The optical properties of conjugated polymer films vary substantially with morphology and this has material consequences for the design of optoelectronic devices based on these materials. We systematically vary morphology at the single chain level to illustrate the interplay between energy transfer amongst and aggregation of chromophores in determining the photophysics. We examine photoluminescence in the extreme cases of highly collapsed and of extended polymer chains. In the former situation, the polymer behaves approximately like many independent chromophores while in the latter strong energy funneling to single chromophores is observed such that very large chains (~ 500 KD) can behave much like single dye molecules. Of greatest interest is the intermediate case where surprising and instructive phenomena are observed that cannot be explained in the context of previous literature pictures. In particular, we show that in some cases it is possible to greatly enhance the chain emission by introduction of oxygen that results in deliberate photooxidation of low energy but poorly emitting chromophores. This leads to other interesting phenomena such as “flaring” where short, intense luminescence spikes are observed. We also infer the existence of a set of nearly invisible chromophores that can play a large role in the overall chain photophysics and propose a model distinct from the conventional picture that explains our observations.

Single chain studies of exciton migration and identity in conjugated polymers

256th National Meeting (2018)

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