Energy Transfer In Bichromophoric Molecules Research Articles

Femtosecond Fluorescence Anisotropy Kinetics as a Signature of Ultrafast Electronic Energy Transfer in Bichromophoric Molecules

Ultrafast time resolved fluorescence anisotropy decay measurements were performed to gain insight into the energy gap dependence of donor-acceptor inter-chromophoric coupling within one supra-molecule. Three new compounds, each consisting of two semi-rigidly linked and strongly coupled chromophores, were designed and synthesized for this study. Their general structure is donor-spacer-acceptor, where "donor" is phenylamino, pyrenylamino, or benzanthronylamino moiety, and acceptor is aminobenzanthrone. While being similar structurally, the compounds differ significantly in the excitation energy difference of the two chromophores in a supra-molecule. Experimental data show an ultrafast initial fluorescence emission anisotropy decrease (within less then 1 ps) when the excited state energies of the interacting chromophores are close to each other or equal. No such fast fluorescence anisotropy dynamics is observed for a compound with a large energy gap.

Energy Transfer in Bichromophoric Molecules: The Effect of Symmetry and Donor/Acceptor Energy Gap

The dependence of the rate of singlet excitation transfer on the donor−acceptor energy gap was investigated in bichromophoric spiranes with symmetry-forbidden zero-order electronic coupling. The fluorescence measurements were performed in a supersonic jet in order to avoid collisional and inhomogeneous line broadening. Fluorescence excitation spectra and single-vibronic-level emission spectra of the model chromophores cyclopentaphenanthrene and 1,8-dimethylnaphthalene and the bichromophores spirofluorenephenanthrene and spirofluorenenaphthalene are presented and analyzed. Although the transition moments of the linked chromophores are rigorously perpendicular and the exchange coupling between the v‘ = 0 states is computationally shown to be zero, all spiranes with energy gaps larger than ∼1000 cm-1 exhibited complete electronic energy transfer from all vibrational states of the electronically excited donor, including the undistorted v‘ = 0 state. This behavior is explained in terms of vibronic coupling bet...

Dependence of the intramolecular electronic energy transfer in bichromophoric molecules on the interchromophore bridge

Results are presented on the intramolecular electronic energy transfer (intra-EET) in bichromophoric molecules of the type benzene-α-diketone, in which the interchromophore bridge contains methyl substituents β to the α-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 inteaction 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.

Vibronic coupling and energy transfer in bichromophoric molecules: The effect of symmetry

The fluorescence spectra of a series of bichromophoric molecules consisting of covalently linked fluorene units were investigated in a supersonic jet. In three of the systems (spirobifluorene, d8h8-spirobifluorene and 1-methyl spirobifluorene) no electronic coupling and no corresponding exciton splitting were detected in the zero-point level of the S1 state. Only 9,9′-bifluorene exhibited an exciton splitting in the v=0 state. The lack of coupling was attributed to symmetry; in the spirobifluorenes the planes of the fluorene moieties and the S1←S0 transition moments are perpendicular. When low vibrational levels were excited, state mixing, and energy transfer between the chromophores was observed. This behavior is characteristic of the ‘‘small molecule’’ regime of radiationless transition theory. When higher vibrational levels were excited, the systems exhibited typical ‘‘large molecule’’ behavior. In this limit, both electronic energy transfer, as well as intramolecular vibrational relaxation contribute to the decay of the initially excited state. Intramolecular dispersive interactions were also investigated by comparing the bifluorenes with a series of reference compounds.

Orientational effects in intramolecular electronic energy transfer in bichromophoric molecules II: Triplet-triplet transfer

Intramolecular triplet energy transfer has been investigated in a series of bichromophoric molecules incorporating a cyclic α-diketone and substituted aromatic ring. The distance as well as the relative orientation between the two chromophores varies as a function of the number of methylene groups in the chains joining them. Previous work with these compounds has shown that intramolecular singlet energy transfer between the aromatic and diketone moieties shows a distance dependence which fits with the exchange mechanism. Phosphorescence of the diketone moiety (including temperature dependence) was used to evaluate the efficiency of triplet energy transfer. Direct excitation of the diketone resulted in weak phosphorescence, indicating that intersystem crossing is inefficient. However, excitation of the aromatic moiety resulted in much more intense phosphorescence as a result of the formation of triplet diketone via triplet energy transfer. Complementariness between singlet and triplet energy transfer was evidenced by the fact that some compounds in which singlet energy transfer was more efficient exhibited weaker phosphorescence and vice versa. Quantitative correlations between the triplet energy transfer efficiency and interchromophore distance were not possible.

Orientational effects in intramolecular electronic energy transfer in bichromophoric molecules

A study of intramolecular electronic energy transfer (intra-EET) in a series of bichromophoric molecules, composed of cyclic α-diketones incorporating a para-substituted benzene ring, is reported. The results show that the transfer efficiency is strongly dependent on structure, suggesting that exchange interaction is responsible for intra-EET between close chromophores in a bichromophoric molecule. The relative contributions of interchromophoric distance and orientation of the two chromophores are discussed.

Calculation of the exchange integral for short range intramolecular electronic energy transfer in bichromophoric molecules

A novel calculation of the exchange integral used for describing short range electronic energy transfer (EET) is presented. The calculation is applied to describe intramolecular EET in specially designed bichromophoric molecules. The results indicate that the simple Dexter exponential distance dependence, which is usually assumed to account for short range exchange interaction is valid in some limited cases. However, a more elaborate approach, such as presented here, is required in order to fully describe the molecular geometry effects on short range intramolecular EET.

Molecular electronic energy transfer in bichromophoric molecules in solution and in a supersonic jet expansion

Abstract

The mechanism of short-range intramolecular electronic energy transfer in bichromophoric molecules. 2. Triplet-triplet transfer

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe mechanism of short-range intramolecular electronic energy transfer in bichromophoric molecules. 2. Triplet-triplet transferShammai Speiser, Salah Hassoon, and Mordecai B. RubinCite this: J. Phys. Chem. 1986, 90, 21, 5085–5089Publication Date (Print):October 1, 1986Publication History Published online1 May 2002Published inissue 1 October 1986https://doi.org/10.1021/j100412a041RIGHTS & PERMISSIONSArticle Views250Altmetric-Citations27LEARN 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 (574 KB) Get e-Alerts

Rate of intramolecular electronic energy transfer in coumarin bichromophoric molecules. An investigation by multifrequency phase-modulation fluorometry

Dynamics of intramolecular electronic energy transfer in bichromophoric molecules, consisting of two coumarins linked by a variable number of methylene groups, is investigated by multifrequency phase-modulation fluorometry. From observation of the acceptor delayed emission, information on the rate of transfer can be obtained.

The mechanism of short-range intramolecular electronic energy transfer in bichromophoric molecules

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe mechanism of short-range intramolecular electronic energy transfer in bichromophoric moleculesSalah Hassoon, Hanna Lustig, Mordecai B. Rubin, and Shammai SpeiserCite this: J. Phys. Chem. 1984, 88, 25, 6367–6374Publication Date (Print):December 1, 1984Publication History Published online1 May 2002Published inissue 1 December 1984https://doi.org/10.1021/j150669a063RIGHTS & PERMISSIONSArticle Views264Altmetric-Citations45LEARN 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 (745 KB) Get e-Alerts

Intramolecular electronic energy transfer via exchange interaction in bichromophoric molecules

A theory is presented for intramolecular electronic energy transfer in bichromophoric molecules. Expressions are given for the donor moiety fluorescence (phosphorescence) decay and for its fluorescence (phosphorescence) quantum yield in terms of the average distance between the donor and acceptor moieties and the donor—acceptor bridge flexibility. Comparison with available experimental data supports the predictions of the analysis.