Excitation Wavelength Dependence Study Research Articles

Fluorescence Resonance Energy Transfer in Microemulsions Composed of Tripled-Chain Surface Active Ionic Liquids, RTILs, and Biological Solvent: An Excitation Wavelength Dependence Study

In this article we have reported the fluorescence resonance energy transfer (FRET) study in our earlier characterized surface active ionic liquids (SAILs)-containing microemulsion, i.e., N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([P13][Tf2N])/[CTA][AOT]/isopropyl myristate ([IPM]) and N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide ([N3111][Tf2N])/[CTA][AOT]/[IPM] microemulsions (Banerjee, C.; Mandal, S.; Ghosh, S.; Kuchlyan, J.; Kundu, N.; Sarkar, N. J. Phys. Chem. B 2013, 117, 3927-3934). The occurrence of effective FRET from the donor, coumarin-153 (C-153) to the acceptor rhodamine 6G (R6G) is evident from the decrease in the steady state fluorescence intensity of the donor with addition of acceptor and subsequent increase in the fluorescence intensity of the acceptor in the presence of donor. The excitation wavelength dependent FRET from C-153 to R6G has also been performed to assess the dynamic heterogeneity of these confined systems. In time-resolved experiments, the significant rise time of the acceptor in the presence of the donor further confirms the occurrence of FRET. The multiple donor-acceptor (D-A) distances, for various microemulsions, obtained from the rise times of the acceptor emission in the presence of a donor can be rationalized from the varying distribution of the donor, C-153, in the different regions of the microemulsion. Time-resolved measurement reveals that with increasing excitation wavelength from 408 to 440 nm, the contribution of the faster rise component of FRET increases significantly due to the close proximity of the C-153 and R6G in the polar region of the microemulsion where occurrence of FRET is very high. Moreover, we have also studied the FRET with variation of R (R = [room temperature ionic liquids (RTILs)]/[surfactant]) and shown that the effect of excitation wavelength on FRET is similar irrespective of R values.

Effect of the Alkyl Chain Length on the Rotational Dynamics of Nonpolar and Dipolar Solutes in a Series of N-Alkyl-N-Methylmorpholinium Ionic Liquids

Rotational dynamics of two dipolar solutes, 4-aminophthalimide (AP) and 6-propionyl-2-dimethylaminonaphthalene (PRODAN), and a nonpolar solute, anthracene, have been studied in N-alkyl-N-methylmorpholinium (alkyl = ethyl, butyl, hexyl, and octyl) bis(trifluoromethansulfonyl)imide (Tf2N) ionic liquids as a function of temperature and excitation wavelength to probe the microheterogeneous nature of these ionic liquids, which are recently reported to be more structured than the imidazolium ionic liquids (Khara and Samanta, J. Phys. Chem. B2012, 116, 13430-13438). Analysis of the measured rotational time constants of the solutes in terms of the Stokes-Einstein-Debye (SED) hydrodynamic theory reveals that with increase in the alkyl chain length attached to the cationic component of the ionic liquids, AP shows stick to superstick behavior, PRODAN rotation lies between stick and slip boundary conditions, whereas anthracene exhibits slip to sub slip behavior. The contrasting rotational dynamics of these probe molecules is a reflection of their location in distinct environments of the ionic liquids thus demonstrating the heterogeneity of these ionic liquids. The microheterogeneity of these media, in particular, those with the long alkyl chain, is further evidence from the excitation wavelength dependence study of the rotational diffusion of the dipolar probe molecules.

Solvation and rotational relaxation of coumarin 153 in a new hydrophobic ionic liquid: An excitation wavelength dependence study

The solvent relaxation and rotational dynamics of coumarin 153 have been investigated in a new room temperature ionic liquid, 1-(2-methoxyethyl)-1-methylpyrrolidiniumtris(pentafluorethyl)trifluorophosphate [[MOEMPL][FAP]], at three different excitation wavelengths with a variation in temperature. Wavelength -dependent fluorescence decay behavior of the probe molecule in the present medium has been investigated by studying the time dependent fluorescence Stokes shift in the ps–ns time scale. The dynamic fluorescence Stokes shift measurements suggest that the time-resolvable part of the solvation dynamics is biphasic in nature and the average solvation time depends on the excitation wavelengths. Rotational coupling constants, obtained from the time- resolved anisotropy data, indicate no specific interaction between the probe molecule and the ionic liquids. The excitation wavelength dependent solvation dynamics is attributed to the heterogeneous nature of the present ionic liquid.

Dual Intramolecular Hydrogen Bond as a Switch for Inducing Ground and Excited State Intramolecular Double Proton Transfer in Doxorubicin: An Excitation Wavelength Dependence Study

This paper investigates how solution conditions, especially solvent polarity and hydrogen bonding, influence the fluorescence of an anticancer drug, doxorubicin hydrochloride (DOX). When excited at 480 nm, this molecule shows single fluorescence. However, when excited at 346 nm, it shows dual fluorescence. The ground and excited state intramolecular double proton transfer in DOX has been observed and investigated to shed light on their corresponding spectroscopy and dynamics in different protic and aprotic solvents. An increase in pH results in enhancement of emission from the ionic conformer with parallel dwindling of emission of the neutral species. Based on the experimental and theoretical studies on DOX, a ground and excited state intramolecular double proton transfer mechanism is proposed to explain the unusual excitation-dependent dual fluorescence of DOX.

Ultraviolet resonance Raman spectroscopy as a robust spectroscopic tool for in situ sunscreen analysis

Current techniques being used for sunscreen analysis are incapable of direct determination of the active ingredients in sunscreen formulations. Therefore, the development of methodologies for rapid in situ analysis of sunscreens is desirable. This paper describes the application of ultraviolet resonance Raman spectroscopy (UVRRS) to the direct in situ analysis of sunscreen formulations. High-quality UV resonance Raman spectra were obtained for five sunscreen active ingredients (AIs), mixtures of the AIs and real sunscreen formulation samples. The spectra from the sunscreen formulations gave distinct spectral signatures indicative of the sunscreen AIs in each sample, with essentially no interference from the complex sunscreen matrix. Also, despite the fact that many of the AIs are fluorescent, no fluorescence interferences in the resonance Raman spectra were observed. Excitation wavelength-dependent studies throughout the 244–275 nm region demonstrate that the best discrimination of the AIs was achieved at an excitation wavelength of 244 nm. Thus, by tuning the excitation wavelength within the absorption bands of the AIs, complete identification of these analytes can be achieved in situ without any sample pretreatment or separation. The limit of detection found for a common AI in situ with this technique is 0.23% (w/w), the limit of quantitation is 0.78% (w/w), while the dynamic range is between 0.8% and 50% (w/w). The technique is fast, robust, lacks any major interference, and can be adapted for routine online quality control.

Bonding configurations in amorphous carbon and nitrogenated carbon films synthesised by femtosecond laser deposition

The effect of nitrogen addition and laser fluence on the atomic structure of amorphous carbon films (a-C) synthesized by femtosecond pulsed laser deposition has been studied. The chemical bonding in the films was investigated by means of X-ray photoelectron (XPS) and Raman spectroscopies. XPS studies revealed a decrease in the sp3 bonded carbon sites and an associated increase in the N-sp2C bonding sites with increasing nitrogen content in the CNx films. An increase in laser fluence from 0.36 to 1.7 J/cm2 led to a rise in sp3C sites. These results were further confirmed by Raman spectroscopy. The ID/IG ratio increased monotonically and G line-width decreased with the increase of nitrogen content in the films indicating a rise in either the number or the size of the sp2 clusters. Furthermore a visible excitation wavelength dependence study established the resonant Raman process in a-C and CNx films.