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Uncovering Single-Molecule Photophysical Heterogeneity of Bright, Thermally Activated Delayed Fluorescence Emitters Dispersed in Glassy Hosts
journal contribution
posted on 2016-10-04, 19:55 authored by Rodrigo Noriega, Edward S. Barnard, Benedikt Ursprung, Benjamin
L. Cotts, Samuel B. Penwell, P. James Schuck, Naomi S. GinsbergRecently developed
all-organic emitters used in display applications
achieve high brightness by harvesting triplet populations via thermally
activated delayed fluorescence. The photophysical properties of these
emitters therefore involve new inherent complexities and are strongly
affected by interactions with their host material in the solid state.
Ensemble measurements occlude the molecular details of how host–guest
interactions determine fundamental properties such as the essential
balance of singlet oscillator strength and triplet harvesting. Therefore,
using time-resolved fluorescence spectroscopy, we interrogate these
emitters at the single-molecule level and compare their properties
in two distinct glassy polymer hosts. We find that nonbonding interactions
with aromatic moieties in the host appear to mediate the molecular
configurations of the emitters, but also promote nonradiative quenching
pathways. We also find substantial heterogeneity in the time-resolved
photoluminescence of these emitters, which is dominated by static
disorder in the polymer. Finally, since singlet–triplet cycling
underpins the mechanism for increased brightness, we present the first
room-temperature measurement of singlet–triplet equilibration
dynamics in this family of emitters. Our observations present a molecular-scale
interrogation of host–guest interactions in a disordered film,
with implications for highly efficient organic light-emitting devices.
Combining a single-molecule experimental technique with an emitter
that is sensitive to triplet dynamics, yet read out via fluorescence,
should also provide a complementary approach to performing fundamental
studies of glassy materials over a large dynamic range of time scales.
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triplet harvestingnonradiative quenching pathwayssingle-molecule leveltime-resolved photoluminescenceUncovering Single-Molecule Photophysical HeterogeneityFluorescence Emitters Disperseddisplay applicationsnonbonding interactionsall-organic emittersThermally Activatedharvesting triplet populationsGlassy Hoststime scalestime-resolved fluorescence spectroscopypolymer hostsphotophysical propertiestriplet dynamicshost materialensemble measurements occludemolecular-scale interrogationroom-temperature measurementsinglet oscillator strengthlight-emitting devices
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