Electronic energy transfer in bichromophoric molecular clusters (original) (raw)
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Dual fluorescence and intramolecular electronic energy transfer in a bichromophoric molecule
The Journal of Physical Chemistry, 1980
The bichromophoric molecule containing phenanthrene and a-diketone moieties connected by two chains of five methylene groups has been studied. Most spectroscopic properties of this molecule are described by a superposition of those of its constituent chromophores. Unique for the combined molecule is the fact that energy absorbed by the phenanthrene chromophore is transferred in part to the a-diketone and both chromophores emit their characteristic fluorescence spectra. An extensive study was made of the intramolecular energy transfer process in solution as a function of the excitation frequency and of the sample temperature. It was clearly demonstrated that energy is transferred very efficiently to the a-diketone moiety from a thermally activated state of the bichromophoric molecule. The rate of this energy transfer is comparable to the relaxation rate of the activated state. In contrast, the transfer process from the ground vibrational level of the first excited state of the phenanthrene moiety is rather slow (-lo7 d).
The mechanism of short-range intramolecular electronic energy transfer in bichromophoric molecules
The Journal of Physical Chemistry, 1984
A study of intramolecular energy transfer (intra-ET) in a series of bichromophoric molecules consisting of cyclic a-diketones incorporating an ortho-, meta-, or para-substituted benzene ring is reported. Most spectroscopic properties of these molecules are described by a superposition of those of their constituent chromophores. Unique for the bichromophore molecule is the fact that, depending on the molecular geometry, energy absorbed by the aromatic chromophore is transferred in part to the a-diketone and both chromophores emit their characteristic fluorescence spectra. An extensive study was made of the intramolecular electronic energy transfer process in solution as a function of temperature. The results indicate that the transfer efficiency is strongly structure dependent suggesting that a Dexter type exchange interaction is responsible for singlet-singlet intra-ET between close chromophores in a bichromophoric molecule. The thermal dependence observed in some cases is attributed to conformational factors. A general theoretical analysis of intra-ET in bichromophoric molecules provides expressions for donor fluorescence decay and for its fluorescence quantum yield in terms of the average distance between donor and acceptor moieties and the flexibility of the chains connecting donor and acceptor. Comparison with the present experimental data supports the predictions of this analysis. It is concluded that intra-ET in bichromophoric molecules is indeed governed by short-range exchange interactions.
Supersonic jet spectroscopy of naphthalene–fluorene bichromophoric cluster
Journal of Photochemistry and Photobiology A: Chemistry, 2002
We have investigated the supersonic jet spectroscopy and photophysics of 1-methylnaphthalene-fluorene (1MN-FL) cluster, and looked for indications of intramolecular electronic energy transfer (Intra-EET) from the FL (donor, D) to 1MN (acceptor, A). The clusters were identified by their time of flight (TOF) mass spectra. We observed clusters bands in the LIF spectrum near the region of 1MN origin. We have also observed cluster TOF-resonance enhanced multi-photon ionization (REMPI) spectrum near the electronic origin of the fluorene moiety. However, this spectrum was almost independent of the excitation wavelength, and was not observed in the LIF spectrum. This is probably due to fast Intra-EET resulting in lifetime broadening of the donor chromophore cluster spectrum, similar to that observed previously for the naphthalene-anthracene bichromophoric system.
The ultrafast energy transfer process in naphtole–nitrobenzofurazan bichromophoric molecular systems
Journal of Photochemistry and Photobiology A: Chemistry, 2007
This work presents an experimental and computational study of the intramolecular electronic energy transfer process occurring in two newly synthesized bichromophoric species: )oxy]acetate (r-Bi). In both f-Bi and r-Bi the donor chromophore is the [(4-chloro-1-naphthyl)oxy]acetate moiety, whereas the acceptor units belong to the family of the 4dialkylaminonitrobenzoxadiazoles, well-known fluorescent probes. The two bichromophores differ in the structural flexibility. In f-Bi, acceptor and donors are linked by a diethanolamine moiety, whereas in r-Bi through a (3S, 4S)3,4-dihydroxypyrrolidine ring. By means of steady-state and timeresolved UV-vis spectroscopies we carried out a detailed analysis of the photo-response of donor and acceptor chromophores as individual molecules and when covalently linked in f-Bi and r-Bi. The intramolecular energy transfer process occurs very efficiently in both the bichromophores. The rate constant and the quantum efficiency of the process are k ET = (2.86 ± 0.16) × 10 11 s −1 and Q = 0.998 in f-Bi, and k ET = (1.25 ± 0.08) × 10 11 s −1 and Q = 0.996 in r-Bi. Semiempirical calculations were utilized to identify the energy and the nature of the electronic states in the isolated chromophores. Molecular mechanics calculations have been performed to identify the most stable structures of the bichromophoric compounds. The predictions of Förster theory are consistent with the experimental results and provide a suitable way to evaluate the structural differences between the two compounds.
Chemical Physics Letters, 1998
Intramolecular electronic relaxation processes in a flexible naphthalene-acridine bichromophoric molecule I were studied Ž . in solution and in a supersonic jet expansion. Intramolecular electronic energy transfer intraEET from the electronically excited naphthalene unit to the acridine moiety and an additional non-radiative decay process, probably intramolecular Ž . electron transfer intraELT to the acridine unit, of the excited naphthalene group was observed in solution. In a supersonic jet expansion, no indication for intraEET or other interchromophoric interactions was found. The relaxation of the excited naphthalene chromophore in I, under the conditions of supersonic jet expansion, is dominated by intrachromophoric radiationless transitions. The dependence of single vibronic fluorescence lifetimes of jet-cooled I on the excitation frequency is discussed. q
… of Photochemistry and …, 2007
This work presents an experimental and computational study of the intramolecular electronic energy transfer process occurring in two newly synthesized bichromophoric species: )oxy]acetate (r-Bi). In both f-Bi and r-Bi the donor chromophore is the [(4-chloro-1-naphthyl)oxy]acetate moiety, whereas the acceptor units belong to the family of the 4dialkylaminonitrobenzoxadiazoles, well-known fluorescent probes. The two bichromophores differ in the structural flexibility. In f-Bi, acceptor and donors are linked by a diethanolamine moiety, whereas in r-Bi through a (3S, 4S)3,4-dihydroxypyrrolidine ring. By means of steady-state and timeresolved UV-vis spectroscopies we carried out a detailed analysis of the photo-response of donor and acceptor chromophores as individual molecules and when covalently linked in f-Bi and r-Bi. The intramolecular energy transfer process occurs very efficiently in both the bichromophores. The rate constant and the quantum efficiency of the process are k ET = (2.86 ± 0.16) × 10 11 s −1 and Q = 0.998 in f-Bi, and k ET = (1.25 ± 0.08) × 10 11 s −1 and Q = 0.996 in r-Bi. Semiempirical calculations were utilized to identify the energy and the nature of the electronic states in the isolated chromophores. Molecular mechanics calculations have been performed to identify the most stable structures of the bichromophoric compounds. The predictions of Förster theory are consistent with the experimental results and provide a suitable way to evaluate the structural differences between the two compounds.
Journal of Photochemistry and Photobiology A: Chemistry, 1996
Results are presented on the intramolecular electronic energy transfer (intra-EET) in bichromophoric molecules of the type benzene-adiketone, in which the interchromophore bridge contains methyl substituents/3 to the c~-dicarbonyl acceptor chromophore. These results show that singlet-singlet intra-EET is independent of substitution and can be explained by a model assuming Dexter-type short-range exchange interaction. For singlet-triplet and triplet-triplet transfer, there are indications that the phosphorescence yield of the acceptor is larger than that for non-substituted bichromophoric molecules. This can be explained by through-bond interaction promoting EET via a long-range superexchange mechanism, by variations in the non-radiative decay of the triplet state of the acceptor or by chemical reaction.
Intramolecular energy transfer from a vibronic state in a bichromophoric molecule
Journal of Molecular Structure, 1980
The bichromophoric molecule containing phenanthrene and a-diketone moieties connected by two chains of five methylene groups has been studied. Most spectroscopic properties of this molecule are described by a superposition of those of its constituent chromophores. An extensive study was made of the intramolecular energy transfer process in solution as a function of the excitation frequency and of the sample temperature. It was clearly demonstrated that energy is transferred very efficiently to the a-diketone moiety from a vibronic state of the phenanthrene moiety.
Chemical Physics Letters, 1996
A study of intramolecular electronic energy transfer (Intra-EET) has provided evidence, for the first time, of a dramatic difference in Intra-EET efficiency results obtained under jet cooled and room temperature solution conditions. This was observed with anthracene-(CH2),-naphthalene bichromophoric molecules, A1N (n = 1) and A3N (n = 3). The rich fluorescence excitation spectrum of the naphthalene moiety in AIN indicates an inefficient EET process whose rate constant is substantially slower than that of the naphthalene moiety fluorescence. It was shown that the EET rate depends on a specific vibronic excitation that affects the molecular conformation, and was found to be at least two orders of magnitude slower in AIN molecule compared to A3N.
Theoretical evaluation of the vibronic intensity distribution in the phosphorescence of benzene
1981
The relative intensity of the vibronic components of the phosphorescence spectrum of benzene has been evaiaated theoretically. Ail mechanisms that may be responsible for.the intensity of the most prominent bands have been taken into account and the relevant spin-orbit and vibronic coupling ma&ix elements have been evaluated. In agreement with experimentat findings, it is found that vibronic coupling in the triplet manifold plays the dominant role in indccing the elp bands and that the us band is the most intense. The bfe bands appear to be weak because of substantial canceIlations occurring between large separate contributions. Our results indicate that consideration of all terms and of several intermediate excited states is necessary to obtain a correct picture of phosphorescence of benzene.