Symmetry-breaking charge-separation in a subphthalocyanine dimer resolved by two-dimensional electronic spectroscopy

Understanding the role of structural and environmental dynamics in the excited state properties of strongly coupled chromophores is of paramount importance in molecular photonics. Ultrafast, coherent and multidimensional spectroscopies have been utilised to investigate such dynamics in the simplest model system, the molecular dimer. Here we present a half-broadband two-dimensional electronic spectroscopy (HB-2DES) study of the previously reported ultrafast symmetry-breaking charge separation (SB-CS) in the subphthalocyanine oxo-bridged homodimer μ-OSubPc2. Electronic structure calculations and 2D cross-peaks reveal the dimer’s excitonic structure, whilst ultrafast evolution of the multidimensional spectra unveils subtle features of structural relaxation, solvation dynamics and inhomogeneous broadening in the SB-CS. Analysis of coherently excited vibrational motions reveals dimer specific low frequency Raman active modes coupled to higher frequency vibrations localised on the SubPc cores. Finally, beatmap amplitude distributions characteristic of excitonic dimers with multiple bright states are reported and analysed.