Strong Coupling Between Plasmons and Molecular Excitons in Metal–Organic Frameworks

Abstract

This Letter describes strong coupling of densely packed molecular emitters in metal−organic frameworks (MOFs) and plasmonic nanoparticle (NP) lattices. Porphyrin-derived ligands with small transition dipole moments in an ordered MOF film were grown on Ag NP arrays. Angle-resolved optical measurements of the MOF-NP lattice system showed the formation of a polariton that is lower in energy and does not cross the uncoupled MOF Q 1 band. Modeling predicted the upper polariton energy and a calculated Rabi splitting of 110 meV. The coupling strength was systematically controlled by detuning the plasmon energy by changing the refractive index of the solvents infiltrating the MOF pores. Through transient absorption spectroscopy, we found that the lower polariton decays quickly at shorter time scales (<500 ps) and slowly at longer times because of energy transfer from the upper polariton. This hybrid system demonstrates how MOFs can function as an accessible excitonic material for polariton chemistry.

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

“…First, we define effective polarizabilities ,eff α νν ′ by inverting Equation ( 3) with eff T on the left-hand side. We then have that: (20) where is the unit 3 × 3 matrix, and ρ the concentration of the molecules.…”

“…[ 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. [ 21 ]…”

Dipole-mediated exciton management strategy enabled by reticular chemistry

“…Owing to their rigid structures that place organic ligands at welldefined distances and angles from each other, metal-organic frameworks (MOFs) have recently gained traction as platforms for controlling excitons. [12][13][14][15][16][17][18][19][20][21][22][23] One MOF topology that allows perpendicular arrangement of donor and acceptor moieties at close distance is a square lattice defined by dinuclear metal paddlewheel tetracarboxylates with rectangular ligands, pillared by a second type of ligand, typically linear bipyridyl molecules (Fig. 2).…”

Connecting the Dots for Fundamental Understanding of Structure-Photophysics-Property Relationships of COFs, MOFs, and Perovskites using a Multiparticle Holstein Formalism

“…Excited state processes of technologically relevant organic and hybrid materials such as polymers, COFs, MOFs, and perovskites are mainly governed by the quantum mechanical behavior of mobile quasiparticles, such as Frenkel, charge-transfer, and Wannier-Mott excitons, polarons and bipolarons, trions, and the interaction of these quasiparticles with intra-and inter-molecular vibrational modes. [129][130][131][132][133][134][135][136][137][138][139][140][141][142][143][144] These vibronic effects, which arise from the coupling of electronic transitions with the nuclear vibrational motion, play a central role in determining the photophysical response of organic 145,[145][146][147] and hybrid materials [148][149][150][151][152][153][154] as well as excited state dynamics in chemical and biological systems. [155][156][157][158][159][160][161][161][162][163] It is therefore not surprising that any progress in the design of novel materials warrants a robust theoretical methodology that can provide an in-depth understanding of how the complicated interplay between photons, excitons, polarons, bipolarons, phonons, and spins influences the photoinduced excited state processes of a wide range of materials.…”