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Steady‐State and Time‐Resolved Emission Studies of 6‐Methoxy Quinoline

Abstract Steady‐state absorption, fluorescence excitation, and emission spectra of 6‐methoxy quinoline (6‐MQ) were measured at room temperature in cyclohexane, dioxane, ethanol, acetonitrile, water, and water–dioxane solvents. Absorption spectra of cyclohexane, n‐hexane, and isopentane solutions show resolved vibronic structure at room temperature. However, the excitation spectrum of cyclohexane solution is structureless and is found to be emission wavelength dependent, indicating the formation of at least two distinct species in the ground state. Similar behavior was observed in dioxane and water–dioxane solutions. For all other solutions, the fluorescence excitation spectrum of 6‐MQ was found to be the same for different emissions. Emission of 6‐MQ in all solvents consisted of two bands with their maxima around 355 nm (I) and 430 nm (II), the actual positions and the relative intensities being dependent on the solvent used. The bands I and II were respectively attributed to normal and protonated/H‐bonded species of either 1La or 1Lb states or mixed (1La/1Lb) state of ππ* character. Fluorescence decay of this dye in all solvents monitored over each emission maximum showed biexponential behavior, and the analysis yielded two different lifetime components for each emission band. The short and long fluorescence decay components were respectively in the range of 0.30–3.00 ns and 18–20 ns. The observed emission characteristics coupled with the nature of the fluorescence polarization spectra and two different decay components for each emission suggest the existence of two different conformers having two different excited electronic states.

Picosecond time-resolved laser emission of coumarin 102: Solvent relaxation

The time-resolved laser emission of coumarin 102 was investigated in various aprotic and protic solvents at picosecond resolution by frequency upconversion technique. The spectral shift of the transient emission spectrum is attributed to solvent reorientation and the results are discussed.

Spectroscopic study of rotational energy distribution of BH (A 1Π) and electronic excitation temperature determination

Emission spectra of BH(A1Π-X1Σ+) system were recorded and studied using a low pressure (3.0 torr) arc in flowing hydrogen and argon + hydrogen mixture. The rotational distributions in theA1Π state determined from the intensities of rotational lines for the 0–0 band of theA-X system conforms to a Maxwellian distribution with effective rotational temperature of 1000 ± 50°K. Intensities of Balmer lines of hydrogen were measured and used to determine electronic excitation temperature which was found to be around 2000°K.

Orientational Relaxation of Aminocoumarins by Time Resolved Dichroism with Picosecond Pulses

Abstract The orientational relaxation times (τr) of coumarin 102 and coumarin 138 molecules were measured in ethanol and ethylene glycol solutions at room temperature by transient dichroism technique on picosecond time scales. The experimental data were compared with the calculated values based on Stokes-Einstein-Debye (SED) hydrodynamic model. The results show that the measured values of τr of both the dyes in ethanol reasonally agree with the theoretical ones; but for ethylene glycol solutions, relaxation times are shortened indicating the inadequacy of the SED model for the description of the rotational motions. The results are discussed on the basis of molecular structures of the dyes and intermolecular interactions.

Fluorescence and Laser Emission from Coumarin-Acridine Orange Mixtures

Abstract The sensitized fluorescence and laser emissions of dye mixtures; (I) coumarin 102 (donor) and acridine orange (acceptor) and (II) coumarin 47 (donor) and acridine orange (acceptor) with Hg-lamp and N2 laser, have been measured as a function of dye concentration and of the pump power (N2 laser). Acridine orange which does not lase by itself on excitation with N2 laser, lases efficiently in the presence of 7-amino-coumarins via singlet-singlet energy transfer. Energy transfer rate constants and critical distances have been estimated from fluorescence intensity and lifetime measurements. The performance of energy transfer dye lasers (ETDLs) are discussed in terms of spectral characteristics of the dyes and their penetration depths.

Intermolecular energy transfer in mixed laser dyes: photophysical properties of triplet states

Triplet-singlet energy transfer in laser dyes have been studied in EPA at 77K using N2 laser as an excitation source. Phosphorescence of the donor (D) and the delayed fluorescence of the acceptor (A) and their lifetimes have been measured for coumarin 102 (D)-rhodamine B(A) and 9(10H)-acridone (D)-rhodamine 6G(A) dye systems as a function of acceptor concentration. These data yield energy transfer rate constants of ∼103 dm3 mol−1 s−1 for the donor acceptor combinations, consistent with the Forster mechanism. The phosphorescence quantum efficiency and other spectral parameters are also reported.

Ground-state recovery of coumarin dyes by pump-probe technique with picosecond pulses

Rotation-free transmission measurements governed by ground-state recovery of coumarin 102, coumarin 138 and coumarin 339 dyes in ethanol solutions were performed for the first time by pump-probe technique using 35 ps pulses of Nd:YAG laser at 355 nm. Recovery of absorption is characterized by simple exponential behaviour with relaxation times of 4.0, 3.7 and 3.0 ns respectively for C 102, C 138 and C 339. These values are comparable to the lifetimes of the first excited singlet states.

Laser induced long-lived emission spectra of laser dyes in rigid glasses at 77 K

Phosphorescence decay of 3-(2′-N-methylbenzimidazolyl)-7-N, N-diethylaminocoumarin; 2,3,5,6-1H, 4H-tetrahydro-8-methylquinolizino-〈9, 9a, 1-gh〉 coumarin; 2,3,5,6-1H, 4H-tetrahydro-8-trifluormethylquinolizino-〈9,9a,1-gh〉 coumarin; 9(10H)-acridone; 9-aminocridine hydrochloride, 1-hydrate and 2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3, 4-oxadiazole dyes in EPA glass at 77 K have been recorded using N2 laser. The results were used to determine lifetimes. Emission intensities from the first two dyes have been examined in relation to dye concentration and excitation intensity. The results are discussed.

Successive approximation to determine rotational temperature

A method using successive approximation is developed for determining the rotational temperatures, when the rotational lines are overlapped. The method is applied to CH (B2Σ− −X2 II) band as a test.