Differentiation between Shallow and Deep Charge Trap States on Single Poly(3‐hexylthiophene) Chains through Fluorescence Photon Statistics

Abstract

Blinking of the photoluminescence (PL) emitted from individual conjugated polymer chains is one of the central observations made by single-molecule spectroscopy (SMS). Important information, for example regarding excitation energy transfer, can be extracted by evaluating dynamic quenching. However, the nature of trap states, which are responsible for PL quenching, often remains obscured. We present a detailed investigation of the photon statistics of single poly(3-hexylthiophene) (P3HT) chains obtained by SMS. The photon statistics provide a measure of the number and brightness of independently emitting areas on a single chain. These observables can be followed during blinking. A decrease in PL intensity is shown to be correlated with either 1) a decrease in the average brightness of the emitting sites; or 2) a decrease in the number of emitting regions. We attribute these phenomena to the formation of 1) shallow charge traps, which can weakly affect all emitting areas of a single chain at once; and 2) deep traps, which have a strong effect on small regions within the single chains.

Real-time observation of conformational switching in single conjugated polymer chains

“…The random, fast fluctuations observed in class III traces suggest a large number of chromophores undergoing reversible transit to dark states. This behavior has been previously observed and associated with localized charges in single P3HT chains (deep exciton traps) ( 54 ). By contrast, the blinking from more ordered chains exhibiting class II behavior is more likely to be caused by quenching from delocalized charge states (shallow exciton traps).…”

Switching between H- and J-type electronic coupling in single conjugated polymer aggregates

“…The photon statistics are obtained under ambient conditions and with pulsed excitation at a repetition rate of 10 MHz. Only the first second of the acquisition period is taken into account to minimize photo bleaching and blinking effects, which can reduce the quality of photon antibunching 56 , 57 . We measure multiple single aggregates of each material to obtain sufficient photon statistics for the correlation plot.…”

Impact of charge carrier injection on single-chain photophysics of conjugated polymers

“…whether a single charge trap exists or whether multiple quenching sites arise in the multichromophoric system. 20 Generally, the photon statistics of conjugated polymers can be used to estimate the number of independently emitting chromophores under the assumption that the chromophores exhibit the same brightness. 21,22 Intuitively, one would expect that the number of independently emitting chromophores simply decreases during a PL quenching event and that the photon statistics therefore change towards a more non-classical distribution (i.e.…”