Periyasamy Ramanathan

Efficient hole transport materials based on novel fused methoxynaphthyl phenanthrimidazole core structure were synthesised and characterized. Their device performances in phosphorescent organic light emitting diodes were investigated. The high thermal stability in combination with the reversible oxidation process made promising candidates as hole-transporting materials for organic light-emitting devices. Highly efficient Alq₃-based organic light emitting devices have been developed using phenanthrimidazoles 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.

Understanding the interaction between the nanomaterials and bioactive molecules are of current interest due to the potential application of nanomaterial in biomedical field. The structural, electronic and optical properties of newly synthesised fluorophore 2-(4-methoxynaphthalen-1-yl)-1-phenyl-1H-phenanthro[9.10-d]imidazole have been investigated in detail. The imidazole absorbs strongly on the surface of TiO₂ nanocrystals probably because of the chemical affinity of azomethine nitrogen atom of the imidazole, resulting in lowering the HOMO and LUMO energy levels. The TEM, SEM and EDX spectra confirm the adsorption of imidazole on the surface of TiO₂ nanocrystals. The growth behavior and stability of small stoichiometric (TiO₂)_n clusters have been analysed by using density functional theory which reveals that clusters prefers three-dimensional structures. In addition, the interaction between the ground state structure of the (TiO₂)_n cluster and a single imidazole molecule have been studied. The calculated binding energy (E_b) and the energy gap (E_g) indicate that the imidazole molecule preferably binds to the Ti atom of the (TiO₂)_n clusters through its azomethine nitrogen atom; the binding energy is in range 5.24–7.89 eV. In order to understand the binding interaction with DNA docking study has been carried out.

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.

Catalytic synthesis of some polysubstituted imidazoles under solvent-free condition is reported and their characterization has been carried out spectral techniques. Electronic spectral studies reveal that their solvatochromic behavior depends both the polarity of the medium and 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 absorption and emission spectral results has 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 imidazoles fit satisfactorily to a bi exponential kinetics. These observations are in consistent with quantum chemical calculations.

The dynamics of photoinduced electron injection from (E)-1-(4-methoxyphenyl)-2-styryl-1H-phenanthro [9,10-d]imidazole (MPSPI) synthesised using nano TiO₂ as catalyst to Fe₂O₃ nanocrystal has been studied by FT-IR, absorption, fluorescence and lifetime spectroscopic methods. The binding between nanoparticle and MPSPI is confirmed by binding constant and binding site. The distance between MPSPI and nanoparticle as well as the critical energy transfer distance has been obtained. The free energy change (ΔG_et) for electron injection has also been deduced.