K.I. Priyadarsini

Nonradiative energy transfer from 7-amino coumarin dyes to thiazine dyes in methanolic solutions

Abstract Nonradiative energy-transfer processes between 7-amino coumarin and thiazine dyes in methanolic solutions have been studied using a single-photon counting technique. The critical transfer distances calculated from the experimantal rate constants are in the range 30–70 A and exhibit the same trend as the values calculated from Forsters formula.

A study of the triplet state of 7-amino coumarin laser dyes by the nanosecond pulse radiolysis technique

Abstract The triplet characteristics of two 7-amino coumarin laser dyes (7-diethylamino 4-methyl coumarin (C 1) and 7-diethylamino 4-trifluoromethyl coumarin (C 1F)) were studied in benzene solution using the nanosecond pulse radiolysis technique. Their T—T absorption spectra, rate constants for triplet to ground state transition and triplet—triplet annihilation and G values were determined. The energy transfers from coumarin triplets to various acceptor molecules such as pyrene, t -stilbene and anthracene and from benzene, biphenyl and naphthalene triplets to these dyes as acceptors were studied. Estimates of their energy levels were made.

Triplet state of coumarin 153 studied by nanosecond pulse radiolysis

Abstract The triplet—triplet absorption spectrum of the rigidized 7-amino coumarin dye C 153 has been investigatd in benzene solution in the region 450 – 750 nm by the pulse radiolysis technique. The triplet decay was first order with a half-life of 5 μs. Its formation was confirmed by energy transfer from the pulse radiolytically generated biphenyl triplet. The extinction coefficient of C 153 triplet in benzene was calculated to be 10 000 ± 500 dm 3 mol −1 cm −1 . Using various triplet donors and acceptors its energy level was estimated to be 50 ± 2 kcal mol −1 . The energy transfer rate constants from benzene, biphenyl and naphthalene triplets to C 153 and from C 153 triplet to anthracene were found to be diffusion controlled.

Studies of the triplet state of coumarin 102 laser dye by pulse radiolysis

Abstract The absorption spectrum of the triplet state of the laser dye coumarin 102 (C 102) has been recorded in benzene solution employing the pulse radiolysis technique. Triplet formation was confirmed and its extinction coefficient determined by energy transfer from known triplet sensitizers. The triplet energy of C 102 has been estimated to be 57.5±1.5 kcal mol −1 . Properties of the C 102 triplet are compared with those of its trifluoro analogue coumarin 153 (C 153).

Photophysical studies on charge transfer complexes of γ-cyclodextrin-C60 with electron-rich amines and sulphur compounds

Abstract The formation of donor-acceptor complexes of γ-cyclodextrin-C60-γ-cyclodextrin (CDC60CD) with electron-rich amines and sulphur compounds was studied in aqueous solution. The stoichiometry, equilibrium constants and extinction coefficients of the charge transfer complexes were determined by steady state absorption measurements. Picosecond time-resolved studies on CDC60CD showed the formation of C60 triplets, which were found to decrease with increasing concentration of 1,4,-diazabicyclo[2.2.2]octane (DABCO).

Preparation and characterization of DABCOδ+x-Cδ−60(y) charge transfer complex

Abstract A stable complex of C 60 with an organic donor (tertiary amine, DABCO) has been prepared in the solid state at room temperature. The charge transfer complex, DABCO δ+ x -C δ− 60( y ) is characterised by powder X-ray diffraction and FTIR methods. The complex is soluble in an aqueous medium and shows weak paramagnetic properties.

Effect of 1,4-diazabicyclo-[2,2,2]-octane on the laser properties of 7-amino coumarin dyes

1,4-Diazabicyclo-[2,2,2]-octane (Dabco), a tertiary amine, was found to quench the fluorescence of two 7-amino coumarin dyes C1 and C102. The quenching was monitored in solvents of varying polarity. In non-polar and polar aprotic solvents the quenching is very efficient and the rate constants for quenching are within diffusion-controlled limits, whereas in protic solvents the quenching efficiency is very low. An attempt has also been made to delineate the mechanism for the stabilization of a dye laser by Dabco, following the reactions of the triplets of C1 with Dabco and also by monitoring the photodegradation of C1 in the presence of Dabco.

Direct energy transfer in charged micellar systems : a model

Abstract In the present paper, the non-radiative energy transfer between the donor coumarin 102 and the acceptor rhodamine 6G was studied in order to investitage Forsters mechanism when the donor is locked inside the micelle of cetyl trimethyl ammonium bromide and the acceptor is distributed in the electrical double layer. The Forster radius and the micellar charge are evaluated.

Nanosecond pulse radiolysis studies on coumarin 153 in cyclohexane solutions

Abstract In the pulse radiolysis of oxygen-free cyclohexane solutions of the laser dye coumarin 153, two light-absorbing transient species have been observed, attributable to the solute radical cation (λ m ≈ 450 nm) and the triplet (broad, 500–700 nm). The latter was confirmed by energy transfer from pulse radiolytically generated biphenyl triplet.

Comparative triplet studies of 7-amino 4-methyl coumarin laser dye in nafion membranes and in homogeneous solutions

Abstract The triplets of 7-amino 4-methyl coumarin (Cl 20 ), a laser dye, were studied in benzene as well as in a polymeric membrane, (Nafion-117). The triplet lifetimes and TT absorption spectra were determined. The TT energy transfer studies between biphenyl—C120 and C120—thionine were carried out in the membrane and the results compared with those obtained in benzene. Due to very slow diffusion of the dye, the energy transfer rates are very low and they are not very efficient compared with other deactivation processes. Effect of counter-ion on the fluorescence lifetimes and triplet yields were studied to see heavy atom effect inside the nafion membrane.