Metastable Triplet State Research Articles

Triplet state formation and cis → trans isomerization in the excited singlet state of the keto tautomer of 2-(2′-hydroxyphenyl)benzothiazole

Flash-excitation of degassed solutions of 2-(2′-hydroxyphenyl)benzothiazole (HBT) in an inert solvent leads to the metastable triplet state of HBT and to a cis → trans isomerization of the HBT keto tautomer. Both processes proceed from the first excited singlet state of the HBT keto tautomer, 1K*. The trans-keto tautomer is not formed below 150 K, whereas the triplet yield increases at lower temperatures, like the fluorescence yield. Besides fluorescence, intersystem crossing and cis → trans isomerization, an additional deactivation channel of 1K* is proposed in order to explain the different temperature dependencies of the quantum yields of fluorescence and cis → trans isomerization. It is suggested that in the singlet ground state the keto-trans isomer decays by a second-order reaction to the enol form, 1E, by mutual hydrogen exchange: 2 1K tr → 2 1E tr → 2 1E cis.

Transient spectral hole-burning in the S 0→S 1 absorption band of anthracene in a polymethylmethacrylate matrix

The S 0→S 1 absorption band of anthracene in polymethylmethacrylate has been investigated with the technique of transient spectral hole-burning, which makes use of the intermediate population of a metastable triplet state T 1 by intersystem crossing S 1⇝T 1. An experimental technique is described, which is suitable for compounds with triplet lifetimes in the range of milliseconds. Transient holes are detected with conventional absorption spectroscopy (continuous light source with polychromator and optical multichannel detector). Vibronic lifetimes are calculated from the homogeneous widths of resonant transient holes, and vibrational quanta in S 1 are determined from the positions of nonresonant transient holes.

Autoionization rates and energy levels of triplet nf, v=1 Rydberg states of H2.

We have measured the linewidths of 35 different triplet Rydberg states of the ${\mathrm{H}}_{2}$ molecule with quantum numbers n=10--22, L=3, v=1, and R=0--4. An 18-eV electron beam excites a collimated ${\mathrm{H}}_{2}$ beam to the metastable c(2p${)}^{3}$${\mathrm{\ensuremath{\Pi}}}_{\mathit{u}}$ state. Stepwise excitation using two counterpropagating cw single-mode dye laser beams excites the metastable molecule first to an intermediate state [(3d${)}^{3}$\ensuremath{\Sigma} or (3d${)}^{3}$\ensuremath{\Pi}] and then to a triplet nf Rydberg state. The linewidths for the nf Rydberg states give the autoionization rates, which agree satisfactorily with the polarizability--quadrupole-moment long-range interaction model. We also have measured the transition frequencies between these states to an accuracy of 0.002 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. We use these measurements to derive the ionization potential of the metastable triplet state to an accuracy of 0.020 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and the energy difference between the metastable and ground states of ${\mathrm{H}}_{2}$ to an accuracy of 0.025 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$.

Excitation of O 2(a 1Δ g, b 1Σ g+) and I( 2P [formula omitted]) by energy transfer from I 2(A, A′ 3Π 1,2u) in solid rare gases

O 2a 1Δ g, b 1Σ g + → X 3Σ g − and I 2P 1 2 → 2P 3 4 fluorescence occurs in I 2/O 2-doped rare gas matrices when I 2 is excited with visible laser light. O 2(a 1Δ g) and I( 2P 1 2 ) are populated independently by near-resonant energy transfer from the metastable triplet states of I 2. The doublet splitting of the O 2a→X band, which peaks at 7879 and 7863 cm −1 in argon, is interpreted as sensitized emission from O 2 trapped in distinct nearest neighbour positions of the donor 3I 2. Annealing reverses the intensity of the doublet, showing that the sites can be interconverted. It is suggested that the a→X emission rate is enhanced by the sensitizer, causing a lifetime reduction of the a 1Δ g state from 79 s in pure argon to 21 and 3±1 s next to I 2. The long-lived O 2(a 1Δ g) state is the precursor of I 2-sensitized emission from O 2(b 1Σ g +). The lifetime of O 2(b 1Σ g +) is reduced from 24.5 ms in pure argon to 17±1 ms in the presence of I 2.

Triplet State Interrogation in Supersonic Beams by Surface Electron Ejection

AbstractRecently, we have developed an experimental method for the detection of triplet states generated by laser excitation in supersonic beams. It is based on electron ejection from low work‐function surfaces by metastable triplet states. We have detected both directly laser‐excited triplets and triplets generated via intersystem crossing from laser‐excited singlet states. Here, we review the applications of this method and discuss its mechanism. By comparing the laser‐induced fluorescence (LIF) spectrum and Surface Electron Ejection by Laser‐Excited Metastables (SEELEM), we have measured relative triplet formation quantum yields for several aromatic compounds. By utilizing a detector mounted on a translational stage, we could vary the distance between the pulsed laser excitation and the detector and measure the decay rates of triplets in molecular beams. The major advantage of the method is in extending the measurement of triplet lifetimes to the ∼ 1‐ms range. The combination of LIF, SEELEM, and fluorescence quantum yields enabled us to discriminate between intersystem crossing and internal conversion in isoquinoline. SEELEM is now being utilized in studying the spectroscopy and the dynamics of directly laser‐excited triplet states. Although the oscillator strength of the lowest triplet state of pyrazine is about 10−8, we have measured the spectrum and the decay rates of its various vibronic levels. Our results support the notion that surface Penning ionization is the mechanism of SEELEM. The detector is insensitive to vibrational energy (thus enabling the distinction between intersystem crossing and internal conversion). The detection sensitivity of triplets rises with the excess electronic energy and with the lowering of the surface work‐function.

A chemically driven visible laser transition using fast near-resonant energy transfer

Evidence is obtained which demonstrates the potential for developing purely chemical visible lasers based on rapid near-resonant energy transfer from metastable excited triplet states of germanium and silicon monoxide (a/sup 3/ Sigma /sup +/,b/sup 3/ Pi ) to select metal atoms. In this study, the Group IIIA metal atoms were chosen as the energy receptors for the energy transfer-pump sequence. Excited triplet states were generated from the Ge-O/sub 3/, Ge-N/sub 2/, Si-N/sub 2/O, and Si-NO/sub 2/ reactions; the bulk of the experimental results was obtained with a germanium-based system. The energy stored in the long-lived triplet states is transferred to pump X/sup 2/P/sub 1/2/ thallium, indium, and gallium atoms to their lowest lying /sup 2/S/sub 1/2/ states. The authors observe a system of temporal behavior which suggests the creation of a population inversion producing a gain condition and forming the basis for full cavity oscillation on the Tl 7/sup 2/S/sub 1/2/-6P/sub 3/2/ transition at 535 nm. >

Intramolecular proton transfer and tunnel effects in the metastable triplet states of 2-(2′-hydroxyphenyl)benzoxazole studied by micro- and nanosecond laser flash photolysis

The enol-keto tautomerism of 2-(2′-hydrophenyl)benzoxazole (HBO) in its metastable triplet states has been studied in fluid, non-polar solution. After laser flash excitation the keto triplet state is populated with high efficiency. The establishment of a ketoenol equilibrium was observed between 55 and 220 K. At low temperatures the rate of this reaction is determined by tunnel effects. The barrier height of the proton transfer is in the triplet state much larger than in the singlet state.

Delayed S 1→S 0 AND S 2→S 0 fluorescence, delayed excimer fluorescence, and phosphorescence from biphenylene

In liquid solution, the population of the metastable triplet state of biphenylene by triplet energy transfer from a triplet sensitizer leads to different types of delayed luminescence from biphenylene: delayed S 1→S 0 and S 2→S 0 fluorescence and delayed excimer fluorescence due to triplet-triplet annihilation, and phosphorescence. All four delayed luminescences have been observed for the first time.

Delayed Fluorescence of the Kautsky‐Müller Type from Liquid Solutions of Aromatic Compounds and Oxygen

AbstractTriplet‐singlet annihilation (TSA) T, + 1Δg → S1 + 3Σg− of the metastable triplet state (T1) of an aromatic compound and the metastable singlet state (1Δg) of molecular oxygen may lead to an observable delayed fluorescence (DF) S1 → S0 (DF of the Kautsky‐Müller type). A DF of this type has been observed with liquid solutions of phenanthrene and quinoxaline in perfluorohexane and of fluoranthene in 1,1,2‐trichloro‐1,2,2‐trifluoroethane in the presence of oxygen. The DF due to TSA can be kinetically distinguished from the DF due to triplet‐triplet annihilation (TTA). The results indicate a very long lifetime of 1Δg in perhalogenated alkanes. The DF from phenanthrene due to TTA can be assigned to the fluorescence from an excited dimer.

Dual phosphorescence from 2-(2′-hydroxyphenyl)benzoxazole due to keto-enol tautomerism in the metastable triplet state

The photoexcitation of liquid solutions of 2-(2′-hydroxyphenyl)benzoxazole (HBO) in alkanes leads to a dual phosphorescence which can be assigned to the keto and enol forms of HBO. The keto-enol tautomerism in the metastable triplet state of HBO is practically independent of temperature. The keto and enol bands of the phosphorescence from HBO decay monoexponentially with the same rate constant. The experimental data on the phosphorescence from HBO are consistent with those on the transient absorption of HBO. At high triplet concentration and low solvent viscosity, a delayed fluorescence from HBO due to triplet-triplet annihilation is also observed.

Multiexponential decay of the dual phosphorescence from 2-(2′-hydroxyphenyl)benzoxazole in alkane glasses: A simple example of dispersive kinetics

The photoexcitation of 2-(2′-hydroxyphenyl)benzoxazole (HBO) in an alkane glass leads to a time-dependent phosphorescence spectrum and multiexponential decay. The complex kinetic behaviour of this phosphorescence results from the site dependence of the energy difference between the keto and the enol form of HBO in the metastable triplet state. All experimental results can be quantitatively described with the assumption of a Gaussian distribution for this energy difference.

ChemInform Abstract: Two Metastable Triplet States of 2‐Naphthaldehyde at 300 K Corresponding to Twisted and Planar Molecular Geometry. Time‐Resolved Optical Absorption and Raman Spectroscopy.

ChemInform Abstract: Two Metastable Triplet States of 2‐Naphthaldehyde at 300 K Corresponding to Twisted and Planar Molecular Geometry. Time‐Resolved Optical Absorption and Raman Spectroscopy.

Two metastable triplet states of 2-naphthaldehyde at 300 K corresponding to twisted and planar molecular geometry. Time-resolved optical absorption and Raman spectroscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTwo metastable triplet states of 2-naphthaldehyde at 300 K corresponding to twisted and planar molecular geometry. Time-resolved optical absorption and Raman spectroscopyAlexander M. J. Van Eijk, Peter F. A. Verhey, A. Herbert Huizer, and Cyril A. G. O. VarmaCite this: J. Am. Chem. Soc. 1987, 109, 22, 6635–6641Publication Date (Print):October 1, 1987Publication History Published online1 May 2002Published inissue 1 October 1987https://doi.org/10.1021/ja00256a013RIGHTS & PERMISSIONSArticle Views84Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (815 KB) Get e-Alerts Get e-Alerts

Optically enhanced electron attachment.

The first optically enhanced electron attachment involving electronically excited molecules is reported. The metastable (triplet) states responsible for the photoenhanced electron attachment were produced indirectly via internal conversion from higher excited singlet states which are strongly optically allowed and are reached by excimer-laser excitation.

A search for the metastable triplet states of CrO 42− and MnO 4− by transient absorption spectroscopy in crystals at low temperature

Transient absorption on flash excitation at 308 nm is reported for a K 2So 4 crystal doped with CrO 2− 4. The multi-exponential decay and its temperature dependence, between 6 and 125 K, support the assignment to a metastable triplet state of the CrO 2− 4 ion with a fastest decay constant of 200 ns. An experiment on LiClO 4·3H 2O doped with MnO 4 − gave a negative result with the present time resolution of 30 ns.

IR laser chemistry in SO 2. photo-oxidation of CO

By using a cw tunable CO 2 laser, a bimolecular reaction can be induced in a binary SO 2-CO gas mixture with one reactant (SO 2) as photoabsorbing species. The participation of a metastable triplet state of SO 2 responsible for the CO photo-oxidation is demonstrated and the minimum overall internal free energy of the reaction is estimated.

Dynamics of solute-solvent interactions

Abstract

The metastable triplet states of K 2Cr 2O 7 and YVO 4 at 1.2 K: Zero-field splitting and lifetimes of the spin components

The zero-field splittings and lifetimes of the photoexcited triplet states in K 2Cr 2O 7 and YVO 4 crystals have been determined by EPR experiments in zero field. The splittings for K 2Cr 2O 7 agree with the spin Hamiltonian used previously for describing EPR experiments in a magnetic field. Those for YVO 4 indicate a lowering of symmetry of the VO 4 3− ion on excitation.

Magnetic monopole detectors based on He(2(3)S).

Magnetic monopole detectors based on the premise that these particles can create the triplet metastable state in helium, He(${2}^{3}$S), exclusively and without ionization are believed to be feasible. In one of these, He(${2}^{3}$S) is detected in an ionization chamber array using both pure helium and a mixture of He+${\mathrm{N}}_{2}$ in which Penning ionization occurs. In the second version, resonance ionization spectroscopy is used to selectively ionize He(${2}^{3}$S). In both cases, monopoles with velocities greater than ${10}^{\mathrm{\ensuremath{-}}4}$c can be searched for with both large and reliable detectors.

Complete determination of 14N hyperfine and quadrupole interactions in the metastable triplet state of free-base porphin via electron spin echo envelope modulation

Through the use of the electron spin echo envelope modulation method, we have accomplished the complete determination of the 14N hyperfine and quadrupole interaction tensors in the lowest photo-excited triplet state of free-base porphin in an n-octane single crystal at ∼1.4 K. The results give insight into the molecular structure of the porphin in the excited state, the relationship between the nitrogen spin density and observed hyperfine couplings, and the effect of hydrogen bonding interactions on the quadrupole coupling constants and principal axes.