Two-dimensional Electronic Spectroscopy with White Light: From Photosynthetic Nanotubes to Singlet Fission Dimers

Two-dimensional electronic spectroscopy (2DES) resolves energy and charge transfer dynamics with femtosecond (fs) temporal resolution along multiple spectral dimensions – excitation, emission and coherence axes. Repetition-rate scalability while maintaining temporal and spectral resolution is the ideal route towards extending 2DES for imaging applications.
Here we describe a pump-probe 2D spectrometer^1,2 that takes a white light continuum (WLC) input for both pump and probe and detects shot-to-shot 2D spectra in a repetition rate scalable manner without sacrificing spectral resolution or bandwidth. The throughput and sensitivity of this approach at 100 kHz repetition rate is better than the state-of-the-art AOM pulse shaping approaches, with >200 nm pump and probe bandwidths and sub-10 fs temporal resolution.
Further introducing the additional knob of polarization-control³ allows us to decipher the presence of strong intraband couplings within the overlapping vibrational-electronic (vibronic) bands of light harvesting nanotubes that close mimic the naturally occurring chlorosome photosynthetic antennas. These observations suggest that vibronic couplings may indeed survive at room temperature in large aggregates to drive ultrafast internal conversion.
We also demonstrate applications of WLC-2DES approach to multiple families of singlet fission dimers³, where we find spectral signatures such as a higher energy 2D cross-peak and heterogeneous singlet fission at only certain conformations accompanied by fast changes in the electronic transition dipole orientations. Together these observations improve our mechanistic understanding of the first steps of intramolecular singlet fission and inform rational design of singlet fission materials.
References:
1. Bhat VN, Thomas AS, Bhattacharyya A, Tiwari V. Rapid scan white light pump-probe spectroscopy with 100 kHz shot-to-shot detection. Opt Contin. 2023;2(9):1981-1995. doi:10.1364/OPTCON.496928
2. Thomas AS, Bhat VN, Tiwari V. Rapid scan white light two-dimensional electronic spectroscopy with 100 kHz shot-to-shot detection. J Chem Phys. 2023;159(24):244202. doi:10.1063/5.0179474
3. Bhattacharyya A, Sahu A, Patra S, Tiwari V. Low- and high-frequency vibrations synergistically enhance singlet exciton fission through robust vibronic resonances. Proc Natl Acad Sci. 2023;120(49):e2310124120. doi:10.1073/pnas.2310124120