Two-photon excited fluorescence depolarisation and electronic energy migration within donor–donor pairs

Abstract

A unified theoretical description is presented for one- and two-photon excited fluorescence depolarisation and electronic energy migration within pairs of chromophores. Two weakly coupled donor groups are linked via a rigid macromolecule with the ability to undergo restricted reorienting motions. Describing these reorienting motions as well as their influence on the coupling is rather complex, but can be accounted for by using the extended Förster theory. Here explicit expressions have been derived for chromophores belonging to the point groups D(2h), D(2) and C(2v) when residing in uniaxial potentials (i.e. C(infinity v) symmetry). From the given basic equations, it is possible however, to derive the relevant equations for molecules of arbitrary symmetry in any uniaxial orienting potential. The expected time-resolved fluorescence anisotropy for different two-photon absorption tensors are compared for reorienting fluorophores in liquids, as well as in anisotropic systems. Simulated fluorescence depolarisation data are also displayed that mimic energy migration within pairs of two-photon excited donor molecules, which simultaneously undergo reorienting motions within effectively isotropic and uniaxially anisotropic environments. The obtained results demonstrate that the time-resolved fluorescence anisotropy strongly depends on the properties of the two-photon absorption tensor, as well as on using a linear or a circular polarisation of the excitation field.

Membrane Orientation and Lateral Diffusion of BODIPY-Cholesterol as a Function of Probe Structure

“…This is strictly speaking only found in rodlike molecules, such as linear polyenes, where each of the two photons uses a transition moment in the same direction (30,32). The BODIPY moiety belongs to the C 2 molecular symmetry group and therefore has two perpendicular orientations of preferred absorption (33). We found, however, only one dominating orientation in membranes condensed by adding cholesterol, and the cos 4 -function was able to fit the fluorescence response exactly (Fig.…”

A molecular theory for two-photon and three-photon fluorescence polarization

“…An ever-increasing number of studies exploit the advantages inherent in multiphoton excitation, such as the identification of "dark states," 15 photoselection methods, [16][17][18][19][20] and studies on the effects of molecular orientational diffusion [21][22][23] -as well as the opportunities for chemically specific imaging with unprecedented resolution. For simplicity, such experiments are usually performed with a single laser beam, although it has been recognized that the use of two or even three beams with different optical frequencies can offer additional tiers of information.…”

Fluorescence anisotropy: from single molecules to live cells

“…14 For theoretical and experimental details as well as the benefits and applications of 2PA-FA we recommend several recent studies. 3,15,16 In either static or dynamic, single-point or imaging mode, polarization-sensitive detection of fluorescence is a sensitive and versatile tool for the molecular scientist. The key outcome is the derivation of information about the orientation and conformation of macromolecular structures as they evolve during simple binding reactions and more complex biological events.…”