.71 (4)° with the methyl-phenyl and fluoro-phenyl rings, respectively. An intra-molecular C-H⋯π inter-action occurs. In the crystal, pairs of C-H⋯π inter-actions link inversion-related mol-ecules.

Computational studies of 1,2-disubstituted benzimidazole derivatives

Some 1,2-disubstituted benzimidazole derivatives (1-6) have been synthesized and characterized by mass, (1)H, (13)C NMR and elemental analysis. XRD analysis was carried out for 1-(4-methylbenzyl)-2-p-tolyl-1H-benzo[d]imidazole. Calculated bond lengths, bond angles and thus dihedral angles are found to be slightly higher than that of X-ray diffraction values of its experimental data. The charge distribution has been calculated from the atomic charges by non-linear optical (NLO) and natural bond orbital (NBO) analyses have been calculated by ab initio method. Since the synthesized 1,2-disubstituted benzimidazole derivatives have the largest μ(g)β(0) value and can be used as potential NLO materials. Analysis of the molecular electrostatic potential (MEP) energy surface exploited the region for non-covalent interactions in the molecule. Atom in molecule analysis (AIM) was carried out to show the presence of bond critical points (BCPs).

Characterization, photophysical and DFT calculation study on 2-(2,4-difluorophenyl)-1-(4-methoxyphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline ligand

The synthesized imidazole derivative 2-(2,4-difluorophenyl)-1-(4-methoxyphenyl)-1H-imidazo[4,5-f][1,10] phenanthroline (dfpmpip) has been characterized using IR, mass, (1)H, (13)C NMR and elemental analysis. The photophysical properties of dfpmpip have been studied using UV-visible and fluorescence spectroscopy in different solvents. The solvent effect on the absorption and fluorescence bands has been analyzed by a multi-component linear regression. Theoretically calculated bond lengths, bond angles and dihedral angles are found to be slightly higher than that of X-ray Diffraction (XRD) values of its parent compound. The charge distribution has been calculated from the atomic charges by non-linear optical (NLO) and natural bond orbital (NBO) analysis. Since the synthesized imidazole derivative has the largest μ(g)β(0) value, the reported imidazole can be used as potential NLO material. The energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels and the molecular electrostatic potential (MEP) energy surface studies evidenced the existence of intramolecular charge transfer (ICT) within the molecule. Theoretical calculations regarding the chemical potential (μ), hardness (η) and electrophilicity index (ω) have also been calculated.

2-(4-Fluoro-phen-yl)-1-phenyl-1H-benzimidazole

In the title mol-ecule, C(19)H(13)FN(2), the benzimidazole unit is close to planar [maximum deviation = 0.0342 (9) Å] and forms dihedral angles of 58.94 (3) and 51.43 (3)° with the phenyl and fluoro-benzene rings, respectively; the dihedral angle between the phenyl and fluoro-benzene rings is 60.17 (6)°. In the crystal, three C-H⋯F hydrogen bonds and two weak C-H⋯π inter-actions involving the fused benzene ring lead to a three-dimensional architecture.

Imidazole as a parent π-conjugated backbone in charge-transfer chromophores

Research activities in the field of imidazole-derived push-pull systems featuring intramolecular charge transfer (ICT) are reviewed. Design, synthetic pathways, linear and nonlinear optical properties, electrochemistry, structure-property relationships, and the prospective application of such D-π-A organic materials are described. This review focuses on Y-shaped imidazoles, bi- and diimidazoles, benzimidazoles, bis(benzimidazoles), imidazole-4,5-dicarbonitriles, and imidazole-derived chromophores chemically bound to a polymer chain.

Synthesis and characterization of the ground and excited states of tripodal-like oligothienyl-imidazoles

Six new thiophene oligomers, here designated as tripodal-like oligothienyl-imidazoles, were synthesized and have been investigated in ethanol solution at room and low temperature. The oligomers bear a common core where two or more thiophenes are linked to one or more imidazole units that further links through its alpha-position to a different number of incremental thiophene units. The study involves a comprehensive spectral and photophysical investigation where the properties of the singlet and triplet states have been investigated regarding absorption, fluorescence and phosphorescence, transient triplet-triplet absorption together with all relevant quantum yields (fluorescence, phi(F), internal conversion, phi(IC), intersystem crossing, phi(T,) and singlet oxygen, phi(Delta)) and lifetimes. In addition, density functional theory quantum chemical calculations were performed to gain a detailed understanding of the molecular geometry and optical properties of the investigated oligomers. From the overall data, the radiative (k(F)) and radiationless (k(NR), k(IC), and k(ISC)) rate constants have been determined and it is shown that, in contrast with the parent oligothiophenes, the radiative competes with the radiationless deactivation channels. The results show that, by comparison with the oligothiophene counterparts, there is an augment of the relative contributions of the internal conversion and fluorescence processes relative to the S(1)~~-->T(1) intersystem crossing. Phosphosphorescence emission was found for the simplest member of the investigated compounds with a low quantum yield (phi(Ph) = 0.009) and a lifetime of 8 micros. The data also show that the introduction of a 4,5-dithienyl-imidazole moiety in a bi- or terthiophene oligomer results in, respectively, a 20-fold and a 3-fold increase of the fluorescence quantum yield relative to their oligothiophene counterparts. The synergy of the structural and photophysical properties, combined with the exceptional thermal stabilities, opens new perspectives related to the copolymerization of oligothiophenes with thienyl-imidazole units with potential application as organic light emitting devices.

1-Alkyl-1H-imidazole-based dipolar organic compounds for dye-sensitized solar cells

A series of donor-pi-acceptor-type organic dyes based on 1-alkyl-1H-imidazole spacers 1-5 have been developed and characterized. The two electron donors are at positions 4 and 5 of the imidazole, while the electron-accepting cyanoacrylic acid is incorporated at position 2 by a spacer-containing heteroaromatic rings, such as thiophene and thiazole. Detailed investigation on the relationship between the structure, spectral and electrochemical properties, and performance of DSSC is described here. Dye-sensitized solar cells (DSSCs) using dyes as the sensitizers exhibit good efficiencies, ranging from 3.06 to 6.35 %, which reached 42-87 % with respect to that of N719-based device (7.33 %) fabricated and measured under similar conditions. Time-dependent density functional theory (TDDFT) calculations have been performed on the dyes, and the results show that both electron donors can contribute to electron injection upon photo-excitation, either directly or indirectly by internal conversion to the lowest excited state.

Y-shaped two-photon absorbing molecules with an imidazole–thiazole core

Two new classes of two-photon absorbing Y-shaped molecules have been developed to possess an imidazole-thiazole core and a stilbene-type conjugation pathway with either nitro or sulfonyl as terminal electron-accepting group.

Crystal structure of 4,5-bis(4-dimethylaminophenyl)-2-(4-nitrophenyl)imidazole

A nonlinear optical chromophore, 4,5-bis(4-dimethylaminophenyl)-2-(4-nitrophenyl)imidazole, was investigated by X-ray crystallography. The study focused on coplanarity among several aromatic rings, including phenyls and imidazole. Two phenyl rings with NMe2 groups are twisted by 46.39(3) degrees from each other. However, they are twisted by 23.05(5) degrees and 46.84(3) degrees from the imidazole, respectively. These unequal twists were elucidated by different conjugation pathways from the donors to the acceptor. The phenyl ring with the NO2 group is twisted by only 6.76(6) degrees from the imidazole.