Plasmonic Activation of Dark Molecular Transitions Observable in the Far‐Field

ABSTRACT The point‐dipole approximation is commonly applied to simplify light‐matter interactions. As previously reported, it is inaccurate near nanoplasmonic structures as those may strongly enhance higher‐order multipoles. However, the enhancement of higher‐order effects in the far‐field, especially for dipole‐forbidden molecular emitters, remains largely underexplored. In this study, we examine the breakdown of the point‐dipole approximation for light emitted by four molecular systems, with dipole‐allowed and dipole‐forbidden transitions, all near an scanning tunneling microscopy tip‐like plasmonic structure. Importantly, we demonstrate that effects beyond dipolar and quadrupolar orders are observable in both total decay and radiative rates, rendering typically dark molecular systems efficiently fluorescent in the far field. Radiative rates from the nanoplasmonic cavity exceed those of typical dipole‐allowed molecular emitters and are thus predicted as observable in practical experiments.