Exciplex, Not Heavy-Atom Effect, Controls the Triplet Dynamics of a Series of Sulfur-Containing Thermally Activated Delayed Fluorescence Molecules.

Autor:	Öner S; Department of Chemistry, Durham University, Stockton Road, Durham DH1 3LE, U.K., Kuila S; Department of Chemistry, Durham University, Stockton Road, Durham DH1 3LE, U.K.; Department of Physics, Durham University, Stockton Road, Durham DH1 3LE, U.K., Stavrou K; Department of Physics, Durham University, Stockton Road, Durham DH1 3LE, U.K., Danos A; Department of Physics, Durham University, Stockton Road, Durham DH1 3LE, U.K., Fox MA; Department of Chemistry, Durham University, Stockton Road, Durham DH1 3LE, U.K., Monkman AP; Department of Physics, Durham University, Stockton Road, Durham DH1 3LE, U.K., Bryce MR; Department of Chemistry, Durham University, Stockton Road, Durham DH1 3LE, U.K.
Jazyk:	angličtina
Zdroj:	Chemistry of materials : a publication of the American Chemical Society [Chem Mater] 2024 Aug 02; Vol. 36 (15), pp. 7135-7150. Date of Electronic Publication: 2024 Aug 02 (Print Publication: 2024).
DOI:	10.1021/acs.chemmater.4c00850
Abstrakt:	The efficiency of thermally activated delayed fluorescence (TADF) in organic materials relies on rapid intersystem crossing rates and fast conversion of triplet (T) excitons into a singlet (S) state. Heavy atoms such as sulfur or selenium are now frequently incorporated into TADF molecular structures to enhance these properties by increased spin-orbit coupling [spin orbit coupling (SOC)] between the T and S states. Here a series of donor-acceptor (D-A) molecules based on 12 H -benzo[4,5]thieno[2,3- a ]carbazole and dicyanopyridine is compared with their nonsulfur control molecules designed to probe such SOC effects. We reveal that unexpected intermolecular interactions of the D-A molecules with carbazole-containing host materials instead serve as the dominant pathway for triplet decay kinetics in these materials. In-depth photophysical and computational studies combined with organic light emitting diode measurements demonstrate that the anticipated heavy-atom effect from sulfur is overshadowed by exciplex formation. Indeed, even the unsubstituted acceptor fragments exhibit pronounced TADF exciplex emission in appropriate carbazole hosts. The intermolecular charge transfer and TADF in these systems are further confirmed by detailed time-dependent density functional theory studies. This work demonstrates that anticipated heavy-atom effects in TADF emitters do not always control or even impact the photophysical and electroluminescence properties. Competing Interests: The authors declare no competing financial interest. (© 2024 The Authors. Published by American Chemical Society.)
Databáze:	MEDLINE
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