In a new experiment, Greg Engel and his colleagues found that groups of chlorophyll molecules spend a surprisingly long time in a so-called superposition of states--a quantum phenomenon in which many molecules share excitation energy
and so are simultaneously excited and relaxed.
The excited donor (D*) can relax either by re-emission of a photon or by transferring its excitation energy
to a nearby acceptor (A) to produce an excited acceptor state (A*).
interference from urine matrix attributable to absorbance of excitation energy
, we observed that urine samples absorbed the excitation energy
at 340 nm to various degrees (Table 4).
Once excited, these molecules generally lose about 10% of their excitation energy
The results demonstrate: (1) conversion of excess excitation energy
into heat, called thermal dissipation, limits energy flux through photosystem (PS) II during development of PS II, (2) following development of maximum electron-transport potential within PS II, thermal dissipation decreases allowing for increased photochemical utilization of excitation energy
, and (3) changes of the magnitude of thermal dissipation help maintain an optimal, manageable energy flux through the photosystems during the development of photochemistry.
In biophysics, for example, this process defines the migration of excitation energy
within photosynthetic systems (commonly the Frster mechanism).
Quantum coherence is likely to be involved in not only the first ultrafast stages of excitation energy
transfer in the photosynthetic light harvesting antenna but also in the charge separation process in the photosynthetic reaction center by coupling to specific vibrational states of this pigment-protein complex (Romero et al, Nature Physics 10, 676-682, 2014) .
Looking in turn at principles, techniques, and applications, they consider such topics as characteristics of fluorescence emission, environmental effects on fluorescence emission, excitation energy
transfer, time-resolved fluorescence techniques, evaluating local physical parameters with fluorescent probes, and autofluorescence and fluorescence labeling in biology and medicine.
The PWB cross sections are calculated from uncorrelated wave functions, and the scaling requires only the binding energy B of the bound electron that is excited, the excitation energy
E, and an accurate dipole oscillator strength f for the transition.
of the change in the distribution of excitation energy
between the two
3+] and rhodamine is short enough to allow excitation energy
to be transferred from [Tb.
with subsequent relaxation of nuclear excitation energy