Schäfer Clara, Ringström Rasmus, Hanrieder Jörg, Rahm Martin, Albinsson Bo, Börjesson Karl
Department of Chemistry and Molecular Biology, University of Gothenburg, Box 462, 405 30, Gothenburg, Sweden.
Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Kemivägen 10, 412 96, Gothenburg, Sweden.
Nat Commun. 2024 Oct 8;15(1):8705. 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.
有机染料通常具有单重态和三重态多重性的电子激发态。控制这些态之间的能量差是制造高效有机发光二极管和三重态敏化剂的关键因素，这些器件在化学、物理和医学中发挥着重要作用。在此，我们提出一种策略，在不改变三重态能量的情况下，将已知敏化剂的单重激发态转移到更低能量，从而不影响敏化剂的做功能力。我们以这样一种方式共价连接两到四个敏化剂，使得它们的跃迁偶极矩以头对尾的方式排列，但是，通过空间位阻，每个部分之间的离域作用最小化。单重激发态之间的激子耦合显著降低了第一激发单重态能量。然而，最低三重激发态的能量不受影响，因为激子耦合强度取决于跃迁偶极矩的大小，而对于三重态来说跃迁偶极矩非常小。我们预计，所提出的设计分子内激子耦合策略将是设计用于有机发光二极管的光敏剂和发光体的一个有用概念，因为两者都受益于较小的单重态 - 三重态能隙。
