Two new Cu(I) dimers chelated with
thiophene ring-introduced diphosphine
ligands [Cu(μ2-I)dppt1]2 and [Cu(μ2-I)dppt2]2 (dppt1 = 3,4-bis(diphenylphosphino)thiophene,
dppt2 = 2,3-bis(diphenylphosphino)thiophene) have been prepared and
studied in terms of photoluminescence and electroluminescence properties.
Both dimers exhibited two independent radiative decay pathways, which
are equilibrated thermally at room temperature: one is thermally activated
delay fluorescence (TADF) via the first singlet excited state (S1) decay and the other is phosphorescence via the first triplet
excited state (T1) decay. The dual emission mechanism for
both singlet and triplet harvesting, as well as excellent photoluminescence
properties such as bluish-green emission color (487 and 483 nm), short
decay times (9.46 and 7.62 μs), and high photoluminescence quantum
yields (69% and 86%) of the two Cu(I) dimers, implies their potential
to be highly efficient emitter molecules for organic light emitting
diode (OLED) applications. As a result, the optimized OLEDs with [Cu(μ2-I)dppt2]2 showed the highest efficiency, exhibiting
a current efficiency up to 32.2 cd A–1, a peak brightness
of 3.67 × 103 cd m–2, as well as
a maximum external quantum efficiency of 14.5%.