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The effect of permanent dipoles on dark states in molecular dimers

The effect of permanent dipoles on dark states in molecular dimers
The effect of permanent dipoles on dark states in molecular dimers

Many organic molecules possess large permanent dipole moments that differ depending on the electronic state. These permanent dipoles influence both intermolecular coupling and interactions with the optical fields, yet they are often neglected in typical theoretical quantum optics treatments. Here, we investigate the optical properties and their effect on dark states of dimers possessing such permanent dipoles. We show that when monomers have excitation-dependent permanent dipoles, optical transitions between the bright and dark states of the dimer are enabled. We investigate how permanent dipoles allow for the existence of static driving terms between the ground and excited states of each monomer. In turn, these can cause the excited states of the monomers to couple indirectly to the zero excitation state of the dimer. This leads to interference between permanent and transition dipoles and can result in the formation of dark states that are entirely localised. Furthermore, dark states formed through indirect coupling exhibit enhanced robustness against energy level fluctuations, which may improve the efficiency of the design of photovoltaic devices.

dark state, molecular dimer, permanent dipole
1367-2630
Freed, Matthew
984c4449-2d36-4519-821e-c8f793d70561
Rouse, Dominic M.
c7afa1bb-c5d8-4fb5-90ad-bacbdc0c67ca
Rocco, Andrea
a9888880-9a03-4c43-8a21-fb15198ef24f
Al-Khalili, Jim
37a6f8b4-3f5d-4e7d-ad8e-44037f429b8d
Florescu, Marian
14b7415d-9dc6-4ebe-a125-289e47648c65
Burgess, Adam
7fe71545-f205-49ea-b066-29c346733cad
Freed, Matthew
984c4449-2d36-4519-821e-c8f793d70561
Rouse, Dominic M.
c7afa1bb-c5d8-4fb5-90ad-bacbdc0c67ca
Rocco, Andrea
a9888880-9a03-4c43-8a21-fb15198ef24f
Al-Khalili, Jim
37a6f8b4-3f5d-4e7d-ad8e-44037f429b8d
Florescu, Marian
14b7415d-9dc6-4ebe-a125-289e47648c65
Burgess, Adam
7fe71545-f205-49ea-b066-29c346733cad

Freed, Matthew, Rouse, Dominic M., Rocco, Andrea, Al-Khalili, Jim, Florescu, Marian and Burgess, Adam (2025) The effect of permanent dipoles on dark states in molecular dimers. New Journal of Physics, 27 (12), [124515]. (doi:10.1088/1367-2630/ae2a61).

Record type: Article

Abstract

Many organic molecules possess large permanent dipole moments that differ depending on the electronic state. These permanent dipoles influence both intermolecular coupling and interactions with the optical fields, yet they are often neglected in typical theoretical quantum optics treatments. Here, we investigate the optical properties and their effect on dark states of dimers possessing such permanent dipoles. We show that when monomers have excitation-dependent permanent dipoles, optical transitions between the bright and dark states of the dimer are enabled. We investigate how permanent dipoles allow for the existence of static driving terms between the ground and excited states of each monomer. In turn, these can cause the excited states of the monomers to couple indirectly to the zero excitation state of the dimer. This leads to interference between permanent and transition dipoles and can result in the formation of dark states that are entirely localised. Furthermore, dark states formed through indirect coupling exhibit enhanced robustness against energy level fluctuations, which may improve the efficiency of the design of photovoltaic devices.

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Accepted/In Press date: 8 December 2025
e-pub ahead of print date: 24 December 2025
Published date: 24 December 2025
Keywords: dark state, molecular dimer, permanent dipole

Identifiers

Local EPrints ID: 512291
URI: http://eprints.soton.ac.uk/id/eprint/512291
ISSN: 1367-2630
PURE UUID: 8dc8483e-7537-423a-8b45-bd690bbc5a72
ORCID for Marian Florescu: ORCID iD orcid.org/0000-0001-6278-9164

Catalogue record

Date deposited: 23 Jun 2026 17:13
Last modified: 17 Aug 2026 05:20

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Contributors

Author: Matthew Freed
Author: Dominic M. Rouse
Author: Andrea Rocco
Author: Jim Al-Khalili
Author: Marian Florescu ORCID iD
Author: Adam Burgess

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