Solution-based single molecule imaging of surface-immobilized conjugated polymers.

The photophysical behavior of conjugated polymers used in modern optoelectronic devices is strongly influenced by their structural dynamics and conformational heterogeneity, both of which are dependent on solvent properties. Single molecule studies of these polymer systems embedded in a host matrix have proven to be very powerful to investigate the fundamental fluorescent properties. However, such studies lack the possibility of examining the relationship between conformational dynamics and photophysical response in solution, which is the phase from which films for devices are deposited. By developing a synthetic strategy to incorporate a biotin moiety as a surface attachment point at one end of a polyalkylthiophene, we immobilize it, enabling us to make the first single molecule fluorescence measurements of conjugated polymers for long periods of time in solution. We identify fluctuation patterns in the fluorescence signal that can be rationalized in terms of photobleaching and stochastic transitions to reversible dark states. Moreover, by using the advantages of solution-based imaging, we demonstrate that the addition of oxygen scavengers improves optical stability by significantly decreasing the photobleaching rates.