Lowering of the singlet-triplet energy gap via intramolecular exciton-exciton coupling

• Published in: Nature communications Vol. 15; no. 1; pp. 8705 - 10
• Main Authors: Schäfer, Clara, Ringström, Rasmus, Hanrieder, Jörg, Rahm, Martin, Albinsson, Bo, Börjesson, Karl
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 08.10.2024; Nature Publishing Group; Nature Portfolio
• Subjects: 140/125; 639/301/299/890; 639/638/439/890; 639/638/440/527; 639/638/440/949; Atomic energy levels; Coupling; Design factors; Dipole moments; Emitters; Energy; Energy gap; Excitation; Excitons; Humanities and Social Sciences; multidisciplinary; Organic Chemistry; Organic light emitting diodes; Organisk kemi; Science; Science (multidisciplinary); Triplet state
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-53122-7

Organic dyes typically have electronically excited states of both singlet and triplet multiplicity. Controlling the energy difference between these states is a key factor for making efficient organic light emitting diodes and triplet sensitizers, which fulfill essential functions in chemistry, physics, and medicine. Here, we propose a strategy to shift the singlet excited state of a known sensitizer to lower energies without shifting the energy of the triplet state, thus without compromising the ability of the sensitizer to do work. We covalently connect two to four sensitizers in such a way that their transition dipole moments are aligned in a head-to-tail fashion, but, through steric encumbrance, the delocalization is minimized between each moiety. Exciton coupling between the singlet excited states considerably lowers the first excited singlet state energy. However, the energy of the lowest triplet excited state is unperturbed because the exciton coupling strength depends on the magnitude of the transition dipole moments, which for triplets are very small. We expect that the presented strategy of designed intramolecular exciton coupling will be a useful concept in the design of both photosensitizers and emitters for organic light emitting diodes as both benefits from a small singlet-triplet energy gap. Controlling energetics is a key factor for efficient organic light emitting diodes and triplet sensitizers. Here, the authors use intramolecular exciton coupling to selectively lower the energy of a singlet state without perturbing the triplet state.