Nanotechnologies / Materials
Energy-saving devices, Security, Bio-imaging

Development of room temperature phosphorescencematerials with naturally abundant element
Department of Applied Chemistry, Graduate School of Engineering
Associate Professor Youhei Takeda
https://researchmap.jp/read0156438?lang=en

Nanotechnologies / Materials

Abstract
Organic molecules that exhibit phosphorescence at room-temperature have attracted attention as emissive materials for highly
efficient OLED devices and bio-imaging materials with high spatiotemporal resolution, due to their long-lived emission from the excited triplet state. However, existing design strategies for room-temperature phosphorescent materials require the introduction ofrare metals and/or heavy elements such as platinum, iridium, andhalogens. In this research, we have succeeded in constructing
organic molecules that exhibit highly efficient room-temperaturephosphorescence with only light and naturally abundant elements,
such as carbon, hydrogen, and silicon. We have also demonstrated that the developed molecules actually function as emissive
materials for OLEDs and revealed that the external quantum efficiency of the OLEDs reaches one of the world-top-class values for
the OLEDs using room-temperature phosphorescent materials that
do not contain heavy elements. Furthermore, through systematic
structure-property correlation studies, the influence of molecular
structure on photophysical processes has been clarified.

▍ Background & Results
Organic molecules that exhibit phosphorescence at room temperature are attracting attention as emissive materials for highly
efficient OLED devices and bio-imaging materials with high spatiotemporal resolution, due to their long-lived luminescence fromthe excited triplet state. However, existing design strategies forroom-temperature phosphorescent materials require the introduction of rare metals and heavy elements such as platinum, iridium,and halogens. In this research, we have succeeded in constructing
organic molecules that exhibit highly efficient room-temperaturephosphorescence with only naturally abundant and light elements,
such as carbon, hydrogen, nitrogen, and silicon. First, we have focused on the electropositive characteristics of the silicon element,
one of the most common elements in nature. The introduction ofthe silicon element into the electron donor moiety of an organic
molecule composed of an electron donor and an electron acceptor
made it possible to engineer the energy level of the excited state,
which was the key to the success of this research. Detailed spectroscopic measurements revealed that the room-temperature phosphorescence is derived through a mechanism of interconversion
between energetically proximal neighboring excited states. In addition, we have fabricated OLEDs using the developed moleculesand demonstrated that they served as emissive materials in theEL devices. Furthermore, we have demonstrated that the quantum
efficiency of the OLED device using room-temperature phosphorescent materials without heavy elements is one of the highest
values so far. Furthermore, through systematic structure-property
correlation studies, we have elucidated the influence of molecular
structure on photophysical processes.

sion between energetically proximal neighboring excited statesoccurs via thermal processes. This result allows us to designroom-temperature phosphorescent molecules that do not rely on
the introduction of rare metals or heavy elements. In the future,energy-saving optical and electronic devices with high environmental compatibility and sustainability will be realized. In addition,
the long-lived luminescence lifetime of phosphorescence can beutilized to develop biologically harmonized imaging materials withhigh spatiotemporal resolution.

Figure1.a) Conventional RTP materials and b) herein developed RTP material

Figure2. The structure of developed room-temperature phosphorescence material (SiAz) and illustrative summary of this work

▍ Significance of the research and Future perspective
In this study, we have found that room-temperature phosphorescence is manifested by a mechanism through which interconverP a t e n t Japanese Patent Application No.2020-541184
De Silva, Piotr; Takeda, Youhei; Data, Przemyslaw et al. Heavy-atom-free room-temperature phosphorescent organic light-emitting diodes enabled byexcited states engineering. ACS Appl. Mater. Interfaces, 2021, 13 (2), 2899-2907. doi: 10.1021/acsami.0c17295
T r e a t i s e De Silva, Piotr; Data, Przamylsaw; Takeda, Youhei et al. The regioisomeric effect on the excited-state fate leading to room-temperature phosphorescenceor thermally activated delayed fluorescence in a dibenzophenazine-cored donor–acceptor–donor system. J. Mater. Chem. C, 2022, 10 (12), 4905-4913.
doi: 10.1039/D1TC05730H
UR
L http://www.chem.eng.osaka-u.ac.jp/~minakata-lab/ytakeda/
K e y w o r d phosphorescence, electroluminescence, emissive material, light energy, elemental strategy