jp8b07610_si_001.pdf (4.97 MB)
Thermally Activated Delayed Fluorescence Mediated through the Upper Triplet State Manifold in Non-Charge-Transfer Star-Shaped Triphenylamine–Carbazole Molecules
journal contribution
posted on 2018-09-28, 00:00 authored by Piotr Pander, Radoslaw Motyka, Pawel Zassowski, Marc K. Etherington, Daniele Varsano, Tales J. da Silva, Marilia J. Caldas, Przemyslaw Data, Andrew P. MonkmanThermally
activated delayed fluorescence has been found in a group
of tricarbazolylamines that are purely electron-donating, non-charge-transfer
(CT) molecules. We show that the reverse intersystem crossing step
in these materials is mediated through upper triplet states. Reverse
internal conversion is shown to be the thermally activated mechanism
behind the triplet harvesting mechanism. The strongly mixed n−π*/π–π*
character of the lowest energy optical transitions retains high oscillator
strength and gives rise to high ΦPL. Organic light-emitting
diode devices using these materials were fabricated to show very narrow
(full width at half-maximum = 38–41 nm) electroluminescence
spectra, clearly demonstrating the excitonic nature of the excited
states. This new combination of physicochemical properties of a non-CT
molecule yields thermally activated delayed fluorescence, but via
a different, physical mechanism, reverse internal conversion delayed
fluorescence.