Alkyl substituted derivatives of poly(thienylene vinylene) (PTV) have been reported to undergo activated singlet fission at the single molecule level. Our goal is to understand the effect of aggregation on triplet formation and the excited state relaxation in PTV. To accomplish this, we investigate PTV and a heavy atom analog, poly(selenylene vinylene)<b> </b>(PSeV), with ultrafast transient absorption spectroscopy, resonance Raman spectroscopy and time-dependent density functional theory (TD-DFT). The Raman signatures of both PTV and PSeV show strong similarities and both polymers exist as aggregates, even at low concentrations. TD-DFT and time-dependent Raman wavepacket simulations show excellent agreement with the experimental resonance Raman spectrum. Namely, long overtones-combination progressions in both PTV and PSeV Raman spectra indicate large geometrical distortions in the excited state. These results explain the non-emissive nature of PTVs in that the non-radiative rate is very competitive as an excited state relaxation pathway. The presence of aggregate and single-chains in dilute solution obscures the mechanism responsible for efficient triplet formation, making the assignation of spectral signatures to the limiting conformations a challenge.

Aggregation induced vibrational displacements dominate excited state relaxation: Proposed singlet fission active polymers

255th National Meeting (2018)

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