Basudeb Haldar

Photophysics of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine: emission from two states

Steady state photophysics of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ) has been studied in different pure and mixed solvents. The fluorometric behaviour of AODIQ is modified dramatically with a change in the solvent polarity. The fluorescence quantum yield, when plotted against the solvent polarity parameter (E T (30)), passes through a maximum. Plot of the fluorescence parameters in a graded series of dioxane-water mixture against E T (30) shows segmented linearity with two independent slopes; reflecting a lower sensitivity in the less polar region and a much higher sensitivity in higher polarity range. The observations lead to the proposition that the fluorescence of AODIQ originates from two different states, viz., a locally excited (LE) and a charge transfer (CT) one. Studies of the phosphorescence and heavy atom quenching of the fluorescence reveal that the CT state lies above the lowest triplet state even in a very polar environment.

Effect of nanocavity confinement on the rotational relaxation dynamics : 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine in micelles

In continuation of our recent study on the steady state photophysics of a biologically active beta-carboline derivative, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), in the present article we have investigated the effect of nanocavity confinement on the excited state dynamics and rotational relaxation of the probe using picosecond time resolved fluorescence and fluorescence anisotropy techniques. The polarity dependent intramolecular charge transfer process is responsible for the remarkable sensitivity of this biological fluorophore in micellar environments. The fluorescence anisotropy decay of AODIQ incorporated inside the micelle is biexponential. The rotational motion of the probe was interpreted on the basis of a two step model consisting of a fast restricted rotation of the probe and a slow lateral diffusion of the probe in the micelle; both coupled to the overall rotation of the micelle. Experimental results reveal that micellar environment causes significant retardation of both the wobbling as well as the translational motion of the probe.

A Strategic Design of an Opto-Chemical Security Device with Resettable and Reconfigurable Password Based Upon Dual Channel Two-in-One Chemosensor Molecule

A simple strategy is proposed to design and develop an intelligent device based on dual channel ion responsive spectral properties of a commercially available molecule, harmine (HM). The system can process different sets of opto-chemical inputs generating different patterns as fluorescence outputs at specific wavelengths which can provide an additional level of protection exploiting both password and pattern recognitions. The proposed system could have the potential to come up with highly secured combinatorial locks at the molecular level that could pose valuable real time and on-site applications for user authentication.

Photophysical, NMR and density functional study on the ion interaction of norharmane: proton transfer vs. hydrogen bonding

Interactions of norharmane (S), with different ions have been studied using spectroscopy, NMR and density functional studies. A significant gradual change both in absorption and emission spectra was observed upon addition of fluoride anions. The spectral change in the absorption and emission bands of norharmane (S) is found to be specific to fluoride ion; it is unaffected by the presence of other ions. Hydrogen bond mediated proton transfer from norharmane to fluoride is mainly attributed to the fluoride selective signaling behavior. Calculations of the transition energies of the norharmane (S), anionic species of norharmane (S−) and hydrogen bonded complexes (S⋯F−) show that the added fluoride anion could capture the proton in the free N–H moiety instead of the hydrogen-bonding one. Experimental results reveal that the long-wavelength absorption band in the presence of fluoride ion is due to the formation of anion.

Binding interaction of a newly developed bisindole drug molecule with α-cyclodextrin: face to face shielding of indole hoops

Binding interactions of a newly developed drug molecule namely 3,3′-bis(indolyl)-4-chlorophenylmethane (BICPM) with α-cyclodextrin have been studied using steady state and picosecond time resolved fluorometric techniques. A significant increase both in steady state anisotropy (r) and in the average rotational correlation time in the CD environments compared with that in a pure aqueous phase indicates that the rotational dynamics of BICPM are substantially slowed down upon binding with the α-cyclodextrin. Critical spectral analysis reveals the formation of two types of inclusion complex between the fluorophore and α-cyclodextrin (α-CD) depending on the relative population of the two. The stoichiometries and association constants of these complexes have been determined by monitoring the fluorescence data. Hydrodynamic radii of the formed 1 : 2 probe-α-cyclodextrin supramolecular complex have also been determined. From the determined hydrodynamic radii and from molecular docking analysis it is argued that probably two CD cavity shields the indole moiety in a face-to-face manner.