Mediated Electronic Energy Transfer: Effect of a Second Acceptor State

Abstract

Intramolecular electronic energy transfer was observed in bichromophoric molecules with the general structure donor-spacer-acceptor where indole is the donor, naphthalene is the acceptor, and cyclohexane is the inert spacer. Measurements were performed in a supersonic jet where both the absorption and emission spectra of the two chromophores were well-resolved and indole could be selectively excited with essentially no excitation on naphthalene. The emission produced on excitation of indole showed strong naphthalene emission and relatively weak indole emission. Moreover, the fluorescence lifetime was similar to the fluorescence lifetime of naphthalene, indicating that the energy transfer occurred on a time scale faster than the fluorescence lifetime of the donor.Energy transfer was observed in several conformers of the bichromophore, but the rates were similar for each. The relative energy-transfer rates of various vibronic levels was determined by measuring the ratio of the naphthalene and indole emission intensities. The energy-transfer rate was found to be fairly constant as a function of vibrational state until the vibrational levels of indole became isoenergetic with the naphthalene S2 state. From this point, the rate increased and then decreased with greater excitation energy. A modification of the theory of mediated intersystem crossing was used to account for this effect.

Hypervalent Ammonium Radicals. Effects of Alkyl Groups and Aromatic Substituents

“…In this case, the electron entering the semioccupied n-orbital at the nitrogen atom recreates the stable molecule in its ground electronic state, whereas electron capture by a distant unoccupied orbital results in the formation of an excited electronic state. The latter corresponds formally to an intramolecular charge-transfer complex whose dissociations may be charge-induced as observed recently for photoexcited aromatic molecules in the gas phase . Another mechanism for de-excitation of charge-transfer complexes is photon emission, as observed for the interaction of anthracene anion radical with triphenylamine cation radical, which resulted in chemiluminescence …”

Photophysics and Mechanisms of Intramolecular Electronic Energy Transfer in Bichromophoric Molecular Systems: Solution and Supersonic Jet Studies

“…A more systematic investigation of intra-EET in isolated bichromophoric molecules was undertaken by Levy and co-workers. ,− Several bichromophoric molecules consisting of two aromatic moieties connected by an aliphatic spacer bridge were studied under jet-cooled conditions. The measurements included excitation and dispersed fluorescence spectra of all bichromophoric molecules, as well as the corresponding spectra of the individual chromophores.…”

Nonadiabaticity and intramolecular electronic energy transfer in the photodissociation of 1-bromo-3-iodopropane at 222 nm

“…Much experimental [1][2][3][4][5][6][7][8] and theoretical [9][10][11] research has focused on describing the radiationless transfer of electronic energy or electronic excitation either from one molecule to another or from one chromophore to another within the same molecule. An elementary theoretical model developed by Förster 12 treats the interaction between the donor and acceptor of electronic excitation as a simple Coulombic interaction, a description which is suited to systems in which the donor and acceptor are well separated spatially.…”

“…Much of the experimental work on the transfer of electronic excitation has been done in condensed phases 4 -7 and has often involved transfer of excitation between different donor and acceptor molecules. [11][12][13] However, some recent work has been done in the gas phase [1][2][3]8 and has concentrated on intramolecular energy transfer, in which the donor and acceptor chromophores are located upon the same molecule.…”