Picosecond Emission Spectroscopy Research Articles

Synthesis and comparative study of the photocatalytic performance of hierarchically porous polymeric carbon nitrides

Graphitic carbon nitride materials with tri-s-triazine and s-triazine based structures were prepared by thermal condensation of melamine (CNT) and by solution reaction of cyanuric chloride with lithium nitride (CNS), respectively. An amphiphilic block copolymer-F68 was used as a soft template for the synthesis of mesoporous carbon nitride. The structural and photophysical properties of the as-prepared catalysts were characterized by X-ray powder diffraction, elemental analysis, N2-adsorption measurement, transmission electron microscopy, X-ray photoelectron spectroscopy, differential scanning calorimeter and UV–Vis absorption as well as time-resolved picosecond emission spectroscopy. The photocatalytic activity of the samples was evaluated by H2 evolution from water under visible light irradiation and the degradation of rose bengal (RB). The mesoporous CNT materials prepared with Pluronic F68 as template showed markedly higher activity compared to bulk carbon nitride, which can be attributed to its crystallinity, hierarchical porous structure and the enlarged surface area. The catalyst was relatively stable as proven by recycling experiments. Besides, the addition of H2O2 promoted the formation of active ·OH radicals and increased the activity of carbon nitride for photodegradation of rose bengal. The carbon nitrides prepared by solution reactions were of very poor activity both in photocatalytic water splitting and rose bengal degradation.

Study of rotational dynamics of receptor-targeted contrast agents in cancerous and normal prostate tissues using time-resolved picosecond emission spectroscopy

We studied the time-resolved polarization-dependent fluorescence spectroscopy of receptor-targeted contrast agents (Cybesin and Cytate) bound with prostate cancer cells in prostate tissue. An analytical model dealing with highly viscous tissue media was developed and used to investigate the rotation times and fluorescence anisotropies of the receptor-targeted contrast agents in prostate tissue. The differences of rotation times and fluorescence anisotropies were observed for Cybesin (Cytate) in cancerous and normal prostate tissues, which reflect changes of the microstructures of cancerous and normal tissues and their different bound affinity with contrast agents. The preferential uptake of Cytate (Cybesin) in cancerous tissue was used to image and distinguish cancerous tissue areas from normal tissue areas. The fluorescence polarization difference imaging technique was used to enhance the image contrast between the cancerous and normal tissue areas. This research may help to introduce a new optical approach and criteria for prostate cancer detection.

Study of protein–surfactant interaction using excited state proton transfer

Abstract Excited state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulfonate) is studied in a lysozyme–cetyltrimethylammonium bromide (CTAB) complex using picosecond emission spectroscopy. The critical association concentration (CAC) of CTAB is found to be ∼0.4 mM. Using a kinetic analysis it is shown that deprotonation, recombination and dissociation of the geminate ion pair in the lysozyme–CTAB aggregate are faster than that in a CTAB micelle.

Solvation Dynamics of DCM in Dipalmitoyl Phosphatidylcholine Lipid

Solvation dynamics of 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl) 4H-pyran (DCM) in dipalmitoylphosphatidylcholine (DPPC) vesicles in water is studied using picosecond emission spectroscopy. The solvation dynamics of DCM in DPPC vesicles is found to be bi-exponential with two components of 120±20ps (20%) and 5.5±0.5ns (80%). This indicates slow relaxation of the water molecules inside the water pool of the lipid vesicles.

Photoisomerisation of diethyloxadicarbocyanine iodide in micelles

Photoisomerisation of 3,3′-diethyloxadicarbocyanine iodide (DODCI) is studied in cationic (cetyl trimethyl ammonium bromide, CTAB), anionic (sodium dodecyl sulfate, SDS) and neutral (triton X-100, TX) micelles using picosecond emission spectroscopy. On addition of the surfactants to an aqueous solution of DODCI, above the critical micellar concentration, the emission quantum yield and lifetime of DODCI increase due to a marked decrease in the photoisomerisation rate. The retardation of the photoisomerisation process, is attributed to the high microviscosity at the micellar interface, compared to bulk water. Assuming that the Smoluchowski limit and the same `slip'/`stick' boundary condition hold for all three micelles, the effective microviscosities of the CTAB, SDS and TX micelles are estimated to be 70.0±20, 24.5±2 and 26.0±2 cP, respectively.

Intramolecular Charge Transfer near a Hydrophobic Surface. 2,6-p-Toluidinonaphthalene Sulfonate in a Reverse Micelle

Intramolecular charge transfer (ICT) processes of 2,6-p-toluidinonaphthalene sulfonate (TNS) in the water pool of sodium dioctyl sulfosuccinate (AOT) reverse micelle in heptane, is studied using picosecond emission spectroscopy. It is observed that while in aqueous solutions the lifetime (τf) of TNS is 80 ps, τf increases to 4 ns in the microemulsion with water to AOT ratio, w0=4. With increase in w0 as the water pool swells in size, the lifetime and quantum yield of emission decrease and the rate of the ICT process increases. However, the magnitude of the change (at most ≈70 times at w0=4) in the rate of the ICT process of TNS compared to ordinary water is smaller than the several thousand fold retardation in the solvation dynamics of water in such a water pool relative to bulk water. This is attributed to the fact that while the solvation dynamics in the water pool is governed by the dielectric relaxation, dynamics of the ICT process is controlled by the static polarity of the medium.

Intramolecular Charge Transfer Processes in Confined Systems. Nile Red in Reverse Micelles†

Intramolecular charge transfer (ICT) processes of the neutral fluorescence probe, nile red, I, confined in the water pool of aerosol-OT (AOT) reverse micelle in n-heptane, is studied using picosecond emission spectroscopy. Utilizing the solvatochromism of nile red, only those probe molecules inside the reverse micelle are selectively excited. It is observed that while in aqueous solutions the lifetime (τf) of nile red is 650 ps, inside the reverse micelles τf increases to 3.73 ns in reverse micelle and to 2.06 ns at the highest water content of the microemulsion (wo = 32). With increase in the water-to-surfactant ratio, wo, as the water pool swells in size, the lifetime and quantum yield of emission decrease and the rate of the ICT process of nile red increases. However, the magnitude of the change (at most 8 times) in the rate of the ICT process of nile red compared to that of ordinary water is much smaller than the several thousandfold decrease observed in the solvation dynamics of water in the water po...

NEW FEATURES IN THE PHOTOPHYSICS and PHOTOCHEMISTRY OF 2‐(2'‐HYDROXY‐PHENYL)BENZOTHIAZOLES INTRODUCED BY AMINE SUBSTITUTION

The photophysics and photochemistry of the 4'-diethylamino derivative of both 2-phenyl-benzothiazole and 2-(2'-hydroxyphenyl)benzothiazole have been studied by nanosecond and microsecond laser flash photolysis and picosecond emission spectroscopy. For the non-hydroxy substituted molecule, the singlet excited state was shown to relax primarily via fluorescence emission, and a very weak triplet transient was observed after laser flash excitation. The 2-(2'-hydroxy-4'-diethylaminophenyl)benzothiazole (AHBT) was shown to undergo excited state intramolecular proton transfer (ESIPT) in the picosecond timescale (k greater than 3 x 10(10) s-1) to form a colored zwitter-ion/keto form in solution at room temperature while the ground state back proton transfer was slower by a factor of approximately 10(5). However, in marked contrast with other derivatives of 2-(2'-hydroxyphenyl)benzothiazole and related molecules, the ESIPT was not the only deactivation process of the lowest singlet excited state of the enol form. Under steady-state excitation at room temperature (and low temperature), the fluorescence emission of the enol form was observed. The T-T absorption of the enol form was also observed and furthermore, the ESIPT was shown to have an activation energy which was estimated to be approximately 4 kJ. None of the foregoing, fluorescence and T-T absorption of the enol nor activation energy for proton transfer have been observed for the parent or derivatives of 2-(2'-hydroxyphenyl)benzothiazoles. The striking new features for the ESIPT photochemistry and photophysics for the 4'-diethylamino derivative of 2-(2'-hydroxyphenyl)benzothiazole are discussed and MO calculations are used to aid in the interpretation of some of the experimental results.

Effect of viscosity and rotor size on the dynamics of twisted intramolecular charge transfer

Picosecond emission spectroscopy is used to examine the kinetics of twisted intramolecular charge transfer in a series of symmetric bis ((N,N-dialkylamino)phenyl) sulfones, DRAPS (R=methyl, propyl, and butyl), in alcohol solutions. Within a given solvent, the dynamics of charge transfer are not dependent on changes in the size of the rotating group; however, for a single molecule in the series of n-alcohols, the rate of charge transfer correlates with the inverse of the solvent viscosity

Nonequilibrium and nonadiabatic effects on excited state electron transfer reactions in solution

Picosecond emission spectroscopy is used to examine the intramolecular charge transfer reaction of N,N-dimethylaminophenyl sulphone in alcohol solution. The effects of nonequilibrium distributions on the reaction surface as well as nonadiabatic effects arising from the time scale of the reactive process and solvent diffusion are discussed. The implications of these data on the motion along the reaction potential energy surface are described.

ChemInform Abstract: PICOSECOND EMISSION SPECTROSCOPY OF TWO PREDISSOCIATIVE ISOMERIC METHYLENEPYRAZOLINES AND PRODUCT TRIMETHYLENEMETHANE

Chemischer InformationsdienstVolume 14, Issue 28 Preparative Organic Chemistry ChemInform Abstract: PICOSECOND EMISSION SPECTROSCOPY OF TWO PREDISSOCIATIVE ISOMERIC METHYLENEPYRAZOLINES AND PRODUCT TRIMETHYLENEMETHANE D. F. KELLEY, D. F. KELLEYSearch for more papers by this authorP. M. RENTZEPIS, P. M. RENTZEPISSearch for more papers by this author D. F. KELLEY, D. F. KELLEYSearch for more papers by this authorP. M. RENTZEPIS, P. M. RENTZEPISSearch for more papers by this author First published: July 12, 1983 https://doi.org/10.1002/chin.198328099Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume14, Issue28July 12, 1983 RelatedInformation

Spectroscopic and picosedond time-resolved studies of vibrational relaxation in naphthazarine in solid neon

Very extensive vibrationally unrelaxed florescence is observed following dye-laser excitation of single vibronic levels of naphthazarine. The rates and pathways of its vibrational relaxation are examined by means of picosecond emission spectroscopy. Analysis of its vibrational and electronic spectra establishes a C 2v symmetry for free naphthazarine.

Picosecond emission spectroscopy of two predissociative isomeric methylenepyrazolines and product trimethylenemethane

Picosecond emission spectroscopy of two predissociative isomeric methylenepyrazolines and product trimethylenemethane

Time resolved picosecond emission spectroscopy of organic dye lasers

A technique is described for the direct measurement of radiationless relaxation in excited molecules by time-resolution of picosecond stimulated emission. Stimulated emission has been observed from unequilibrated vibronic levels of the first excited singlet state in fluid solution. In addition fine-structure has been detected in the stimulated emission.

Picosecond Emission Spectroscopy of Homogeneously Broadened, Electronically Excited Molecular States

We present a direct observation of an ultrafast time-resolved emission spectrum of a dye molecule in solution, the time resolution of the system being 2 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}12}$ sec. Vibrational relaxation within the vibrational manifold of the excited electronic state of rhodamine 6G occurs within 6 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}12}$ sec. We discuss the implications of these results for the understanding of homogeneous broadening of excited electronic states of large molecules.