By measuring the fluorescence photon statistics of single chains of a conjugated polymer, we determine the lifetime of the metastable dark state, the triplet exciton. The single molecule emits single photons one at a time, giving rise to photon antibunching. These photons appear bunched in time over longer time scales because of excursions to the triplet dark state. Remarkably, this triplet intermittency in the fluorescence is spontaneously suppressed over time scales of seconds, implying that either triplet formation is inhibited or that triplets are selectively quenched without the singlet fluorescence being affected. Such discrete switching in the strength of photon bunching is only seen in highly ordered and rigid chains of a ladder-type conjugated polymer. It does not occur in single dye molecules. We propose that trapped photogenerated charges on the chain selectively quench triplets but not singlets, presumably because the effective diffusion length of triplets is longer along the highly rigid ladder-type backbone.

中文翻译：

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单共轭聚合物链中三重态激子的动态猝灭。

通过测量共轭聚合物单链的荧光光子统计，我们确定了亚稳态暗态（三重态激子）的寿命。单分子一次发射一个光子，从而引起光子反聚束。由于对三重态暗态的偏移，这些光子在较长的时间尺度上出现了时间上的聚束。值得注意的是，荧光的这种三重态间歇性在数秒的时间范围内被自发抑制，这意味着三重态的形成受到抑制或三重态被选择性淬灭而不会影响单重态荧光。仅在梯型共轭聚合物的高度有序且刚性的链中才能看到这种光子聚集强度的离散转换。它不在单个染料分子中发生。