  Hybrid organic-inorganic semiconductors feature complex lattice dynamics due
to the ionic character of the crystal and the softness arising from
non-covalent bonds between molecular moieties and the inorganic network. Here
we establish that such dynamic structural complexity in a prototypical
two-dimensional lead iodide perovskite gives rise to the coexistence of diverse
excitonic resonances, each with a distinct degree of polaronic character. By
means of high-resolution resonant impulsive stimulated Raman spectroscopy, we
identify vibrational wavepacket dynamics that evolve along different
configurational coordinates for distinct excitons and photocarriers. Employing
density functional theory calculations, we assign the observed coherent
vibrational modes to various low-frequency ($\lesssim 50$\,cm$^{-1}$) optical
phonons involving motion in the lead-iodide layers. We thus conclude that
different excitons induce specific lattice reorganizations, which are
signatures of polaronic binding. This insight on the energetic/configurational
landscape involving globally neutral primary photoexcitations may be relevant
to a broader class of emerging hybrid semiconductor materials.
