Triplet Dexter mechanism

Baldo et al. [ 164] used the platinum complex of 2,3,7,8,12,13,17,18-octaethyl-21 //,23//-porphine (PtOEP, 66) as efficient phosphorescent material. This complex absorbs at 530 nm and exhibits weak fluorescence at 580 nm but strong phosphorescence from the triplet state at 650 nm. Triplet transfer from a host like Alq3 was assumed to follow the Dexter mechanism. Dexter-type excitation transfer is a short-range process involving the exchange of electrons. In contrast to Forster transfer, triplet exciton transfer is allowed. 

The Dexter mechanism can be thought of as electron tunneling, by which one electron from the donor s LUMO moves to the acceptor s LUMO at the same time as an electron from the acceptor s HOMO moves to the donor s HOMO. In this mechanism, both singlet-singlet and triplet-triplet energy transfers are possible. This contrasts with the Forster mechanism, which operates in only singlet states. 

Based on the Dexter mechanism, with a distance-dependent rate coefficient for triplet energy transfer, a non-exponential decay function for donor phosphorescence in a rigid solution was derived... 

We need not be concerned with the quantum mechanical treatment of electron exchange. All we need to know is that triplet energy transfer by electron exchange, the Dexter mechanism, requires appreciable overlap between the molecular orbitals of D and A, so that the critical transfer distance becomes essentially equal to the sum of the van der Waals radii of D and A. 

Triplet-triplet energy transfers in which a - A pair gives D- A can only occur via the Dexter mechanism because orbital overlap is required between... 

In a series of compounds 19, the distance dependency on the energy transfer was inteipreted by the Dexter mechanism [527]. ergy transfer in a supramolec-ular system linked by hydrogen bonds was studied by Harriman et al [635-637] (20-22). Hydrogen bonds were supposed to contribute substantially to through-bond interactions for the triplet energy transfer by the Dexter mechanism. 

---