Collective States in Molecular Monolayers on 2D Materials

Area of Science:

• Condensed Matter Physics
• Materials Science
• Organic Electronics

Background:

• Collective excited states arise in 2D organic layers via Coulomb coupling of molecular dipoles.
• These states appear as distinct, low-energy peaks in optical spectra, differing from monomer transitions.
• Real-world molecular monolayers exhibit disorder and broadening, affecting collective state properties.

Purpose of the Study:

• Investigate the robustness of collective states against disorder and broadening.
• Analyze the optical response of organic monolayers on different 2D substrates.
• Understand the transition from localized molecular states to delocalized collective states.

Main Methods:

• Microscopic modeling of 2D dipole lattices to calculate collective state properties and spectra.
• Experimental measurement of optical absorption and luminescence of MePTCDI monolayers.
• Multiwavelength Raman scattering to analyze molecular states on hexagonal boron nitride and graphene.

Main Results:

• Collective states persist with 1-10% variation in molecular position and transition frequency.
• MePTCDI on hexagonal boron nitride shows strong collective state emission, limited by inhomogeneous broadening.
• Luminescence is quenched on graphene due to nonradiative excitation transfer, despite similar collective state formation.

Conclusions:

• Collective states in organic monolayers are robust against spatial and frequency disorder.
• Substrate choice significantly impacts collective state emission due to energy transfer mechanisms.
• Organic monolayers exhibit promising properties for soft-matter optoelectronics.