Electronic energy transfer: density of states

Abstract

Intramolecular electronic energy transfer has been observed in one isomer of the bichromophoric molecule D-SpA where the donor (D) is naphthalene, the spacer (Sp) is cyclohexane, and the acceptor (A) is dimethylaniline (DMA). Because the emission spectra of both the donor and acceptor overlap, the emission wavelength could not be used as a diagnostic for energy transfer. However, the donor and acceptor have very different fluorescence lifetimes, and large changes in the fluorescence lifetimes of the vibronic states of naphthalene due to the presence of DMA could be used as a measure of the mixing and energy transfer between the two chromophores. The methyl groups of DMA cause the density of states to rise very rapidly at energies close to the zero-point level, and in the cis isomer this leads to energy transfer from naphthalene vibronic levels that are only slightly above the zero-point level of DMA. The energy-transfer rate was measured as a function of the excited vibronic-state energy. The onset of energy transfer in cis isomers occurs at a lower energy than in the trans isomer, corresponding to a lower density of states.

Intramolecular Triplet Energy Transfer in Flexible Molecules: Electronic, Dynamic, and Structural Aspects

“…Calculations of electronic coupling in rigid systems using ab initio MO theory have revealed that paths involving hops which skip over bonds can make the largest contribution to the total through-bond coupling. 48,49 Equation 4 describes how the quantum yield of energy transfer depends on the three independent kinetic pathways, with χ 3 equaling the percent population of ground-state conformers with the two end chromophores 3-4 Å apart, χ 5 equaling the equilibrium population of conformers with the two end chromophores 5-6 Å apart, k ET 5 equaling the average rate constant for energy transfer by that group of conformers, k rot 5 equaling the average rate constant for rotation by that group of conformers to one with the two ends 3-4 Å apart, χ u equaling the major fraction of the conformers with their ends too far apart to interact, and k ET 3 equaling an average rate constant for these unreactive conformers to rotate irreversibly into ones with their ends 3-4 Å apart. Although k H certainly depends on ketone conformation, its value does not vary much since the geometry near the carbonyl is relatively fixed in alkanophenones of all lengths (Scheme 1).…”

Excitonic splitting and vibronic coupling in 1,2-diphenoxyethane: Conformation-specific effects in the weak coupling limit

“…[15][16][17][18][19][20][21][22][23] The other circumstance in which multiple chromophores exist in close proximity is when they are incorporated as part of the same molecule. Model bichromophores can either be held rigidly in a framework which defines the interchromophore separation and orientation, 24,25 or as part of a flexible linker along which the interchromophore distance and orientation may vary. [26][27][28][29][30][31][32][33][34][35][36][37][38] Flexible linkages offer the tantalizing prospect of studying interchromophore vibronic coupling on a conformation-specific basis under jet-cooled conditions in which population is collisionally cooled into more than one conformational zero-point level.…”

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.…”