Some applications of flash techniques

The term triplet state reflects that, since each of the two electrons has a spin quantum number i the spin multiplicity is 1 -I- 2(j -I- j) = 3. 

Triplet states in organic photochemistry. Triplet states are often more important than singlets, and so are important in preparative organic photochemistry. Only a few triplet states, however, can be made in good yield by illumination of the ground state of these, that of biacetyl is the best known. Many other triplet states, however, can be prepared from the ground-state molecules by transfer of electronic energy from biacetyl excited by a flash (see below. Section 4.S.2.2), e.g.  

It is not necessary for the energy-acceptor (anthracene) to absorb light of the frequency used to excite the donor (biacetyl). The process is often called photosensitisation , and the donor a sensitisor , because the acceptor is sensitised by the donor to radiation that it does not absorb [30,b,c]. 

Other non-radiative energy-transfer processes involving triplet states Triplet-triplet energy transfer [37] 

Triplet-triplet annihilation [40]. Since the concentration of excited states in solution is usually small, it follows that encounters between two excited molecules are generally rare. In some circumstances, however, two long-lived triplets (Dj) may collide and give rise to an excited singlet molecule, along with one in the ground state, but no triplet. The overall 

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