Ru(II) polypyridine complexes: photophysics, photochemistry, eletrochemistry, and chemiluminescence

When a molecule absorbs a photon of appropriate energy, a chain of photophysical events ensues, such as internal conversion or vibrational relaxation (loss of energy in the absence of light emission), fluorescence, intersystem crossing (from singlet state to a triplet state) and phosphorescence, as shown in the Jablonski diagram for organic molecules (Fig. 1). Each of the processes occurs with a certain probability, characterized by decay rate constants (k). It can be shown that the average length of time τ for the set of molecules to decay from one state to another is reciprocally proportional to the rate of decay: τ = 1/k. This average length of time is called the mean lifetime, or simply lifetime. It can also be shown that the lifetime of a photophysical process is the time required by a population of N electronically excited molecules to be reduced by a factor of e. Correspondingly, the fluorescence lifetime is the time required by a population of excited fluorophores to decrease exponentially to N/e via the loss of energy through fluorescence and other non-radiative processes. The lifetime of photophycal processes vary significantly from tens of femotoseconds for internal conversion1,2 to nanoseconds for fluorescence and microseconds or seconds for phosphorescence.1






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Figure 1


Jablonski diagram and a timescale of photophysical processes for organic molecules.

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Fluorescence Lifetime Measurements and Biological Imaging

This Review covers recent progress on near-infrared fluorescence imaging for preclinical animal studies and clinical diagnostics and interventions.

Near-infrared fluorophores for biomedical imaging

Mise au point. Theorie des effets de couplage vibronique multimodes. Probleme a 2 etats. Couplage vibronique mettant en jeu des modes et des etats degeneres. Effets du couplage vibronique multimodes en spectroscopie. Comportement statistique des niveaux d'energie vibroniques. Intersections coniques et evolution temporelle de la fluorescence

Multimode molecular dynamics beyond the Born-Oppenheimer approximation

This is an overview of some of the important, challenging, and problematic issues in contemporary electron transfer research. After a qualitative discussion of electron transfer, its time and distance scales, energy curves, and basic parabolic energy models are introduced to define the electron transfer process. Application of transition state theory leads to the standard Marcus formulation of electron transfer rate constants. Electron transfer in solution is coupled to solvent polarization effects, and relaxation processes can contribute to and even control electron transfer. The inverted region, in which electron transfer rate constants decrease with increasing exoergicity, is one of the most striking phenomena in electron transfer chemistry. It is predicted by both semiclassical and quantum mechanical models, with the latter appropriate if there are coupled high- or medium-frequency vibrations. The intramolecular reorganizational energy has different contributions from different vibrational modes, whic...

Contemporary Issues in Electron Transfer Research

In this paper we present a unified treatment of non-radiative decay processes in large molecules which involve either electronic relaxation between two electronic states or unimolecular rearrangeme...

The energy gap law for radiationless transitions in large molecules

This work considers the adiabatic-diabatic transformation for electronic states and the diabatic representation which follows accordingly. Two cases where ambiguity is encountered are discussed: one is the case where the reduced electronic manifold is not well separated everywhere in configuration space and the other is the case of conical intersections exemplified by the E ⊗ e Jahn-Teller situation. It is shown that in both cases well defined diabatic states can be formed in most regions of configuration space.

Robert Englman

Papers

The energy gap law for radiationless transitions in large molecules

A study of the diabatic electronic representation within the Born-Oppenheimer approximation

Jahn—Teller Effect on a Triplet due to Threefold Degenerate Vibrations

The energy gap law for non-radiative decay in large molecules

A modified Born-Oppenheimer equation: application to conical intersections and other types of singularities