P. Ramanathan

Photophysical properties of the intramolecular excited charge-transfer states of π-expanded styryl phenanthrimidazoles – effect of solvent polarity

Correction for ‘Photophysical properties of the intramolecular excited charge-transfer states of π-expanded styryl phenanthrimidazoles – effect of solvent polarity’ by V. Thanikachalam et al., RSC Adv., 2014, 4, 6790–6806.

Optical and theoretical studies on Fe3O4–imidazole nanocomposite and clusters

N,N-Dimethyl-4-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-1-amine (DMPPINA) has been synthesised using sol–gel prepared TiO2 rutile as a catalyst under solvent free conditions and characterized by NMR spectral studies. The synthesised phenanthrimidazole bound magnetic nanoparticles (Fe3O4–DMPPINA composite) have been characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffractometry (XRD) and lifetime and Fourier-transform infrared spectroscopies (FT-IR). The intensities of absorption and emission of the Fe3O4–DMPPINA composite is higher than DMPPINA. Conductance and VSM measurements were also carried out. The prototropic study of DMPPINA has been made to show the increase of electron density at the azomethine nitrogen atom due to charge transfer from the N,N-dimethylamino group to the azomethine nitrogen atom. The molecular electrostatic potential surface (MEP) has also been employed to show the higher electron density at the azomethine nitrogen atom. Theoretical investigation shows that the calculated binding energy and energy gap of the imidazole composite are highly dependent on the nature of the iron oxide cluster. We have studied in detail the site-specific binding nature and the adsorption strength of imidazole with different iron oxide clusters.

Binding and fluorescence enhancing behaviour of phenanthrimidazole with different phases of TiO2

Photoinduced intramolecular charge transfer (ICT) in a series of a newly synthesized 1H-phenanthro[9,10-d]imidazoles containing electron donor–acceptor fragments have been studied. The effect of solvents on the fluorescence spectra indicates the CT character of emitting singlet states and analysis of CT fluorescence accounts the electron transfer in the Marcus inverted region. Nanocrystalline anatase and rutile phases of TiO2 were obtained by the sol–gel method, characterized by X-ray diffraction, high resolution scanning electron microscopy, transmission electron microscopy and energy dispersive, UV-visible diffuse reflectance, and solid photoluminescence spectroscopies. TiO2 Hombikat was supplied by fluka. TiO2 P25 was a gift from Degussa. Absorption, fluorescence and lifetime spectral studies, and cyclic voltammetric analysis have been employed to investigate the interaction of TPIN with TiO2 (A), TiO2 (H), TiO2 (P25) and TiO2 (R). The fluorescence of TPIN is efficiently quenched by TiO2 (A), TiO2 (H) and TiO2 (P25) nanoparticles owing to charge injection from the excited singlet state of TPIN to the conduction band of the TiO2 nanoparticles. However, TiO2 (R) enhances the fluorescence due to lowering of LUMO and HOMO levels of TPIN.

Intramolecular excited proton transfer of 1-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-2-ol – A combined experimental and quantum chemical studies

Synthesis of the 1-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-2-ol [PPIN] is reported, spectral and fluorescent properties of the title compound are investigated. The feasibility of excited state intramolecular proton transfer (ESIPT) has been argued from the changeover of relative stability of the enol and the keto forms on photoexcitation from the S0-PES to the S1-PES. Critical evaluation on the modulations of geometrical parameters other than the proton transfer reaction coordinate has also been undertaken. The intramolecular hydrogen bonding (IMHB) interaction in PPIN has been explored by calculation of the hyperconjugative charge transfer interaction from the lone electron pair of ring nitrogen atom to the σ(∗) orbital of O-H bond, under the provision of Natural Bond Orbital (NBO) analysis. However, DFT calculations together with the experimental results reveal that the excited species with the intramolecular N⋯HO hydrogen bond type undergoes rapid radiationless deactivation. This leads to a conclusion that the low-intensity dual-band fluorescence of the title compound in solution originates from the traces of the conformation with the -OH bond to azomethine nitrogen atom (ESIPT).

Structural, Electronic and Charge Transfer Studies of Highly Sensitive Fluorescent Probe 2-((E)-2-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)phenol: Quantum Chemical Investigations

This article presents a facile synthesis of novel class of bluish-green fluorescent 2-((E)-2-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)phenol [PPIVP] and their optical, electrochemical and thermal properties. Detailed photophysical and quantum chemical studies have been performed to elucidate the origin of the dual emission shifts. PPIVP undergo excited state intramolecular proton transfer (ESIPT) reaction leading a large Stoke’s shifted fluorescence emission from the phototautomer. The results of quantum chemical investigations not only confirmed the intramolecular charge transfer characteristics of the ESIPT tautomers but also provided a rational for the observed high fluorescence quantum efficiency in the solid state. The high photoluminescence quantum yield in the solid state is ascribed to twisted chromophores due to phenyl substituents at 1,2-position of the phenanthroimidazole ring which restricted intramolecular motion, leading to an optically allowed lowest optical transition without self quenching.

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.

Phenanthrimidazole as a fluorescent sensor with logic gate operations.

A novel sensor namely, 1-(1-(p-tolyl)-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-2-ol was synthesised for the detection of anion as well as cation through intramolecular charge transfer mechanism. This compound was used for the selective detection of Zn(2+) ion as compared to other metal ions and the binding was evidenced from the new absorption band at 356 nm and switch on fluorescence at 453 nm. The switch on fluorescence can be explained on the basis of photoinduced electron transfer (PET) mechanism and it was demonstrated by logic gate functions.

Synthesis and optical properties of phenanthromidazole derivatives for organic electroluminescent devices

Five phenanthromidazole derivatives, namely 2-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazole (1), 2-(naphthalen-1-yl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (2), 2-(naphthalen-1-yl)-1-p-tolyl-1H-phenanthro[9,10-d]imidazole (3), 1-(4-methoxyphenyl)-2-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazole (4) and 1-(3,5-dimethylphenyl)-2-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazole (5), were synthesised using the TiO2 (R) nanosemiconductor as the catalyst under solvent free conditions and characterised by NMR and single crystal XRD techniques. Their photophysical, electrochemical and electroluminescent properties were carefully analysed. Highly efficient Alq3-based organic light emitting devices have been developed using phenanthromidazoles as functional layers between NPB [4,4-bis(N-(1-naphthyl)-N-phenylamino)biphenyl] and Alq3 [tris(8-hydroxyquinoline)aluminium] layers. Using the device of ITO/NPB/4/Alq3/LiF/Al, a maximum luminous efficiency of 5.99 cd A−1 was obtained with a maximum brightness of 40 623 cd m−2 and a power efficiency of 5.25 lm W−1.

Enhancing the photoluminescence of 1-(naphthalene-1-yl)-2,4,5-triphenyl-1H-imidazole anchored to superparamagnetic nanoparticles.

Synthesis and characterization of 1-(naphthalene-1-yl)-2,4,5-triphenyl-1H-imidazole has been carried out by spectral studies. The synthesized phosphated imidazole and phosphated imidazole bound magnetic nanoparticles 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 spectra as well as time resolved fluorometry. The intensities of absorption and emission maxima increase in the following order, phosphated imidazole bound Fe2O3>phosphated imidazole>imidazole.

Nano rutile TiO2 catalysed synthesis of (E)-4-(2-(1-(4-chlorophenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)-N,N-dimethylaniline and its interaction with super paramagnetic nanoparticles

The synthesis of (E)-4-(2-(1-(4-chlorophenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)-N,N-dimethylaniline (CPPIVI) has been carried out using TiO2 (R) as catalyst under solvent free conditions and characterized by NMR spectral studies. The catalyst was characterized by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The catalyst is reusable with satisfactory results. The synthesised phosphated styrylimidazole (PSI) and phosphated styrylimidazole bound magnetic nanoparticles (PSIMN) were characterized using SEM, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), XRD and Fourier-transform infrared spectroscopy (FT-IR). The intensities of the absorption and emission maxima are of the following order: PSIMN > PSI > CPPIVI. Conductance and VSM measurements were also carried out. The lifetime of the excited states of PSIMN, PSI and CPPIVI has been obtained. A prototropic study of CPPIVI has also been made at different concentrations.