Triplet migration

The major experimental approaches to detecting triplet migration are ... 

Clearly, this is a simplistic view, since there is a considerable variation in 0g among the PS homopolymers. Yet the excimer fluorescence to fluorescence ratio in DMM solutions is very similar from polymer to polymer. A possible alternative, or additional, route to chain scission may involve intramolecular triplet energy migration and transfer processes. It has been shown (J ) that intramolecular triplet migration is facile in both PS and P(S-alt-MMA), but that sequences of two or more MMA-units interrupt the migration process. If an excited triplet trapping site can release its excess energy without bond scission,... 

Quantitative agreement between theoretical predictions of triplet migration in disordered solids and experiment was shown for an end-capped PF2/6 derivative [163], The time-resolved DF of end-capped PF2/6 was investigated in the form of dense solid films, in dilute frozen solution and in an inert matrix polymer (zeo-... 

In the above study it could be shown that the relaxation of triplets in conjugated polymers is in quantitative agreement with predictions based on the concept of random walk in a disordered solid. Meanwhile, this theoretical framework for the description of migration of triplets in disordered solids has been applied to PFO (polyfluorene with octyl side chains) [168] as well. PFO contains liquid crystalline domains in the polymer that leads to the formation of highly ordered domains (fi phase). This ft phase plays an essential role in the photophysics of this polymer, notably on triplet migration. 

The polyacrylophenones represent another important category of photosensitive polymers. Substitution on the phenyl ring can alter both the efficiency and mechanistic pathway to reaction products (38). Early work (39) showed that the photochemistry could be related to that of small-molecule analogs. Work at the Slovak Academy of Sciences (40) has extended to a very large number of substituted derivatives. In common with other ketone systems, the quantum yields for chain scision are reduced significantly in the solid phase. Some of this is due to the restrictions on molecular mobility, which reduce the quantum yields of type-II photoprocesses. Another important factor is the extensive triplet migration, which, in the solid phase, leads to quenching by reaction products (41), such as the olefin produced by the type-II photoprocess. 

Values of A have been obtained for triplet-triplet migration... 

The earliest quenching studies established that triplet migration occurred, but did not yield any measure of the time-dependent properties of the exciton (e.g. does exciton trapping occur ). If triplet excitons remain mobile throughout their lifetime one would expect the decay rate to be increased at all times by an extrinsic quencher. If trapping occurs one might expect that at later times the decay rate would revert to the "normal"... 

The "polymer effect on (f)g.j. - is it generally true that the intersystem crossing rate is diminished (2) Does triplet migration occur in the fluid phase (3) How does the density of the polymer coil affect triplet quenching or sensitization reactions ... 

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