The role of quantum coherence in photochemical functions of molecular systems such as photosynthetic complexes is a broadly debated topic. Coexistence and intermixing of electronic and vibrational coherences has been proposed to be responsible for the observed long-lived coherences and high energy transfer efficiency. However, clear experimental evidence of coherences with different origins operating at the same time has been elusive. In this work, multidimensional spectra obtained from a six-porphyrin nanoring system are analyzed in detail with support from theoretical modeling. We uncover a great diversity of separable electronic, vibrational, and mixed coherences and show their cooperation in shaping the spectroscopic response. The results permit direct assignment of electronic and vibronic states and characterization of the excitation dynamics. The clear disentanglement of coherences in molecules with extended π-conjugation opens up new avenues for exploring coherent phenomena and understanding their importance for the function of complex systems.

It is already well established that the high-frequency intramolecular vibrations are responsible for many observed dynamic phenomena in linear and nonlinear electronic spectroscopy such as the spectral lineshape formation, the transition dipole moment, the lifetime borrowing, and vibrational and mixed coherence beats. All these implications together with the vibronic enhancement of the energy and charge transfer can be explained by the vibronic molecular exciton theory and are highly relevant for the description of the spectral dynamics in photosynthetic pigment-protein complexes. In this paper, a few critical points of the vibronic theory application to linear and nonlinear signals are discussed. Models, which differ in the selection and truncation of molecular basis, are compared by analyzing the energy spectrum and exciton-vibrational dynamics in the presence of the energetic disorder. The limits of the widely used one-particle approximation are defined.