R. Sathishkumar

Fluorescence investigation of the interaction of 2-(4-fluorophenyl)-1-phenyl-1H-phenanthro [9,10-d] imidazole with bovine serum albumin

The interaction between 2-(4-fluorophenyl)-1-phenyl-1H-phenanthro [9,10-d] imidazole (FPPI) and bovine serum albumin (BSA) was investigated by fluorescence spectral studies. The observed experimental result shows that the imidazole derivative has strong ability to quench the fluorescence of BSA by forming complex which is stabilized by electrostatic interactions. The effective quenching constants (K(sv)) were 2.78 × 10(4), 2.52 × 10(4), and 2.32 × 10(4) at 301, 310, and 318 K respectively. The Stern-Volmer quenching constant (K(sv)), binding site number (n), apparent binding constant (K(A)) and corresponding thermodynamic parameters (ΔG, ΔH, and ΔS) were calculated. The distance between the donor (BSA) and acceptor (FPPI) was obtained according to fluorescence resonance energy transfer (FRET). Conformational changes of BSA were observed from synchronous fluorescence technique. The effect of metal ions such as Cu(2+), Zn(2+), Ca(2+), Mg(2+), Ni(2+), Co(2+), and Fe(2+) on the binding constants between the FPPI and BSA were also studied.

Selective quenching of benzimidazole derivatives by Cu2+ metal ion

It is a very big challenge to develop a Cu(2+) selective fluorescent sensor with the ability to exclude the interference of some metal ions such as Fe(3+), Mg(2+), Ag(+), K(+) and Na(+). Herein, we report a fluorescence quenching of some benzimidazole derivatives (1-6) with Cu(2+) metal ion. These benzimidazole derivatives have been shown to bind copper ions resulting in quenching of its fluorescence. The response to Cu(2+) is rapid, selective and reversible upon addition of a copper chelator. These benzimidazole derivatives were characterized by (1)H, (13)C NMR mass and elemental analysis. XRD analysis was carried out for 1-(4-methylbenzyl)-2-p-tolyl-1H-benzo[d]imidazole.

Fluorescence quenching of bovine serum albumin by NNMB

A new type of fluorophore 2-(naphthalen-1-yl)-1-((naphthalen-1-yl)methyl)-1H-benzimidazole (NNMB) has been prepared and characterized by (1)H NMR, (13)C NMR, mass and IR spectral analysis. Absorption, fluorescence and synchronous fluorescence spectral studies have been made for the mutual interaction of NNMB with bovine serum albumin (BSA). Absorption spectroscopy proved the formation of a ground state BSA…NNMB complex. Fluorescence spectrum of BSA in the presence of NNMB clearly shows that NNMB acts as a quencher. Based on the theory of Foresters non-radiation energy transfer (FRET) binding distance has been deduced. The Stern-Volmer quenching constant (KSV), binding site number (n), apparent binding constant (KA) and corresponding thermodynamic parameters (ΔG, ΔH and ΔS) were determined.

Highly phosphorescent green emitting iridium(III) complexes for application in OLEDs

Phenanthrimidazole based ligands with various substitution patterns have been used as the main ligands for heteroleptic bis-cyclometalated iridium(III) complexes. Two series of complexes have been prepared by changing the ancillary ligand and their electroluminescent properties were studied. The strongly allowed phosphorescence in these complexes is the result of a significant spin–orbit coupling of the iridium center. The absorption at longer wavelengths has been assigned to 1MLCT ← S0 and 3MLCT ← S0 transitions of iridium complexes and the phosphorescence emission maxima range from 558 to 574 nm. The OLEDs with these picolinate complexes exhibit appreciable external quantum efficiencies ranging from 6.5 to 15.6%. Devices based on Ir(tmpmp)2(pic) and Ir(tmpdp)2(pic) show better performance in terms of brightness of 110 421 cd m−2 and 124 568 cd m−2 at 18 V, respectively. Devices with Ir(tmpdp)2(pic) show a high power efficiency of 25.6 lm W−1 at 7.0 V and a current efficiency of 47.5 cd A−1 at 8.0 V. Introduction of the dimethylamino group in 2-picolinate complexes, Ir(tmpmp)2(Npic) (ηc − 44.6 cd A−1, 8 V; ηp − 26.0 lm W−1, 7 V) and Ir(mpdp)2(Npic) (ηc − 49.9 cd A−1, 8 V; ηp − 27.2 lm W−1, 7 V), results in a highly phosphorescent green emitter with high electroluminescence efficiency.

Interaction of fluorescent sensor with superparamagnetic iron oxide nanoparticles.

To sense superparamagnetic iron oxides (Fe2O3 and Fe3O4) nanocrystals a sensitive bioactive phenanthroimidazole based fluorescent molecule, 2-(4-fluorophenyl)-1-phenyl-1H-phenanthro [9,10-d] imidazole has been designed and synthesized. Electronic spectral studies show that phenanthroimidazole is bound to the surface of iron oxide semiconductors. Fluorescent enhancement has been explained on the basis of photo-induced electron transfer (PET) mechanism and apparent binding constants have been deduced. Binding of phenanthroimidazole with iron oxide nanoparticles lowers the HOMO and LUMO energy levels of phenanthroimidazole molecule. Chemical affinity between the nitrogen atom of the phenanthroimidazole and Fe(2+) and Fe(3+) ions on the surface of the nano-oxide may result in strong binding of the phenanthroimidazole derivative with the nanoparticles. The electron injection from the photoexcited phenanthroimidazole to the iron oxides conduction band explains the enhanced fluorescence.

Physico-chemical studies of fused phenanthrimidazole derivative as sensitive NLO material.

Heterocyclic phenanthrimidazole derivative, 2-(4-fluorophenyl)-1-p-tolyl-1H-imidazo[4,5-f] [1,10] phenanthroline (FPTIP) has been synthesized and characterised by NMR, mass and CHN analysis. The FPTIP was evaluated concerning their solvatochromic properties and molecular optical nonlinearities. Their electric dipole moment (μ), polarizability (α) and hyperpolarizability (β) have been calculated theoretically and the results indicate that the extension of the π-framework of the ligands has an effect on the NLO properties. The energies of the HOMO and LUMO levels and the molecular electrostatic potential (MEP) energy surface studies have exploited the existence of intramolecular charge transfer (ICT) within the molecule.

Excited Charge Transfer States in Donor–Acceptor Fluorescent Phenanthroimidazole Derivatives

Solvent-dependent electronic structure of the selected donor (D) acceptor (A) derivatives of phenanthroimidazole derivatives containing fluoro substituent as an electron acceptor fragment in the fluorescent charge transfer (CT) states has been investigated. The mechanism of the radiative charge recombination CT → S0 is discussed in terms of the Mulliken–Murrell model of the CT complexes and the Marcus theory of photoinduced electron transfer (ET). Solvatochromic effects on the spectral position and profile of the stationary fluorescence spectra clearly indicate the CT character of the emitting singlet states of all of the compounds studied both in a polar and a non polar environment. An analysis of the CT fluorescence leads to the quantities relevant for the electron transfer in the Marcus inverted region. The values of the fluorescence rate constants (kr) and corresponding transition dipole moments (M) and their solvent polarity dependence indicate that the electronic coupling between the emitting 1CT state and the ground state is a governing factor of the radiative transitions. The relatively large values of M indicate a nonorthogonal geometry of the donor and acceptor subunits in the fluorescent states. It is shown that Marcus theory can be applied for the quantitative description of the radiationless charge recombination processes in the cases when an intersystem crossing to the excited triplet states can be neglected.

Contrasting emission behaviour of phenanthroimidazole with ZnO nanoparticles.

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.

1-(4-Methoxyphenyl)-2-[4-(trifluoromethyl)phenyl]-1H-phenanthro[9,10-d]imidazole

In the title compound, C29H19F3N2, the tetracyclic 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 methylphenyl and fluorophenyl rings, respectively. An intramolecular C—H⋯π interaction occurs. In the crystal, pairs of C—H⋯π interactions link inversion-related molecules.