UV-visible spectroscopy and fluorescence analysis of polymer reactions

8 UV-visible spectroscopy and fluorescence analysis of polymer reactions 

The use of electronic spectroscopy to follow polymer reactions has been limited because of the broad spectra resulting from electronic transitions and the lack of molecular structural information in the spectra. The only exception to this is in polymer photochemistry, where information regarding the excited states and the pathways for energy loss may be exploited 

In the situation described as Stem-Volmer quenching, the fluorescence quantum yield is reduced to in the presence of Q, a quenching molecule of concentration [Q], 

In solution the quenching rate coefficient will be the diffusion-controlled rate coefficient for encounter, Ar, which is related to the viscosity rj by the Debye equation  

Excimer emission is a broad structureless emission red-shifted from the normal fluorescence and is observed at high chromophore concentration because it requires close encounter of the excited and the unexcited molecule to form the encounter complex (SjSq) with a separation of 3 A This will depend on the encounter occurring during the lifetime of the excited state so that, as the viscosity increases, there will be a decrease in the intensity of excimer emission. This is discussed and an example shown in Section 3.3.8. 

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