  Hybrid organic-inorganic nanomaterials can exhibit transitional behavior that
deviates from models developed for all-organic or all-inorganic materials
systems. Here, we reveal the complexity of exciton-phonon interactions in a
recently discovered 2D layered hybrid organic-inorganic semiconductor, silver
phenylselenolate (AgSePh). Using femtosecond resonant impulsive vibrational
spectroscopy and non-resonant Raman scattering, we measure multiple hybrid
organic-inorganic vibrational modes and identify a subset of these modes that
strongly couple to the electronic excited state. Calculations by density
functional perturbation theory show that these strongly coupled modes exhibit
large out-of-plane silver atomic motions and silver-selenium spacing
displacements. Moreover, analysis of photoluminescence fine-structure splitting
and temperature-dependent peak-shifting/linewidth-broadening suggests that
light emission in AgSePh is most strongly affected by a compound 100 cm-1 mode
involving the wagging motion of phenylselenolate ligands and accompanying
metal-chalcogen stretching. Finally, red-shifting of vibrational modes with
increasing temperature reveals a high degree of anharmonicity arising from
non-covalent interactions between phenyl rings. These findings reveal the
unique effects of hybrid vibrational modes in organic-inorganic semiconductors
and motivate future work aimed at specifically engineering such interactions
through chemical and structural modification.
