Single Molecule Modulation Spectroscopy of Conjugated Polymers

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Abstract
This paper describes a new single molecule spectroscopy approach for the investigation of triplet−triplet and singlet−triplet interactions in conjugated polymers. The technique involves the irradiation of isolated single, mulitchromophoric, conjugated polymer molecules by a repetitive sequence of variable-intensity microsecond time scale excitation pulses. The fluorescence intensity is synchronously time-averaged for thousands of cycles of the pulse sequence to yield a high signal-to-noise fluorescence transient on the microsecond time scale. The transient can be analyzed with kinetic models to obtain quantitative information about the kinetics of triplet−triplet exciton annihilation and the quenching of singlet excitons by triplet excitons in conjugated polymers.