Exploiting Transient Anisotropy To Reveal Detailed Molecular-Frame Ultrafast Dynamics

Understanding how energy is transformed on ultrafast time scales is fundamental to the study of photophysics. Transient absorption spectroscopy is widely used to follow these processes, yet the usual "magic-angle" approach superimposes signals with differing polarization in the molecular frame. We employ a simple polarization-resolved method that separates parallel and perpendicular components of molecular-frame transient spectra, revealing otherwise obscured excited-state dynamics. Applied to two chromophore dimers capable of singlet fission, the analysis uncovers orthogonal electronic transitions and clarifies the coupling between monomer units. The molecular-frame spectra exhibit features masked by following the conventional approach, allowing extraction of triplet-pair formation dynamics. This accessible method provides richer insight into excited-state coupling and can be extended to a diverse range of photoactive materials.