Solvent and temperature dependence of absorption and phosphorescence of trans-diisothiocyanate (bis)ethylenediaminechromium(III) ion

1984 ◽  
Vol 62 (4) ◽  
pp. 703-706 ◽  
Author(s):  
Cooper H. Langford ◽  
Thomas M. Schear
Keyword(s):  
Absorption Maximum ◽  
Unusual Case ◽  
Activation Parameters ◽  
Donor Number ◽  
Quantum Yields ◽  
Intersystem Crossing ◽  
Phosphorescence Emission ◽  
Solvent Shifts ◽  
Donor Numbers ◽  
Decay Path

An unusual case of absorption and fluorescence bands shifting in the same direction as solvent varies is reported. Solvent shifts in the quartet absorption maximum and doublet or phosphorescence emission maximum of trans-Cren2(NCS)2+ ion are related to the Gutmann solvent donor number. The correlation is discussed in terms of solvent effects on the vibrations identified as responsible for the vibronic transitions and are in agreement with Hollebone's notion of "vibronic" intersystem crossing. The activation parameters for decay of phosphorescence in eight solvents correlate by a Barclay–Butler plot and are consistent with the possibility of a single common dominant mechanism for the T-dependent decay path. They do not, however, depend on solvent donor numbers as quantum yields for substitution do. Therefore, they offered no new support for the notion that the pathway is by chemical reaction. The activation parameters also fail to correlate with solvent fluidity.

The Photolysis in Acidic Aqueous Solutions of the Monooxalato-bisethylenediamine Chromium(III) Cation and the Bisoxalatomonoethylenediamine Chromate(III) Anion: Photolysis Modes and Quantum Yields

1971 ◽  
Vol 49 (3) ◽  
pp. 375-383 ◽  
Author(s):  
A. D. Kirk ◽  
K. C. Moss ◽  
J. G. Valentin
Keyword(s):  
Quantum Yield ◽  
Aqueous Solutions ◽  
Quantum Yields ◽  
Ligand Field ◽  
Intersystem Crossing ◽  
Empirical Correlations ◽  
Complex Ions ◽  
Ethylenediamine Complex ◽  
Ethylenediamine Ligand ◽  
Ph Range

The photolysis reactions of the complex ions [Cr(en)2ox]+ and [Cren(ox)2]− have been studied in the pH range 1 → 3 and at temperatures from 0 to 25 °C. It has been found that both ions photoaquate to a monodentate protonated ethylenediamine complex which then undergoes further aquation thermally with loss of the ethylenediamine ligand. Quantum yields for these aquations were measured for irradiation into the ligand field bands, the values obtained being 0.18 and 0.02, respectively. The results are discussed in terms of known empirical correlations for Cr(III) complexes. Assuming these reactions may occur from the 4T2g state as precursor, arguments are presented that the correlation between quantum yield and ΔE may depend on mixing of the 4T2g and 2Eg states, and its effect on the intersystem crossing rate constant.

Luminescence of 5-Phenyltetrazole and its Derivatives. Part II. Phosphorescence

1984 ◽  
Vol 39 (6) ◽  
pp. 556-559 ◽  
Author(s):  
I. Gryczyński ◽  
A. Kawski ◽  
Z. Grzonka ◽  
A. Rażyńska
Keyword(s):  
Triplet State ◽  
Quantum Yields ◽  
Intersystem Crossing ◽  
Thermal Deactivation ◽  
Fluorescence Quantum Yields ◽  
Radiative Transitions ◽  
Polyvinyl Alcohol Film ◽  
Methyl Derivatives ◽  
Temperature Responses ◽  
Phosphorescence Spectra

The phosphorescence spectra, mean lifetimes of phosphorescence and ratios of phosphorescence/ fluorescence quantum yields have been measured for 5-phenyltetrazole and its three methyl derivatives in a polyvinyl alcohol film over the temperature range of (77-250) K. Temperature responses of the non-radiative intersystem crossing constant. KST, and the non-radiative triplet state deactivation constant, km, have been investigated on the basis of these measurements. The energy of activation for the non-radiative transitions has been determined. With the methyl 5-phenyltetrazoles, the thermal deactivation of the triplet state, contrary to the intersystem crossing, has been found to be influenced by the position of the methyl substituent in the phenyl ring.

scholarly journals A Singlet Oxygen Photogeneration and Luminescence Study of Unsymmetrically Substituted Mesoporphyrinic Compounds

2009 ◽  
Vol 2009 ◽  
pp. 1-10 ◽  
Author(s):  
Anabela Sousa Oliveira ◽  
Dumitru Licsandru ◽  
Rica Boscencu ◽  
Radu Socoteanu ◽  
Veronica Nacea ◽  
...  
Keyword(s):  
Singlet Oxygen ◽  
Photophysical Properties ◽  
Delayed Fluorescence ◽  
Quantum Yields ◽  
Mean Values ◽  
Oxygen Generation ◽  
Fluorescence Quantum Yields ◽  
Thermally Activated ◽  
Phosphorescence Emission ◽  
Photophysical Studies

This paper deals with a series of new unsymmetrically substituted mesoporphyrins: 5-(2-hydroxyphenyl)-10,15,20-tris-phenyl-21,23-H-porphyrin (TPPOHO), 5-(3-hydroxyphenyl)-10,15,20-tris-phenyl-21,23-H-porphyrin (TPPOHM), 5-(4-hydroxyphenyl)-10,15,20-tris-phenyl-21,23-H-porphyrin (TPPOHP), 5-(2-hydroxyphenyl)-10,15,20-tris-butyl-21,23-H-porphyrin (TBPOHO), and their parent nonsubstituted compounds, respectively, 5,10,15,20-tetrakis-phenyl-21,23-H-porphyrin (TPP) and 5,10,15,20-tetrakis-butyl-21,23-H-porphyrin (TBP). Several photophysical studies were carried out to access the influence of the unsymmetrical substitution at the porphyrinic macrocycle on porthyrin's photophysical properties, especially porthyrin's efficiency as singlet oxygen sensitizers. The quantum yields of singlet oxygen generation were determined in benzene (ΦΔ(TPP) = 0.66 ± 0.05;ΦΔ(TPPOHO) = 0.69 ± 0.04;ΦΔ(TPPOHM) = 0.62 ± 0.04;ΦΔ(TPPOHP) = 0.73 ± 0.03;ΦΔ(TBP) = 0.76 ± 0.03;ΦΔ(TBPOHO) = 0.73 ± 0.02) using the 5,10,15,20-tetraphenyl-21,23-H-porphine (ΦΔ(TPP) = 0.66) and Phenazine (ΦΔ(Phz) = 0.83) as reference compounds. Their fluorescence quantum yields were found to be (Φf(TPPOHO) = 0.10 ± 0.04;Φf(TPPOHM) = 0.09 ± 0.03;Φf(TPPOHP) = 0.13 ± 0.02;Φf(TBP) = 0.08 ± 0.03 andΦf(TBPOHO) = 0.08 ± 0.02 using 5,10,15,20-tetraphenyl-21,23-H-porphine as referenceΦf(TPP) = 0.13). Singlet state lifetimes were also determined in the same solvent. All the porphyrins presented very similar fluorescence lifetimes (mean values ofτS(withO2, air equilibrated) = 9.6 ± 0.3 nanoseconds and (withoutO2, argon purged) = 10.1 ± 0.6 nanoseconds, resp.). The phosphorescence emission was found to be negligible for this series of unsymmetrically substituted mesoporphyrins, but an E-type, thermally activated, delayed fluorescence process was proved to occur at room temperature.

Photochemistry of cyclododecanone

1976 ◽  
Vol 29 (11) ◽  
pp. 2477 ◽  
Author(s):  
PJ Burchill ◽  
AG Kelso ◽  
AJ Power
Keyword(s):  
Cleavage Product ◽  
Quantum Yields ◽  
Intersystem Crossing ◽  
Quantitative Measurements ◽  
Acyclic Ketones ◽  
Triplet Lifetime

Quantitative measurements of the photolytic reactions of cyclododecanone gave quantum yields of reaction and of intersystem crossing as 0.56 and 0.88 respectively, and a triplet lifetime of 1.7 x 10-7 s. Cyclobutanol formation accounts for most of the reaction with only a low yield of the Norrish II cleavage product; this contrasts markedly with the opposite behaviour of acyclic ketones of similar size. The results may be explained by the apparent restriction of rotation in cyclododecanone molecules.

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