The Role of Molecular Arrangement on the Strongly Coupled Exciton–Plasmon Polariton Dispersion in Metal–Organic Hybrid Structures

Abstract

Metal−organic hybrid structures have been demonstrated to be a versatile platform to study primary aspects of light−matter interaction by means of emerging states comprising excitonic and plasmonic properties. Here we are studying the wave-vector-dependent photoexcitations in gold layers covered by molecular films of zinc phthalocyanine and its fluorinated derivatives (F n ZnPc, with n = 0, 4, 8, 16). These layered metal−organic samples show up to four anticrossings in their dispersions correlating in energy with the respective degree of ZnPc fluorination. By means of complementary structural and theoretical data, we attribute the observed anticrossings to three main scenarios of surface plasmon coupling: (i) to aggregated α-phase regions within the F n ZnPc layers at 1.75 and 1.85 eV, (ii) to a coexisting F 16 ZnPc β-polymorph at 1.51 eV, and (iii) to monomers, preferentially located at the metal interface, at 2.15 eV. Whereas energy and splitting of the monomer anticrossings depend on strength and average tilting of the molecular dipole moments, the aggregaterelated anticrossings show a distinct variation with degree of fluorination. These observations can be consistently explained by a change in F n ZnPc dipole density induced by an increased lattice spacing due to the larger molecular van der Waals radii upon fluorination. The reported results prove Au/F n ZnPc bilayers a model system to demonstrate the high sensitivity of exciton−plasmon coupling on the molecular alignment at microscopic length scales.

A Multi‐Scale Approach for Modeling the Optical Response of Molecular Materials Inside Cavities

“…The cavity modes are yet another degree of freedom amenable to optimization beyond Fabry‐Perot configurations, [ 6–8 ] and, when the interaction is strong enough, hybrid light‐matter modes known as polaritons will form inside the cavity: The optical properties of the joint system can differ significantly from the separate responses of cavity and materials. [ 10–19 ] The choice of MOFs as active materials inside the cavities is motivated by the crystallinity and porosity of this class of reticular compounds, which makes possible a straightforward experimental characterization using X‐ray diffraction methods as well as a tuning of the dielectric constant inside the cavity by loading the MOFs with small molecules. Hybrid light‐matter states have also been observed in MOFs placed on a plasmonic nanoparticle lattice [ 20 ] and even in molecular films on top of substrates.…”

Exploring Functional Photonic Devices made from a Chiral Metal-Organic Framework Material by a Multiscale Computational Method

“…Furthermore, it is also possible to load achiral MOFs with chiral guest structures [20]. The exciting opportunity to control the chirality of highly porous structured materials [21,22] intrigued researchers to explore applications in the fields of enantioselective chemistry and catalysis [23][24][25], chiral molecules separation [26,27], optics [17,[28][29][30][31][32][33][34][35], and sensors based on chiral MOFs [36][37][38][39][40].…”

Strong light–matter coupling in pentacene thin films on plasmonic arrays

“…11,39,40 Furthermore, investigations on coupling in polycrystalline thin films are in general very rare due to the additional interfering parameters of intermolecular interactions and disorder. 41 Yet, for device applications thin films are of major importance. 42…”

“…11,39,40 Furthermore, investigations on coupling in polycrystalline thin films are in general very rare due to the additional interfering parameters of intermolecular interactions and disorder. 41 Yet, for device applications thin films are of major importance. 42 In this work, we used pentacene (PEN) thin films as organic material on open nanoparticle cavities, since PEN is a prototypical organic semiconductor and SF material.…”