7 research outputs found
Effect of Spacer Length and Solvent on the Concentration-Driven Aggregation of Cationic Hydrogen-Bonding Donor Polythiophenes
Aggregation
of cationic isothiouronium polythiophenes with alkoxy-spacers
of different lengths at the 3-position of the thiophene ring was studied
in solvents of different polarities. Hydrogen-bonding capacity was
assessed by steady-state absorption and fluorescence spectroscopy,
whereas the aggregation in aqueous solutions was studied by electron
paramagnetic resonance spectroscopy, using paramagnetic probes of
different polarities. The two polymers displayed similar features
in respect to conformation, effect of cosolvents on aggregation, unstructured
absorption–fluorescence spectra, Stokes shifts when aggregated,
solvatochromic effect, and self-quenching concentration. However,
these polymers also showed different specific interactions with water,
Stokes shifts in water, effect of the solvent on the extent of dominant
state of the S1 level, and also different inner cavities and hydrophobic–hydrophilic
surface area in aqueous solution aggregates. Water maximized the difference
between the polymers concerning the effect of specific increases in
concentration, whereas the presence of 1,4-dioxane generated almost
identical effects on both polymers
Exciton efficiency beyond the spin statistical limit in organic light emitting diodes based on anthracene derivatives
We report two donor–acceptor (D–A) materials based on a cyanoanthracene acceptor paired with diphenylamine (DPAAnCN) and carbazole (CzAnCN) donor moieties. These compounds show hybrid locally excited (LE) charge-transfer (CT) excited states (HLCT), which we demonstrated through a combined photophysical and computational study. Vacuum-deposited organic light emitting diodes (OLEDs) using these HLCT emitters exhibit maximum external quantum efficiencies (EQEmax) close to 6%, with impressive exciton utilization efficiency (Φs) of >50%, far exceeding the spin statistic limit of 25%. We rule out triplet–triplet annihilation and thermally activated delayed fluorescence as triplet harvesting mechanisms along with horizontal orientation of emitters to enhance light outcoupling and, instead, propose a “hot exciton” channel involving the nearly isoenergetic T2 and S1 states.</p