A quantum dynamics study of the hyperfluorescence mechanism

Abstract

Triplet state harvesting using thermally-activated delayed fluorescence (TADF) combined with efficient Förster resonant energy transfer (FRET) is studied using quantum dynamics to understand the key properties controlling the hyperfluorescence mechanism in 4th generation organic light-emitting diodes (OLEDs).

The quest to simulate excited-state dynamics of transition metal complexes

“…Compared to MC/MR, SR methods feature a considerably lower scaling in the computational cost with regard to the system size, 26 making them more amenable to transition metal complexes. Applications revolve around (closed-shell) low-spin d 6 complexes 32,38,107-126 and d 10 systems [127][128][129][130][131] with one single exception. 132 As a further advantage, SR methods can be considered more "black-box" than MC/MR methods as they typically depend on fewer (and less critical) parameters, which makes them more user friendly.…”

“…139,140. This preference is also mirrored in excited state dynamics studies, that mostly rely on hybrid functionals 32,38,[107][108][109][110][111][112][113][114][115][116][117][118][119][120]126,[128][129][130][131] with some exceptions. [121][122][123][124]129 In addition to the general functional dependence, TDDFT is well known to suffer from its inability to describe CT excitations with standard XC functionals.…”

“…Despite these limitations, LVC has become the standard approach to calculate PES in wave-packet dynamics simulations using MCTDH for transition metal complexes 38,91,[106][107][108][109][110][112][113][114][115][116][126][127][128]130 making it possible to include up to 16 nuclear degrees of freedom. 126 One example of MCTDH using 15 degrees of freedom in a heme-CO complex is shown in Figure 5.…”

Energy transfer processes in hyperfluorescent organic light-emitting diodes

“…The fluorescent emitters are selected on the basis of high radiative decay rates, high photoluminescence quantum yields (PLQYs), and narrow emission spectra. [7][8][9][10][11][12] Hyperfluorescent OLEDs, considered as fourthgeneration OLED devices, have indeed been shown to achieve high color purity, strong light intensities, and long device lifetimes. [13][14][15][16][17] The active layers of a hyperfluorescent OLED typically consist of a host material, TADF sensitizers (10-20 wt%), and a small amount of fluorescent emitters (r1 wt%).…”

Triplet-to-Singlet Exciton Transfer in Hyperfluorescent OLED materials

“…When the pairing is successful, it is possible to take advantage of both the triplet harvesting mechanism of TADF molecules and the better luminescence properties of emitters, resulting in more efficient devices. In this sense, some design rules for the TADF dopants used in hyperfluorescence have been proposed 14,15 , and some theoretical works have aimed at providing insight on the mechanism and how it could be optimized [16][17][18] .…”