Systematic investigation via controlling the energy gap of the local and charge-transfer triplet state for enabling high efficiency thermally activated delayed fluorescence emitters

Yadav, N and Deori, U and Ravindran, E and Sk, B and Rajamalli, P (2023) Systematic investigation via controlling the energy gap of the local and charge-transfer triplet state for enabling high efficiency thermally activated delayed fluorescence emitters. In: Journal of Materials Chemistry C, 11 (46). 16368 -16376.

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Abstract

Thermally activated delayed fluorescence (TADF) emitters have evolved as a certified candidate in light generation technologies for producing efficient organic light-emitting diodes (OLEDs) on account of their 100 internal quantum efficiency (IQE) via reverse intersystem crossing (RISC) and toxic metal-free design. The fast rate of RISC (kRISC) is the ultimate requirement of an efficient TADF emitter, which can be achieved by minimizing the singlet-triplet energy gap (�EST). Here, four donor-acceptor type TADF emitters namely 3BPy-mDCz, 3BPy-mDTA, 3BPy-mDMAC, and 3BPy-mDPT were synthesized based on benzoyl pyridine (3BPy) as an unaltered acceptor and varying the donor strength ranging from carbazole to phenothiazine. These emitters show low �EST values forecasting their TADF nature. The �EST values decreased from 0.22 to 0.14 eV upon increasing the donor strength. The maximum external quantum efficiency (EQE) of 18.7 for 3BPy-mDCz, 22.5 for 3BPy-mDTA, 13.8 for 3BPy-mDMAC and 2.1 for 3BPy-mDPT was obtained. These drastic differences in the performances of 3BPy-mDTA and 3BPy-mDPT are due to the locally excited 3LE(T2) intermediate state between the lowest singlet (S1) and triplet (T1). Among 3BPy-mDMAC and 3BPy-mDPT, the efficiency of 3BPy-mDMAC is superior due to less CT character and high photoluminescence quantum yield (PLQY). This work paves a new direction for efficient TADF molecular design by indicating the role of the intermediate triplet state (3LE) despite possessing high �EST values. © 2023 The Royal Society of Chemistry.

Item Type:	Journal Article
Publication:	Journal of Materials Chemistry C
Publisher:	Royal Society of Chemistry
Additional Information:	The copyright for this article belongs to Royal Society of Chemistry.
Keywords:	Charge transfer; Excited states; Fluorescence; Organic light emitting diodes (OLED); Quantum efficiency; Quantum theory; Synthesis (chemical), Donor strength; Generation technologies; Higher efficiency; Internal quantum efficiency; Intersystem crossing; Light generation; Lightemitting diode; Organic light-emitting; Thermally activated delayed fluorescences; Triplet state, Energy gap
Department/Centre:	Division of Chemical Sciences > Materials Research Centre
Date Deposited:	01 Mar 2024 05:46
Last Modified:	01 Mar 2024 05:46
URI:	https://eprints.iisc.ac.in/id/eprint/83829

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