Room Temperature Fluorescence Spectra Research Articles

Fluorescence charactersitics of β-carboline alkaloids in highly concentrated hydroxide solutions

The room temperature electronic absorption and fluorescence spectra of the pharmacologically active β-carboline alkaloids norharman, harmane, harmine, harmaline, reserpine and yohimbine are measured in moderately and highly concentrated hydroxide solutions. The appearance of a new fluorescence emission band in the latter madia for all the compounds under study was ascribed to anions in which the NH group of the indole ring is deprotonated. The differences between the acidities of their excited singlet states and their ground states are estimated by means of the Förster-Weller cycles.

Effect of pH on the fluorescence and phosphorescence spectra of indolecarboxylic acids. Evidence for the existence of a singlet excited-state indole acid dianion

Room-temperature electronic absorption, fluorescence, and low-temperature (77 K) phosphorescence spectra of a series of indolecarboxylic acids have been measured in predominantly aqueous solutions at pH 1.2, 7.0, 12.5, and in 5 N NaOH. The 1L a and 1L b π, π ∗ states have been assigned to the electronic transitions for all the compounds under study. The quenching of fluorescence, the appearance of a new fluorescence emission band, red-shifted by 40 nm, in very alkaline media, and the disappearance of the indole carboxylate short-wavelength band have been attributed to the formation of an excited singlet-state indolate carboxylate (dianion) stabilized by hydrogen bonding with the solvent. The existence of two successive excited singlet-state prototropic equilibria is discussed.

Solid-surface derivative room-temperature luminescence spectrometry of mixtures

Derivative solid-surface room-temperature fluorescence and phosphorescence were combined for the identification of components in binary and ternary mixtures of nanogram amounts of nitrogen heterocycles. Direct, and first and second derivative room-temperature phosphorescence excitation, room-temperature fluorescence and room-temperature phosphorescence spectra were used in the identification of the components in the mixtures by matching spectral wavelengths from mixtures with spectral wavelengths from standards. The criteria for matching wavelengths, subtracting background signals and obtaining derivative spectra at the 0.5-ng level are discussed.

Luminescence determination of benzoquinoline isomers in complex samples

The room-temperature phosphorescence (r.t.p.) and fluorescence spectra of benzoquinoline isomers are investigated. The isomers can be resolved into the linear or angular subgroups on the basis of their fluorescence and r.t.p. spectra by using conventional fixed excitation. Second-derivative and synchronous scanning techniques can be combined to improve the selectivity of the r.t.p. and fluorescence methods. These simple luminescence techniques were used to estimate three benzoquinoline isomers in a coal tar fraction. Direct analysis of this complex sample allowed acridine to be estimated and upper limits to be provided for benzo(h)quinoline and phenanthridine; the presence of three other isomers was not detected. Comparative studies with data obtained by high-performance liquid chromatography are reported.

Fluorescence of inversion site Cr3+ ions in alexandrite

A c-axis alexandrite laser rod was longitudinally pumped in the 450–560 nm region with argon ion and dye lasers. In addition to the sharp R lines and broadband phonon-assisted transitions typical of mirror site Cr3+ ions in alexandrite, room temperature fluorescence spectra displayed characteristics in the 690–730 nm region which were maximal when pumped at 496.5 nm but were nearly absent when pumped at 457.9 nm and 560 nm. Time-dependent fluorescence measurements with pulsed excitation yielded two lifetimes, 310 μs and 44 ms. The short lifetime component is mirror site fluorescence. The long lifetime component is typical for Cr3+ ions in inversion symmetry sites and its presence correlates with the pump wavelength dependent features. Inversion site fluorescence consists of magnetic dipole R lines at 690.0 nm and 695.8 nm and phonon-assisted electric dipole transitions at longer wavelengths.

Photochemistry and photophysics of phenylmethyl radicals

The photophysics of arylalkyl radicals, notably that of the prototype benzyl radical (PhCH/sub 2//sub ./), have been extensively studied. Fluorescence lifetimes and quantum yields have been experimentally measured in solid matrices at low temperatures and theoretical calculations have estimated the energy levels and the various decay modes of a variety of substituted benzyl radicals. Fluorescence from the closely related diphenylketyl radical has also been observed in a glassy matrix as well as at room temperature. For the ketyl radical the fluorescence lifetime has decreased from approx. 20 to approx. 2 ns on increasing the temperature from 77 K to room temperature, indicating a possible photochemical reaction of the excited state of the radical at the higher temperature. While the fluorescence lifetime of the benzyl and its analogue radicals at 77 K is in the range of 1.0 +/- 0.5 ..mu..s, no information is available in the literature on their fluorescence lifetime at higher temperatures. In fact, information on the photochemistry and photophysics of radicals in liquid solutions is very scarce. To bridge this gap a systematic study of such systems has been initiated. In the present communication, the room temperature lifetime, excited-state doublet-doublet and fluorescence spectra of the diphenylmethyl radicalmore » are reported as well as the photochemistry of its triphenylmethyl homologue. 18 references, 2 figures.« less

Intramolecular Vibrational Redistribution at Low State Densities in S1 Aromatics. Evidence for Rotational Contributions

Evidence is presented concerning the onset of intramolecular vibrational redistribution (IVR) as one climbs the vibrational manifold of room temperature S1 aromatics. The onsets of IVR occur at S1 vibrational energies between 670 and 2000 cm−1 for various single and double ring aromatic molecules. The vibrational level densities in the onset region seem too small to support the extensive IVR that is observed in every molecule. Comparisons of room temperature fluorescence spectra with cold supersonic beam spectra from p-difluorobenzene support the proposition that Coriolis vibration–rotation coupling makes important contributions to the effective density of states in room temperature IVR.

Some Pattern Recognition Considerations for Low-Temperature Luminescence and Room Temperature Fluorescence Spectra

Low-temperature (77 K) luminescence (LTL) and room temperature fluorescence (RTF) spectra of polynuclear aromatic hydrocarbons with varying amounts of spectral structure are studied as a function of several instrument parameters (emission slit width, scan speed, and damping) in order to develop quantitative criteria for spectral quality and reproducibility. The purpose of this study is to assess the classification and pattern recognition capabilities for hazardous chemicals for various spectral techniques and to develop suitable spectral libraries and search routines. In order to quantitate the effect of the instrument parameters on the spectrum, a statistic (power) was used to measure spectral quality. In addition, three measures of similarity, used for assessing the agreement between two patterns (spectra), were evaluated to determine the variability that can be expected in spectra obtained under the same and different instrumental conditions. Analysis of the data confirms that the low-temperature luminescence technique produces better quality spectra than the room temperature fluorescence technique, but that room temperature fluorescence spectra are more repeatable.

Photoluminescence Study in Polymers

Photoluminescence from polymer films of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyparaxylylene (Parylene N) and polymonochloroparaxylene (Parylene C) was investigated. Room temperature fluorescence spectra of these polymers were considered to be composed of a monomer emission and an excimer emission. Luminescence at 88 K showed structured phosphorescence in addition to the fluorescence emission observed at room temperature. The chemical substitution of a hydrogen atom in benzene rings by a chlorine atom or carbonyl groups mainly affected the monomer fluorescence emission.

Absorbance and fluorescence properties of the bacteriochlorophyll a reaction center complex and bacteriochlorophyll a protein in green bacteria

Absorbance, emission and excitation spectra were measured at both room and liquid-nitrogen temperatures for a photochemically active bacteriochlorophyll a reaction center complex and a bacteriochlorophyll a protein isolated from Chlorobium limicola and Chlorobium thiosulfatophilum. The low-temperature absorbance spectrum for the complex has a band centered at 833 nm, which is not seen in the spectrum of the bacteriochlorophyll a protein. We attribute this difference to a modification of the bacteriochlorophyll a protein in the active complex. The room-temperature fluorescence spectra for the bacteriochlorophyll a protein and the complex are similar, as are those measured at low temperatures. The 833-nm component of the low-temperature absorbance spectrum of the complex is relatively nonfluorescent.