Delayed fluorescence in polymers

Delayed fluorescence consists of an emission identical to the normal or excimer fluorescence as far as the spectral distribution is concerned, but with a longer lifetime. Two main types of delayed fluorescence have been observed. 

With a glassy solution of poly-1-vinylnaphthalene, the delayed emission spectrum has been shown to consist of an emission having a mean lifetime of approximately 80 ms at the normal fluorescence wavelength, in addition to the phosphorescence having a mean lifetime of about 2 s [159]. The delayed fluorescence did not appear in the spectrum of 1-ethylnaphthalene. With the polymer it was found to be inhibited by piperylene, a well-known triplet quencher. These results have been explained by mutual annihilation of two excited triplet states produced by the absorption of two photons by the same polymer molecule. They are considered as strong evidence for migration of the excited triplet state in poly-1-vinylnaphthalene. In polyacenaphthalene, however, which is chemically very similar to poly-1-vinylnaphthalene (see p. 409), no delayed fluorescence could be detected in the same experimental conditions [155]. 

Delayed emission has also been observed for copolymers of -vinyl-naphthalene with styrene and with methyl methacrylate [160,161], and seems to be much more probable with vinylaromatic polymers than with low molecular weight model compounds. This might be the result of extensive energy migration in polymeric systems, although the presence of impurities and structural defects appears likely to be the determining factor in some cases [161]. 

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