Not just that, the introduced substances showcased effective thermally activated delayed fluorescence (TADF) and enabled high performance organic light-emitting diodes (OLEDs) devices.
“Most MCL substances generate two colours by switching between a stable state and one metastable state. To realize multi-colour MCL, more metastable states are essential,” explain Lecturers Santoshi Minakata and Youhei Takeda at the Department of Applied Chemistry, Graduate School of Engineering of Osaka University. To prepare these states, the chemist group headed by Minakata and Takeda crafted a novel molecule by applying a conformational switchable phenothiazine as the donor.
“By making the use of a lucrative and unique acceptor, dibenzophenazine, which we previously developed, we made a PTZ-DBPHZ-PTZ triad,” says Takeda. “In this structure, the PTZ moiety could take two distinct conformers, which therefore in principle creates in total four metastable states as a whole molecule.”
In response to heating, grinding and fuming, the molecule switched its colour between red, orange and yellow. The group found that the three colours derive from distinct conformers in which each PTZ takes either an equatorial or axial conformation relative to the DBPHZ core. “For red, both of PTZ units take an equatorial – axial conformer, and for yellow, PTZ had an axial-axial conformer.”
Most OLEDs devices with high energy conversion efficacies depend on costly precious metals. TADF light emitting devices, on the other hand, can accomplish equal or better efficacy at much lower cost, which is why they have gained popularity for the design of displays in daily electronics like smart phones.
In association with the scientist team at Durham University, the United Kingdom, headed by Dr. Data and Lecturer Monkam, they successfully made highly effective OLED devices by applying the novel developed MCL-TADF molecule as an emissive substance. Incorporating the PTZ-DBPHZ-PTZ triad into a light emitting device resulted in an efficacy three times higher than the theoretical maximum of conventional fluorescent substances
Takeda days that, “Our molecule could become a basis for effective light-emitting devices and pressure and temperature responsive sensors in the future.”
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