‘Excimer’ fluorescence V. Influence of solvent viscosity and temperature

1964 ◽  
Vol 280 (1381) ◽  
pp. 289-297 ◽  
Keyword(s):  
Transition Probability ◽  
Radiative Transition ◽  
Quantum Yields ◽  
Excimer Fluorescence ◽  
Diffusion Controlled ◽  
Relative Quantum ◽  
Fluorescence Characteristics ◽  
Steric Configuration ◽  
Monomer Fluorescence ◽  
Influence Of Solvent

The fluorescence characteristics of pyrene solutions in seven different solvents were studied at temperatures from – 100 to 90 °C. Observations were made of the relative quantum yields of excimer and monomer fluorescence and of the fluorescence spectra and time characteristics. The data, which were analyzed to determine the rate parameters and their associated activation energies, are consistent with an excimer formation process which is diffusion-controlled and reversible. The pyrene excimer binding energy B = 0·40 (± 0·01) eV and its radiative transition probability k f D = 1·2 x 10 7 s -1 are independent of the solvent and of the temperature. This indicates that the excimer has a stable steric configuration.

‘Excimer’ fluorescence - X. Spectral studies of 9-methyl and 9, 10-dimethyl anthracene

1966 ◽  
Vol 291 (1427) ◽  
pp. 570-582 ◽  
Keyword(s):  
Transition Probabilities ◽  
Entropy Change ◽  
Radiative Transition ◽  
Fluorescence Yield ◽  
Concentration Quenching ◽  
Spectral Studies ◽  
Quantum Yields ◽  
Excimer Fluorescence ◽  
Excimer Formation ◽  
Monomer Fluorescence

The monomer and excimer fluorescence spectra and quantum yields of solutions of 9-methyl anthracene and 9-10-dimethyl anthracene in several solvents were observed as a function of concentration and temperature ( T ). The monomer and excimer fluorescence quantum efficiencies, the molar excimer/monomer fluorescence yield K , and the Stern–Volmer concentration quenching parameter K' , were determined at room temperature. K was observed as a function of T , and the excimer binding energy B evaluated. At high T, K for a given solute is independent of the solvent, indicating that B , ∆ S , the entropy change on excimer formation, and ( k fD ) 0 /( k fM ) 0 , the ratio of the excimer and monomer radiative transition probabilities in vacuo , are solvent-independent molecular properties. It is proposed that the excimer structure of any compound is similar to that of two adjacent molecules in the crystal lattice, with a reduced intermolecular spacing, and that the excimer fluorescence polarization is that of the 1 L a — 1 A monomer fluorescence. This model accounts for the different types of photodimerization behaviour in the meso -substituted anthracenes. It is proposed that all concentration quenching in aromatic hydrocarbons is due to the formation of excimers and/or stable photodimers.

‘Excimer’ fluorescence VII. Spectral studies of naphthalene and its derivatives

1965 ◽  
Vol 284 (1399) ◽  
pp. 551-565 ◽  
Keyword(s):  
Fluorescence Spectra ◽  
Entropy Change ◽  
Spectral Studies ◽  
Pure Liquid ◽  
Methyl Ethyl ◽  
Excimer Fluorescence ◽  
Mean Values ◽  
Fluorescence Characteristics ◽  
Excimer Formation ◽  
Monomer Fluorescence

The fluorescence spectra of solutions of naphthalene and fourteen of its methyl, ethyl, dimethyl and trimethyl derivatives were observed as a function of molar concentration c at 20 °C and as a function of temperature from 20 to -70 °C. All the compounds show similar excimer fluorescence characteristics with mean values of the excimer binding energy B = 0.28 ± 0.03 eV and of the excimer interaction energy V' m = 0.765 ± 0.03 eV, with the exception of 1,8-dimethyl naphthalene (B = 0.14 eV) in which excimer formation is sterically hindered. The monomer fluorescence quantum efficiencies and ionization potentials were also determined. The fluorescence spectra of liquid 1,6-dimethyl naphthalene and its solutions in three solvents were observed, and the rate parameters and the entropy change ∆ S on excimer formation were determined, B and ∆ S (= -19.1 cal mole -1 deg -1 ) have similar values in the pure liquid and in cis -decalin and dilute ( c ≤ 1 m) cyclohexane solutions, but slight differences occur in n -heptane and concentrated (c > 1 m ) cyclohexane solutions.

Electronic spectroscopy of the transition of DCO and lifetimes and relative quantum yields of the state

2011 ◽  
Vol 270 (1) ◽  
pp. 33-39 ◽  
Author(s):  
Steven J. Rowling ◽  
Scott A. Reid ◽  
Klaas Nauta ◽  
Scott H. Kable
Keyword(s):  
Electronic Spectroscopy ◽  
The State ◽  
Quantum Yields ◽  
Relative Quantum

The Mechanism of the HgH A22Π3/2 → X2Σ+ Emission in the Hg(63P0) Photosensitization of Hydrogen and the Alkanes

1973 ◽  
Vol 51 (8) ◽  
pp. 1207-1214 ◽  
Author(s):  
A. C. Vikis ◽  
D. J. Le Roy
Keyword(s):  
Ground State ◽  
Quantum Yields ◽  
Primary Process ◽  
Relative Quantum

The mechanism of the HgH A22Π3/2 → X2Σ+ emission detected in the Hg(63P0) photosensitized decomposition of H2 and some of the lower alkanes, RH, was investigated. It was concluded that ground state HgH was formed in the primary process Hg(63P0) + RH(or H2) → HgH(X2Σ+) + R(or H). The HgH A22Π3/2 → X2Σ+ emission and presumably the A12Π1/2 → X2Σ+ and B2Σ+ → X2Σ+ emission, also observed in the above systems, result from secondary excitation of ground state HgH on collision with Hg(63P0). Studies of the emission made possible the estimation of relative quantum yields for the above primary process.

scholarly journals The Temperature Dependence of Fundamental Photophysical Properties of [Eu(MeOH-d4)9]3+ Solvates and [Eu.DOTA(MeOH-d4)]- Complexes

2021 ◽  
Author(s):  
Nicolaj Kofod ◽  
Lea Gundorff Nielsen ◽  
Thomas Just Sørensen
Keyword(s):  
Transition Probabilities ◽  
Photophysical Properties ◽  
Transition Probability ◽  
Energy Levels ◽  
Emission Spectra ◽  
Lanthanide Ions ◽  
Quantum Yields ◽  
Luminescence Spectra ◽  
Absorption Cross ◽  
Apparent Lack

The trivalent lanthanide ions show optical transitions between energy levels within the 4f shell. All these transitions are formally forbidden according to the quantum mechanical selection rules used in molecular photophysics. Nevertheless, highly luminescent complexes can be achieved, and terbium(iii) and europium(iii) ions are particularly efficient emitters. This report started when an apparent lack of data in the literature led us to revisit the fundamental photophysics of europium(iii). The photophysical properties of two complexes – [Eu.DOTA(MeOH-d4)]- and [Eu(MeOH-d4)9]3+ – were investigated in deuterated methanol at five different temperatures. Absorption spectra showed decreased absorption cross sections as the temperature was increased. Luminescence spectra and time-resolved emission decay profiles showed a decrease in intensity and lifetime as a temperature was increased. Having corrected the emission spectra for the actual number of absorbed photons and differences in non-radiative pathways, the relative emission probability was revealed. These were found to increase with increasing temperature. The transition probability for luminescence was shown to increase with temperature, while the transition probability for light absorption decreased. The changes in transition probabilities were correlated to a change in the symmetry of the absorber or emitter, with an average increase in symmetry lowering absorption cross section and access to more asymmetric structures increasing the emission rate constant. Determining luminescence quantum yields and the Einstein coefficient for spontaneous emission allowed us to conclude that lowering symmetry increases both. Further, it was found that collisional self-quenching is an issue for lanthanide luminescence, when high concentrations are used. Finally, detailed analysis revealed results that show the so-called ‘Werts’ method’ for calculating radiative lifetimes and intrinsic quantum yields are based on assumption that does not hold for the two systems investigated here. We conclude that we are lacking a good theoretical description of the intraconfigurational f-f transition, and that there are still aspects of fundamental lanthanide photophysics to be explored.<br>

scholarly journals Comparison of photosynthetic fluorescence characteristics of several submerged plants in Honghu Lake, China

2021 ◽  
Vol 49 (2) ◽  
pp. 12173
Author(s):  
Yuan-Qin ZHU ◽  
Bo-Han JING ◽  
Long-Yi YUAN
Keyword(s):  
Pulse Amplitude ◽  
Water Remediation ◽  
Quantum Yields ◽  
Limiting Factor ◽  
Pioneer Species ◽  
Submerged Plants ◽  
Honghu Lake ◽  
Fluorescence Characteristics ◽  
Water Restoration ◽  
Variation Trends

Submerged plants are the pioneer species of eutrophic water remediation, and they are important for maintaining the health of aquatic ecosystem, while light is the main limiting factor for the growth of submerged plants. In this study, we measured the maximal quantum yields of photosystemⅡ(Fv/Fm) and rapid light curves (RLCs) of five dominant submerged macrophytes in situ by using pulse-amplitude modulated fluorometer (Diving-PAM). Results revealed that P. crispus L. and M. verticillatum L. had the highest Fv/Fm value, all species’ Fv/Fm are less than 0.8. In addition, the variation trends of Fv'/Fm' and Fv/Fm were same. All species showed statistically significant differences in α, while P. crispus L. and M. verticillatum L. showed the highest α value in the five species. And the variation trends of rETRm and Ek were basically the same. It indicated that P. crispus L. and M. verticillatum L., both of which had high photosynthetic efficiency, had excellent ability to withstand hard light. Compared five species, P. crispus L. and M. verticillatum L. had resistance capacity to hard light as well as faster photosynthetic rate, and V. natans (Lour.) Hara had higher resistance capacity to low light. Thus, when submerged plants are used for water restoration, V. natans (Lour.) Hara could be regarded as a pioneer species in eutrophication water restoration. P. crispus L. and M. verticillatum L. will have better effects when used in shallow water areas.

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