Emission and Deactivation of the Excited States of 2,3-Pentanedione

1972 ◽  
Vol 50 (9) ◽  
pp. 1338-1344 ◽  
Author(s):  
A. W. Jackson ◽  
A. J. Yarwood
Keyword(s):  
Triplet State ◽  
Gas Phase ◽  
Excited States ◽  
Singlet State ◽  
Triplet States ◽  
Excited Singlet ◽  
Vibrationally Excited ◽  
Singlet Level ◽  
Singlet And Triplet States ◽  
Fluorescence And Phosphorescence

Vibrationally excited singlet and triplet states of 2,3-pentanedione are formed by photolysis at 365 nm. The processes removing these excited states in the gas phase are studied by measuring the fluorescence and phosphorescence yields. Fluorescence can occur from the vibrationally excited, as well as the vibrationally equilibrated, singlet state. The fluorescence and phosphorescence data are considered in terms of mechanisms which involve either weak or strong collisions. Although the data cannot distinguish between the alternatives, there are two significant conclusions. The fluorescence data require that emission occur from at least two levels in the singlet manifold. To explain the phosphorescence data, the highest emitting singlet level must not lead to a vibrationally equilibrated triplet state.

The radiation-induced formation of excited states of aromatic hydrocarbons in benzene and cyclohexane, II. Yields of excited singlet and triplet state solute molecules

1972 ◽  
Vol 328 (1575) ◽  
pp. 457-479 ◽  
Keyword(s):  
Excited States ◽  
Pulse Radiolysis ◽  
Singlet State ◽  
Relative Yield ◽  
Excited Singlet State ◽  
High Yield ◽  
Triplet States ◽  
Excited Singlet ◽  
Concentration Dependences ◽  
Radiation Induced

The concentration dependences of the yield of excited triplet states, G ( 3 S*), and the concentration dependences of the relative yield of radiation-induced fluorescence obtained on pulse radiolysis of solutions of naphthalene, anthracene, pyrene and 2,5-diphenyloxazole (PPO) are reported. The yields of excited singlet state solute molecules, G ( 1 S*), formed on pulse radiolysis of naphthalene-cyclohexane and naphthalene-benzene solutions has been determined by comparing the intensity of the radiation-induced fluorescence with that obtained on photo-excitation. It is concluded that intersystem crossing (i.s.c.) from the excited singlet state is an important process in the formation of the high yield of triplet excited states of the solute. Under certain conditions this process accounts for up to 50 % of G ( 3 S*) in cyclohexane and the entire G ( 3 S*) in benzene solutions.

Molecular orbital studies of the singlet and triplet states of formylmethylene conformers

1991 ◽  
Vol 69 (11) ◽  
pp. 1630-1635 ◽  
Author(s):  
Ratnakar K. Gosavi ◽  
Manuel Torres ◽  
Otto P. Strausz
Keyword(s):  
Singlet State ◽  
Closed Shell ◽  
Basis Set ◽  
Planar Geometry ◽  
Present Calculation ◽  
Triplet States ◽  
Excited Singlet ◽  
Singlet And Triplet States ◽  
Ci Calculations ◽  
Single Configuration

The energies and geometries of the low-lying electronic states of formylmethylene have been calculated at the SCF and CI levels using 6-31G** basis set. In agreement with previous reports and accumulated experimental observations, the ground state is the carbenoid triplet with a planar geometry. Also, in agreement with all previous single configuration SCF and CI calculations, the lowest excited singlet state is computed to be the nonplanar closed shell carbenoid structure. In contrast, accumulated experimental evidence along with previously reported MC–SCF results require this state to be planar. The present calculation predicts the existence of a (σ–σ) 1,3-diradical 1A′ state, which appears to be identical to the MC–SCF lowest singlet state, but this state lies some 11 kcal/mol above the closed shell carbenoid 1A state. Apparently, single configuration SCF methods are inadequate for the correct description of the electronic manifold of formylmethylene. Key words: formylmethylene, singlet and triplet states, ab initio MO calculations, conformers, molecular structure.

The mechanism of the gas phase photolysis of acetone

1966 ◽  
Vol 290 (1423) ◽  
pp. 563-582 ◽  
Keyword(s):  
Gas Phase ◽  
Order Rate Constant ◽  
Electronic Energy ◽  
Intersystem Crossing ◽  
Triplet States ◽  
Excited Singlet ◽  
First Order ◽  
Electronic Energy Transfer ◽  
Vibrational Levels ◽  
Singlet And Triplet States

A mechanism for the photolysis of acetone has been derived from experimental data including studies on the photosensitized isomerization of olefines. Dissociation into methyl and acetyl radicals occurs from both the first excited singlet and triplet states; the rate constants for excitation by light of 3130 Å wavelength are 2.5 x 10 16 exp ( —16900/ RT ) and 2.5 x 10 10 exp ( — 6400/ RT ) 1. mole -1 s -1 respectively. At low intensities of absorption, decomposition of acetyl radicals predominates over radical-radical interactions. The triplet state is extensively populated at moderate temperatures, the yield at 48 °C being 0.98. The low phosphorescence efficiency of acetone can be ascribed to intersystem crossing to the ground state for which the first order rate constant is 1.25 x 10 5 s -1 . The isomerization data requires the recognition of at least two vibrational levels of the acetone triplet, the rate of electronic energy transfer depending upon the excess energy possessed by the donor

scholarly journals Photophysical Properties of Nitrated and Halogenated Phosphorus Tritolylcorrole Complexes: Insights from Theory

Molecules ◽  
2018 ◽  
Vol 23 (11) ◽  
pp. 2779 ◽  
Author(s):  
Marta Alberto ◽  
Bruna De Simone ◽  
Gloria Mazzone ◽  
Nino Russo ◽  
Marirosa Toscano
Keyword(s):  
Excited States ◽  
Density Functional ◽  
Energy Gap ◽  
Photophysical Properties ◽  
Intersystem Crossing ◽  
Triplet States ◽  
Excited Singlet ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Singlet And Triplet States

The photophysical properties of a series of nitrated and halogenated phosphorus tritolylcorrole complexes were studied in dichloromethane solvent by using the density functional theory. Particular emphasis was given to the absorption spectra, the energy gap between the excited singlet and triplet states, and the magnitude of the spin-orbit couplings for a series of possible intersystem crossing channels between those excited states. The proposed study provides a better description of the photophysical properties of these systems while giving insights into their possible use as photosensitizers in photodynamic therapy.

Violation of Hund's multiplicity rule in the electronically excited states of conjugated hydrocarbons

1985 ◽  
Vol 63 (7) ◽  
pp. 1572-1579 ◽  
Author(s):  
Shiro Koseki ◽  
Takeshi Nakajima ◽  
Azumao Toyota
Keyword(s):  
Triplet State ◽  
Excited States ◽  
Singlet State ◽  
Basis Set ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Electronically Excited States ◽  
Conjugated Hydrocarbons ◽  
Electronically Excited ◽  
Linear Polyenes

Violation of Hund's multiplicity rule in the electronically excited states of conjugated hydrocarbons is studied by using the Pariser–Parr–Pople type SCF MO method and the abinitio MO method with STO-3G basis set, both methods being augmented by CI-type treatments. It is shown that for symmetrical structures (D2h) of the nonalternant hydrocarbons, propalene, pentalene, and heptalene, the lowest excited singlet state is energetically lower than the corresponding triplet state. This is mainly due to the spin polarization (SP) effects. For D2h, structures of pentalene and heptalene the open-shell excited singlet state is predicted to be lower in energy than the closed-shell state, with the result that the former is really the ground state. Further, calculations made by including electron correlation effects reveal that in linear polyenes and polyacenes, the lowest excited singlet "minus" state (using Pariser's classification of the alternancy symmetry species) is lower in energy than the corresponding triplet state. The energy lowering of the singlet "minus" state in linear polyenes is due mostly to the mixing with the doubly excited configurations (mm → nn), while the considerable part of it in polyacenes is due to the SP effects.

Lifetime studies of the biacetyl excited singlet and triplet states in the gas phase at 25.deg.

1972 ◽  
Vol 94 (1) ◽  
pp. 13-19 ◽  
Author(s):  
Howard W. Sidebottom ◽  
Charles C. Badcock ◽  
Jack G. Calvert ◽  
Blaine R. Rabe ◽  
Edward K. Damon
Keyword(s):  
Gas Phase ◽  
Triplet States ◽  
Excited Singlet ◽  
Singlet And Triplet States ◽  
Lifetime Studies

Low-lying activated states of chloroiridium phthalocyanine aggregates in glassy solution at low temperatures

1988 ◽  
Vol 66 (1) ◽  
pp. 86-92 ◽  
Author(s):  
W.-H. Chen ◽  
K. E. Rieckhoff ◽  
E.-M. Voigt
Keyword(s):  
Singlet State ◽  
Torsional Oscillation ◽  
Zero Point ◽  
Triplet States ◽  
Excited Singlet ◽  
Glassy Solution ◽  
Ground Singlet State ◽  
Modes Of Vibration ◽  
State Formula ◽  
Singlet And Triplet States

Studies of phosphorescence intensities and lifetimes of two chloroiridium phthalocyanine aggregates in α-chloronaphthalene between 5 and 80 K have revealed the existence of low-lying activated states only a few tens of cm−1 above the zero-point vibration in both lowest singlet and triplet states. From the data, activation energies of intersystem crossings between the two multiplicities associated with these states have been obtained as follows: for crossing from the first excited singlet to the lowest triplet state, Ea = 42 ± 10 and 29 ± 10 cm−1, respectively, for the two aggregates; for crossing from the lowest triplet to the ground singlet state, [Formula: see text] and 23 ± 5 cm−1, respectively. These activated states are tentatively attributed to certain intermolecular modes of vibration in aggregates. Specifically, they fit the model of molecular torsional oscillation of two and three parallel-sheet arrangements. On the basis of these findings, we propose that the first Ea (or [Formula: see text]) is the fundamental librational frequency of the dimer and the second Ea (or [Formula: see text]) is that for the trimer.

Parsorbitalm ethode, 6. Mitt. : 1Charakterordnungen angeregter Zustände 2/ Character Orders of Excited States

1974 ◽  
Vol 29 (3) ◽  
pp. 529-530
Author(s):  
Oskar E. Polansky
Keyword(s):  
Excited States ◽  
Triplet States ◽  
Reaction Paths ◽  
Excited Singlet ◽  
Complete Neglect ◽  
Singlet And Triplet States

In spite of the complete neglect of spins in HMO theory different character orders are obtained for the lowest excited singlet and triplet states. Since 3φʟ* > 1φʟ*, possibly the typical reaction paths of tripletts are mainly determined by electronic factors

Photolysis of SO2 in the Presence of Foreign Gases. VI. Acetylene and Allene

1974 ◽  
Vol 52 (20) ◽  
pp. 3451-3453 ◽  
Author(s):  
Menachem Luria ◽  
Julian Heicklen
Keyword(s):  
Triplet State ◽  
Gas Phase ◽  
Triplet States ◽  
Relative Importance ◽  
Excited Singlet ◽  
Singlet States ◽  
Excited Singlet States ◽  
Allene System

The photolysis of SO2 at 3130 Å and 25 °C in the presence of C2H2 leads to CO, and, in the presence of allene to CO and C2H4 as gas phase products. In the C2H2 system, the CO comes from the two non-emitting triplet states of SO2, 57% from SO2** and 43% from SO2≠. In the allene system, the two excited singlet states of SO2, and possibly the emitting triplet state, also participate. The relative importance of the contributions from each state can be estimated to be >35% from 1SO2, <16% from 3SO2, 8% from SO2*, 12% from SO2**, and 29% from SO2≠.

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