Gauging Molecular Interactions between Substrates and Adsorbates. Substrate Mediation of Surface-Bound Chromophore Vibronic Coupling

We have studied the steady-state and time-resolved optical response of substituted pyrene chromophores in solution and tethered to dielectric, doped semiconductor, and metallic substrates. The steady-state spectra of the substituted pyrenes indicate that both the S2 ← S0 and S1 ← S0 transitions play significant roles in the measured optical response. In solution, time-resolved measurements of the substituted pyrene chromophores reveal a zero-time anisotropy that depends on the identity of the substituent. We attribute this phenomenon to intramolecular interactions between the pyrene chromophore and the substituent. For chromophores bound to substrates, we find that there is no discernible motion on the nanosecond time scale and that the measured zero-time anisotropy depends on the identity of the substrate. The interactions between the chromophore and the substrate are manifested as the mediation of S1−S2 vibronic coupling in the chromophore.