Frequency Modulated Femtosecond Stimulated Raman Spectroscopy of Ultrafast Energy Transfer in a Donor–Acceptor Copolymer

Abstract

A Raman-pump frequency modulation scheme and an automated signal-processing algorithm are developed for improved collection of time-resolved femtosecond stimulated Raman spectra. Together, these two advancements remove the broad background signals endemic to FSRS measurements and retrieve signals with high sensitivity. We apply this frequency-modulated femtosecond stimulated Raman spectroscopy (FM-FSRS) to the characterization of ultrafast energy transport in a copolymer comprised of polystyrene linked oligo(phenylene-ethynylene) donor and thiophene-benzothiadiazole acceptor chromophores. After photoexcitation of the donor, ultrafast energy transfer is monitored by the decay of donor vibrational modes and simultaneous growth of acceptor modes. The FM-FSRS method shows clear advantages in signal-to-noise levels, mitigation of artifact features, and ease of data processing over the conventional FSRS technique.