Fluorescence decay of quasimonolayered porphyrins near a metal surface separated by short-chain alkanethiols

We investigated the spectral feature and fluorescence lifetime of quasimonolayered porphyrins at very short distance to metal substrates $(1–2.5nm)$ through fine-tuning the length of alkanethiols. The ordered self-assembled monolayers of alkanethiols on Au(111) act as a uniform electronic decoupling layer and suppress the interface quenching via charge transfer. However, the fluorescence quenching via nonradiative energy transfer to the metal still prevails in the porphyrin-alkanethiol-metal sandwich structures. The decay rates are found to follow a $1∕d3$ dependency on spacer thickness, which suggests that the classical electromagnetic theory appears still valid at distance down to $1nm$ through volume damping.