Differentiation between shallow and deep charge trap states on single poly(3-hexylthiophene) chains through fluorescence photon statistics

TL;DR

This study uses photon statistics from single-molecule spectroscopy to distinguish shallow and deep charge trap states in conjugated polymer chains, revealing their distinct effects on photoluminescence blinking behavior.

Contribution

It introduces a novel approach to differentiate trap states in conjugated polymers using fluorescence photon statistics during blinking analysis.

Findings

Shallow traps cause a uniform decrease in brightness across the chain.

Deep traps lead to localized quenching in small regions.

Photon statistics effectively distinguish between trap types.

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, e.g., 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 (i) a decrease in the average brightness of the emitting sites; or (ii) a decrease in the number of emitting regions. We attribute these phenomena to the formation of (i) shallow charge traps, which can weakly affect all emitting areas of a single chain at once; and (ii) deep traps, which have a strong effect on small regions within the single chains.