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The utilization of photodynamic therapy (PDT) has been rapidly increasing due to its advantage as an effective treatment modality for cancer. The organic photosensitizers employed for PDT have some disadvantages, including high toxicity, non-selectivity toward tumors and poor absorption of light. The low light penetration into the tumor sites resulting from low wavelength of absorption and long-term skin photosensitivity. Hence, the attention toward non-toxic inorganic photosensitizers like noble metal nanoparticles (NPs) has been increasing nowadays. In bioscience, NPs are replacing organic dyes since they have photostability and non-toxicity. Generally, nanomaterials can easily form compounds with other substances as well as organic materials and the modified NPs surface enhances the chemical activity. Among the metal NPs, noble metals, especially gold and silver are attractive because of their size and shape-dependent unique optoelectronic properties. The coating of inorganic/organic materials on top of the noble metal makes the NPs bio-compatible and less toxic. Furthermore, Ag- and Au-based inorganic/organic complex NPs could offer a new possibility because of their unique structures. Meanwhile, the coating of inorganic/organic complex NPs protects the noble metals and stabilizes them against chemical corrosion and enhances the production of reactive oxygen species. Thus, in this review, we have highlighted the role of Ag- and Au-based inorganic/organic hybrid nano-photosensitizers in photodynamic therapy.Communicated by Ramaswamy H. Sarma.

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The antibacterial and antifungal effects of non-functionalized and surface-functionalized Mn3O4 nanoparticles were comparatively analyzed to reason out the potential changes in antimicrobial activities due to functionalization with 5-amino-2-mercapto benzimidazole (AMB) molecule. The surface functionalization of Mn3O4 nanoparticles with AMB molecule was confirmed by the XRD result, which shows the shift in 2θ values with noticeable peaks. The surface morphology and functionalization of Mn3O4 nanoparticles were additionally confirmed by HR-SEM and EDAX studies. Antimicrobial activities were investigated by an agar-well-diffusion method using the bacteria Staphylococcus aureus and Pseudomonas aeruginosa and fungi Aspergillus niger. The functionalized Mn3O4 nanoparticles possess remarkable antibacterial and antifungal effect than the non-functionalized Mn3O4 nanoparticles and AMB molecule. The coating of low energy surface layer over metal oxide nanoparticles such as Mn3O4 offers an active surface toward both transfer of electron and the adsorption or desorption of water, inorganic ions, and other molecules, which leads to the increased antimicrobial activity of f-Mn3O4 nanoparticles.Communicated by Ramaswamy H. Sarma.

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Herein, the work addresses the synthesis of biomaterials (chitosan and garlic) loaded CdO-TiO2 hybrid nanocomposites for photocatalytic water treatment and photodynamic cancer therapeutic applications that were reported the first time. CdO-TiO2 (CT) nanocomposites were synthesized and loaded with the biomaterials such as chitosan and garlic by simple sol-gel method. The nanomaterials were characterized and the photodegradation of three model pollutants, Methylene blue (MB), Methyl orange (MO) and Rhodamine B (Rh-B) was opted to investigate the efficiency of the synthesized photocatalyst under the solar light. From the results, the garlic-loaded CdO-TiO2 (AS-CT) hybrid nanocomposites exhibit a superior photocatalytic activity than the chitosan-loaded CdO-TiO2 (CS-CT) and CdO-TiO2 (CT) nanocomposites under the irradiation of solar light. Additionally, the cell viability of the synthesized nanocomposites was carried out in HeLa cell lines under different concentrations, light doses and incubation periods using an LED light source. Compared to the CS-CT and CT nanocomposites, an efficient photodynamic activity was achieved in the case of AS-CT hybrid nanocomposites. Actually, the end-use properties required for both processes in AS-CT nanocomposites appear similar due to the presence of organo sulphurus compounds.

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With recent scientific developments, Photodynamic therapy (PDT) offers the promisie to become incorporated into the mainstream of cancer therapy. Noble metal based nano-PDT is increasing due to its advantages in the field of biomedicine. In this study, noble metal based Ag@SiO2 core-shell nanoparticles were synthesized and to confirm the core-shell structure they were characterized by UV-vis, XRD, FTIR, TEM, and EDX. Our data confirm that core-shell type Ag@SiO2 nanoparticles maintain its ability to kill cancer cells upon light irradiation. This shows that SiO2 shell may not only prevent aggregation but it also may enhance the photodynamic activity of Ag nanoparticles.

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Metal-semiconductor core-shell type Pd@SiO2 nanoparticles (NPs) were successfully synthesized by Stober's method and the product was characterized by UV-vis, XRD, FT-IR, SEM, HR-TEM and EDX techniques. In vitro Photodynamic activity and DNA binding studies of Pd@SiO2 core shell nanoparticles were studied. Cell viability of the core-shell nanoparticles against HeLa cell line was screened by MTT assay after exposing at different light doses. The outcome of the present study indicates that the core-shell Pd@SiO2 NPs are highly stable and exhibited strong photodynamic efficiency under LED light illumination in HeLa cells. The results indicated that SiO2 supported on the surface of Pd NPs not only prevented the aggregation in addition exhibited remarkable photodynamic activity.

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In this article a series of epoxy nanocomposites film were developed using amine functionalized (ZnO-APTES) core shell nanoparticles as the dispersed phase and a commercially available epoxy resin as the matrix phase. The functional group of the samples was characterized using FT-IR spectra. The most prominent peaks of epoxy resin were found in bare epoxy and in all the functionalized ZnO dispersed epoxy nanocomposites (ZnO-APTES-DGEBA). The XRD analysis of all the samples exhibits considerable shift in 2θ, intensity and d-spacing values but the best and optimum concentration is found to be 3% ZnO-APTES core shell nanoparticles loaded epoxy nanocomposites supported by FT-IR results. From TGA measurements, 100wt% residue is obtained in bare ZnO nanoparticles whereas in ZnO core shell nanoparticles grafted DGEBA residue percentages are 37, 41, 45, 46 and 52% for 0, 1, 3, 5 and 7% ZnO-APTES-DGEBA respectively, which is confirmed with ICP-OES analysis. From antimicrobial activity test, it was notable that antimicrobial activity of 7% ZnO-APTES core shell nanoparticles loaded epoxy nanocomposite film has best inhibition zone effect against all pathogens under study.

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Metal-semiconductor core-shell type Au@SiO2 nanoparticles were prepared by Stober's method. They were characterized by absorption, XRD, HR-TEM and EDAX techniques. The resulting modified core-shell nanoparticles shows that the formation of singlet oxygen, which was confirmed by ESR technique. The photohemolysis studies were carried out under two different experimental conditions. It is observed that the photohemolysis increases with concentration as well as light dose. Cell viability of the core-shell nanoparticles against HeLa cell lines were studied by MTT assay method. The outcomes of the present study indicate that, the Au@SiO2 core-shell nanoparticles are extremely stable with a very high photodynamic efficiency under visible light illumination.

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Multicomponent, highly efficient, catalytic synthesis of some polysubstituted imidazole under solvent-free condition is reported. Characterization of polysubstituted imidazole have been carried out by X-ray diffraction (XRD) and spectral techniques. Electronic spectral studies reveal that their solvatochromic behavior depends not only on the polarity of the medium but also on the hydrogen bonding properties of the solvents. Specific hydrogen bonding interaction in polar solvents modulated the order of the two close lying lowest singlet states. The solvent effect on both the absorption and emission spectral results have been analyzed by multiple parametric regression analysis. Solvatochromic effects on the emission spectral position indicate the charge transfer (CT) character of the emitting singlet states both in a polar and a non polar environment. The fluorescence decays for the imidazole fit satisfactorily to a single exponential kinetics. The prototropic studies of N,N-dimethyl-4-(1,4,5-triphenyl-1H-imidazol-2-yl)naphthalen-1-amine (DTINA) reveal that two monocations [imidazole nitrogen protanated (MC1) and dimethylamino nitrogen protanated (MC2)] and a dication [both imidazole nitrogen and dimethylamino nitrogen protanated (DC)] are formed by protonation in both ground and excited states. These observations are in consistent with quantum chemical calculations.

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A set of π-expanded imidazole derivatives employing excited state intramolecular proton transfer (ESIPT) was designed and synthesized. The relationship between the structure and photophysical properties were thoroughly elucidated by comparing with the analogue blocked with ESIPT functionality. The compound possessing an acidic NH function as part of an intramolecular hydrogen bond system has much higher fluorescence quantum yield and Stokes shift and the π-expansion strongly influences the optical properties. The occurrence of ESIPT for imidazole tosylamide derivatives were less affected by the hydrogen-bonding ability of the solvents compared to the unprotected amine. The low pKa values for the monocation ⇌ neutral equilibrium indicate the presence of intramolecular hydrogen bonding between the amino proton and tertiary nitrogen atom.

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A fluorophore 2-(naphthalen-1-yl)-1,4,5-triphenyl-1H-imidazole [NTI] has been designed, synthesized and characterized by (1)H NMR, (13)C NMR, mass and single crystal XRD. Absorption, emission, lifetime and cyclic voltammetry have been made to deduce the interaction between NTI and ZnO and Bi2O3 nanocrystals. NTI act as a new host for ZnO and Bi2O3 nanocrystals that enhance its luminescence. The apparent binding constant has been obtained. Adsorption of the NTI on ZnO and Bi2O3 nanocrystals lowers the HOMO energy level of the NTI. The strong adsorption of the NTI on the surface of ZnO and Bi2O3 nanocrystals is likely due to the chemical affinity of the nitrogen atom of the NTI to the zinc ion on the surface of nanocrystals. SEM and EDS spectra confirmed the adsorption of NTI on the surface of nanocrystals.

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Photophysical and electrochemical studies of cyclometalated cationic heteroleptic iridium(III) complex salts have been carried out. For these complex salts the intense absorption bands appeared around 263 nm and are assigned to spin-allowed π-π* transitions of phenanthroline ligands. Moderately intense and weak absorption bands observed around 341 and 440 nm, respectively. These bands are assigned to spin-allowed metal to ligand charge transfer (1)MLCT and (3)MLCT transitions, respectively. The influence of anions and proton on the photophysical and electrochemical studies were also carried out. The emission wavelength was red shifted and emission color changed from yellow to red by the addition of CF3CO2H. The solution color changed from green to brown and the emission was quenched by the addition anions such as of F(-), CH3COO(-) and H2PO4(-).

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Multicomponent, one-pot, highly efficient, indium trifluoride (InF3) catalytic synthesis of 2-(naphthalen-1-yl)-4,5-diphenyl-1H-imidazole under solvent-free condition is reported. Characterization of imidazole has been carried out by spectral techniques. The synthesized phosphated imidazole (PI) and phosphated imidazole bound magnetic nanoparticles (PIBMN) were characterized using Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and powder X-ray diffraction (XRD). The photophysical characteristics of the synthesized phosphated imidazole and phosphated imidazole bound magnetic nanoparticles were investigated by steady-state absorption and emission spectroscopy as well as time resolved fluorometry. From these experiments, the position of the spectral maxima (λabs, λexc and λemi), and lifetime (τ) of the synthesized phosphated imidazole and phosphated imidazole bound magnetic nanoparticle have been determined.

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This article presents optical, electrochemical, and thermal properties of novel class of green fluorescent 1-(4,5-diphenyl-1-p-tolyl-1H-imidazol-2-yl)naphthalen-2-ol. Detailed photo physical and quantum chemical studies have been performed to elucidate the excited state intramolecular proton transfer (ESIPT) reaction leading a large stokes shifted fluorescence emission from the phototautomer. The results of quantum chemical investigations confirmed the intramolecular charge transfer characteristics of the ESIPT tautomers. The high photoluminescence quantum yield is ascribed to twisted chromophores due to phenyl substituents at 1,2-position of the imidazole ring which restricted intramolecular motion, leading to an optically allowed lowest optical transition without self quenching.

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A new fluorophore 2-(4-fluorophenyl)-1-phenyl-1H-phenanthro [9,10-d]imidazole has been synthesized and characterized by spectroscopic techniques. Nanoparticulate ZnO enhances the fluorescence of the synthesised fluorophore. The absorption, fluorescence, lifetime, cyclic voltammetry and infrared studies reveal that fluorophore is attached to the surface of ZnO semiconductor. Photo-induced electron transfer (PET) explains the enhancement of fluorescence by nanoparticulate ZnO and the apparent binding constant has been obtained. Adsorption of the fluorophore on ZnO nanoparticle lowers the HOMO and LUMO energy levels of the fluorophore. The strong adsorption of the phenanthrimidazole derivative on the surface of ZnO nanocrystals is likely due to the chemical affinity of the nitrogen atom of the organic molecule to the zinc ion on the surface of nanocrystal.

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Some fluorescent benzimidazole derivatives have been designed and synthesized using cobalt(ii) hydroxide as highly efficient catalyst. Synthesized compounds have been characterized by (1)H and (13)C-NMR and mass spectral analysis. The solvent effect on the absorption and fluorescence bands has been analyzed and supplemented by computational studies. Solvatochromic effects on the spectral position and profile of the stationary fluorescence spectra clearly indicate the charge transfer (CT) character of the emitting singlet states of all of the compounds studied in both polar and non-polar environments. The fluorescence decays for the benzimidazoles fit satisfactorily to a single exponential kinetics. HOMO and LUMO orbital pictures [DFT/B3LYP/6-31G(d,p)] evidence the existence of excited state intramolecular proton transfer (ESIPT) in benzimidazole derivatives containing a hydroxy group.

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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 µgß0 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.

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1-Benzyl-2-phenyl-1H-benzo[d]imidazole (BPBI) has been synthesized by simple steps and characterized by spectral studies. Absorption and fluorescence spectral studies have been employed to investigate the interaction of BPBI with the anatase, hombikat, P25 and rutile phases of TiO2. The emission of the BPBI is efficiently quenched by anatase, hombikat and P25 TiO2 nanoparticles owing to charge injection from the excited singlet state of BPBI to the conduction band of the TiO2 nanoparticles. Surprisingly, rutile phase enhances the fluorescence which is likely due to lowering of LUMO and HOMO levels of the ligand on ducking of the benzimidazole moiety of the BPBI molecule into the void space of rutile TiO2. Electron injection from photoexcited BPBI to the TiO2 conduction band (S*→S(+)+e(-)(CB)) is likely to enhance the fluorescence.

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A new kind of fluorophore 2-(4-fluorophenyl)-1-phenyl-1H-benzo[d]imidazole (FPPBI) has been synthesized and characterized by (1)H NMR, (13)C NMR, mass spectral studies and single crystal XRD. The energy transfer from FPPBI to Al2O3 nanocrystals has been studied by absorption, fluorescence and lifetime spectroscopic methods. The association between nanoparticles and FPPBI is explained from both absorption and fluorescence quenching data. The distance between FPPBI and Al2O3 as well as the critical energy transfer distance has been deduced.

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In the title mol-ecule, C19H14N2O, the benzimidazole unit is close to being planar [maximum deviation = 0.0253 (11) Å] and forms dihedral angles of 68.98 (6) and 20.38 (7)° with the adjacent phenyl and benzene rings; the dihedral angle between the latter two planes is 64.30 (7)°. An intra-molecular O-H⋯N hydrogen bond generates an S(6) ring motif. In the crystal, mol-ecules are linked by C-H⋯N and C-H⋯O hydrogen bonds, and consolidated into a three-dimensional architecture by π-π stacking inter-actions, with a centroid-centroid distance of 3.8428 (12) Å.

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In the title compound, C20H16N2, the benzimidazole ring system forms dihedral angles of 28.50 (7) and 72.44 (7)° with the tolyl and phenyl rings, respectively. In the crystal, mol-ecules are linked into chains along the a-axis direction by weak C-H⋯N inter-actions. The crystal structure also features C-H⋯π inter-actions.