ic7b02002_si_002.pdf (248.69 kB)
Thermally Activated Delayed Fluorescence from Ag(I) Complexes: A Route to 100% Quantum Yield at Unprecedentedly Short Decay Time
journal contribution
posted on 2017-10-20, 19:20 authored by Marsel Z. Shafikov, Alfiya F. Suleymanova, Rafał Czerwieniec, Hartmut YersinThe
four new Ag(I) complexes Ag(phen)(P2-nCB) (1), Ag(idmp)(P2-nCB) (2), Ag(dmp)(P2-nCB) (3), and Ag(dbp)(P2-nCB) (4) with P2-nCB = bis(diphenylphosphine)-nido-carborane, phen = 1,10-phenanthroline, idmp = 4,7-dimethyl-1,10-phenanthroline,
dmp = 2,9-dimethyl-1,10-phenanthroline, and dbp = 2,9-di-n-butyl-1,10-phenanthroline were designed to demonstrate how to develop
Ag(I) complexes that exhibit highly efficient thermally activated
delayed fluorescence (TADF). The substituents on the 1,10-phenanthroline
ligand affect the photophysical properties strongly (i) electronically
via influencing the radiative rate of the S1 → S0 transition and (ii) structurally by rigidifying the molecular
geometry with respect to geometry changes occurring in the lowest
excited S1 and T1 states. The oscillator strength
of the S1 ↔ S0 transition f(S1 ↔ S0)an important parameter
for the TADF efficiency being proportional to the radiative ratecan
be increased from f(S1 ↔ S0) = 0.0258 for Ag(phen)(P2-nCB) (1) to f(S1 ↔ S0) = 0.0536
for Ag(dbp)(P2-nCB) (4), as calculated for
the T1 state optimized geometries. This parameter governs
the radiative TADF decay time (τr) at ambient temperature,
found to be τr = 5.6 μs for Ag(phen)(P2-nCB) (1) but only τr = 1.4
μs for Ag(dbp)(P2-nCB) (4)a
record TADF value. In parallel, the photoluminescence quantum yield
(ΦPL) measured for powder samples at ambient temperature
is boosted up from ΦPL = 36% for Ag(phen)(P2-nCB) (1) to ΦPL = 100% for Ag(dbp)(P2-nCB) (4). This is a consequence of a cooperative effect of both decreasing the
nonradiative decay rate and increasing the radiative decay rate in
the series from Ag(phen)(P2-nCB) (1), Ag(idmp)(P2-nCB) (2), and Ag(dmp)(P2-nCB) (3) to Ag(dbp)(P2-nCB) (4). Another
parameter important for the TADF behavior is the activation energy
of the S1 state from the state T1, ΔE(S1–T1). Experimentally it
is determined for the complexes Ag(dmp)(P2-nCB) (3) and Ag(dbp)(P2-nCB) (4) to be of
moderate size of ΔE(S1–T1) = 650 cm–1.
