Issue 28, 2024

Fast, efficient, narrowband room-temperature phosphorescence from metal-free 1,2-diketones: rational design and the mechanism

Abstract

We report metal-free organic 1,2-diketones that exhibit fast and highly efficient room-temperature phosphorescence (RTP) with high colour purity under various conditions, including solutions. RTP quantum yields reached 38.2% in solution under Ar, 54% in a polymer matrix in air, and 50% in crystalline solids in air. Moreover, the narrowband RTP consistently dominated the steady-state emission, regardless of the molecular environment. Detailed mechanistic studies using ultrafast spectroscopy, single-crystal X-ray structure analysis, and theoretical calculations revealed picosecond intersystem crossing (ISC) followed by RTP from a planar conformation. Notably, the phosphorescence rate constant kp was unambiguously established as ∼5000 s−1, which is comparable to that of platinum porphyrins (representative heavy-metal phosphor). This inherently large kp enabled the high-efficiency RTP across diverse molecular environments, thus complementing the streamlined persistent RTP approach. The mechanism behind the photofunction has been elucidated as follows: (1) the large kp is due to efficient intensity borrowing of the T1 state from the bright S3 state, (2) the rapid ISC occurs from the S1 to the T3 state because these states are nearly isoenergetic and have a considerable spin–orbit coupling, and (3) the narrowband emission results from the minimal geometry change between the T1 and S0 states. Such mechanistic understanding based on molecular orbitals, as well as the structure-RTP property relationship study, highlighted design principles embodied by the diketone planar conformer. The fast RTP strategy enables development of organic phosphors with emissions independent of environmental conditions, thereby offering alternatives to precious-metal based phosphors.

Graphical abstract: Fast, efficient, narrowband room-temperature phosphorescence from metal-free 1,2-diketones: rational design and the mechanism

Supplementary files

Article information

Article type
Edge Article
Submitted
29 Apr 2024
Accepted
01 Jun 2024
First published
03 Jun 2024
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2024,15, 10784-10793

Fast, efficient, narrowband room-temperature phosphorescence from metal-free 1,2-diketones: rational design and the mechanism

Y. Tani, K. Miyata, E. Ou, Y. Oshima, M. Komura, M. Terasaki, S. Kimura, T. Ehara, K. Kubo, K. Onda and T. Ogawa, Chem. Sci., 2024, 15, 10784 DOI: 10.1039/D4SC02841D

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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