Time-Resolved Single Molecule Spectroscopy of Conjugated Polymer Nanoparticles

LEE, YOUNG JONG; PALACIOS, RODRIGO E.; BARBARA, PAUL F.

Femtochemistry VII: Fundamental Ultrafast Processes in Chemistry, Physics, and Biology

Elsevier B.V

Lugar: Amsterdam, The Netherlands; Año: 2006; p. 284 - 294

The dynamics of excitons in conjugated polymer materials play a central role in the mechanism of operation of the many important photonic devices based on these materials, including organic light-emitting diodes, photovoltaic solar cells, and sensors [1-8]. The investigation of dynamics of excitons by ensemble time-resolved spectroscopic techniques are limited by the extreme heterogeneity of conjugated polymers. Recently, single molecule spectroscopy (SMS) has proven to be a unique tool for direct measurement of the inhomogeneous spectral distributions of conjugated polymers and for unraveling complex photodynamics involving triplet states, photo-oxidation, and various charge transfer processes that would be extremely difficult to measure by ensemble methods J9-25J. This proceeding summarizes recent breakthroughs in using timeresolved, single molecule spectroscopy to investigate excitons in conjugated polymers. It includes two main topics. First, we use the recently developed technique of microsecond time-scale excitation intensity modulation SMS to study the inhomogeneity in the triplet decay dynamics of the conjugated polymers MEH-PPV at room temperature [16,26]. SeconCi, we report for the first time the use of a femtosecond time-resolved SMS technique to study single exciton dynamics in conjugated polymers. The femtosecond technique monitors the SMS fluorescence as a function of delay between two femtosecond excitation pulses. It achieves both femtosecond time resolution and single molecule sensitivity. It involves the observation of the fluorescence "dip" of single MEH-PPV molecules due to the interaction of singlet excitons through such processes as singlet-singlet (S-S) annihilation, energy transfer, and electron transfer in the single multichromophoric MEH-PPV polymer chains.