Plasmon enhanced molecular absorption: A mixed quantum-classical description of supramolecular complexes attached to a metal nanoparticle

- Enhancement of molecular absorption was shown for J-aggregate-like coupling between molecules and MNP.
- A large number of molecules is required in order to observe the molecular absorption.
- Pheos Qx-band coupling to the plasmon resonance is hardly observable in the spectrum.

The application of a mixed quantum-classical methodology for an investigation of single pheophorbide-a molecules (Pheos) and respective supramolecular complexes is continued to effects caused by a nearby placed metal nanoparticle (MNP). Therefore, the classical simulation of the molecular nuclear degrees of freedom is combined with a uniform quantum description of the molecular electronic excitations coupled to those of the MNP. To account for the short MNP plasmon life time the quantum dynamics of the electronic degrees of freedom is formulated in the framework of a system-bath theory. Linear absorption spectra are calculated for a spherical 14 nm diameter Au-MNP decorated with isolated Pheos or with P16 complexes formed by 16 Pheos. The spectra are analyzed with respect to the molecular orientation at the MNP surface. While all studies on P16 only account for the Pheo Qy-transition we also present data on the MNP induced change of the single Pheo Qx-absorption.