  The interpretation of nanoplasmonic effects on molecular properties, such as
metal-enhanced absorption or fluorescence, typically assumes a fully coherent
picture (in the quantum-mechanical sense) of the phenomena. Yet, there may be
conditions where the coherent picture breaks down, and decoherence effect
should be accounted for. Using a state-of-the-art multiscale model approach
able to include environment-induced dephasing, here we show that metal
nanoparticle effects on the light absorption by a nearby molecule is strongly
affected (even qualitatively, i.e., suppression vs enhancement) by molecular
electronic decoherence. The present work shows that decoherence can be thought
as a further design element of molecular nanoplasmonic systems.
