Direct Observation of Ultrafast Singlet Exciton Fission in Three Dimensions

Abstract

We present quantitative ultrafast interferometric pump-probe microscopy capable of tracking of photoexcitations with sub 10 nm spatial precision in three dimensions with 15 fs temporal resolution, through retrieval of the full transient photoinduced complex refractive index. We use this methodology to study the spatiotemporal dynamics of the quantum coherent photophysical process of ultrafast singlet exciton fission. Measurements on microcrystalline pentacene films grown on glass (SiO${}_2$) and boron nitride (hBN) reveal a 25 nm, 70 fs expansion of the joint-density-of-states along the crystal a,c-axes accompanied by a 6 nm, 115 fs change in the exciton density along the crystal b-axis. We propose that photogenerated singlet excitons expand along the direction of maximal orbital $\pi$-overlap in the crystal a,c-plane to form correlated triplet pairs, which subsequently electronically decouples into free triplets along the crystal b-axis due to molecular sliding motion of neighbouring pentacene molecules. This methodology opens a new route for the study of three dimensional transport on ultrafast timescales.

References in corpus (11)

• Femtosecond Coherence and Quantum Control of Single Molecules at Room Temperature
• The point spread function in interferometric scattering microscopy (iSCAT). I. Aberrations in defocusing and axial localization
• Singlet fission for quantum information and quantum computing: The parallel JDE model
• Origins of singlet fission in solid pentacene from an ab initio Green's-function approach
• Ultrafast Tracking of Exciton and Charge Carrier Transport in Optoelectronic Materials on the Nanometer Scale
• The impact of exciton delocalization on exciton-vibration interactions in organic semiconductors
• Nuclear dynamics of singlet exciton fission: a direct observation in pentacene single crystals
• Imaging the coherent propagation of collective modes in the excitonic insulator candidate Ta${}_2$NiSe${}_5$ at room temperature
• Extracting Quantitative Dielectric Properties from Pump-Probe Spectroscopy
• Unconventional light-induced states visualized by ultrafast electron diffraction and microscopy
• Three-dimensional structure from single two-dimensional diffraction intensity measurement

Cited by in corpus (2)

• Local Symmetry Breaking Drives Picosecond Spin Domain Formation in Polycrystalline Semiconducting Films
• Topologically-enhanced exciton transport