Time-Resolved Raman Spectroscopy of Polaron Pair Formation in Poly(3-hexylthiophene) Aggregates.
The ultrafast formation of bound charge pairs, or polaron pairs (PPs), in mixed-order aggregates of poly(3-hexylthiophene) was investigated using femtosecond stimulated Raman spectroscopy (FSRS). Spectral dynamics in the carbon-carbon stretching region reveal a significant photoinduced depletion in steady-state features associated with lamellar-stacked, ordered polymer regions upon 500 nm photoexcitation; this is followed by the appearance of red-shifted features attributable to PPs that is delayed by a few hundred femtoseconds. PP features decay with concomitant recovery of the steady-state Raman depletion over a few picoseconds. The vibrational spectrum of the PP obtained exhibits a modest red shift (<15 cm(-1)) and lower Raman activity relative to steady-state features in the C═C stretching region but similar features in other regions. In total, this work demonstrates the potential of time-resolved Raman as a morphologically selective and structurally sensitive probe for tracking ultrafast charge separation and recombination dynamics within polymer regions of conjugated materials.
Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States.
Timothy J
TJ
Magnanelli
Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States.
Arthur E
AE
Bragg
FSRS; P3HT; Raman; conjugated polymer; dynamics; morphology; polaron pairs