Luminescent Dinuclear Cu(I) Complexes Containing Rigid Tetraphosphine Ligands

The
synthesis and the photophysics of three dinuclear copper­(I)
complexes containing bis­(bidentate)­phosphine ligands are described.
The steric constraint imposed by tetrakis­(di­(2-methoxyphenyl)­phosphanyl)­cyclobutane)
(o-MeO-dppcb) in combination with 2,9-dimethyl-1,10-phenanthroline
in one of the complexes leads to interesting photophysical properties.
The compound shows an intense emission at room temperature in deoxygenated
acetonitrile solution (Φ = 49%) and a long excited-state lifetime
(13.8 μs). Interestingly, at low temperature, 77 K, the emission
maximum shifts to lower energy, and the excited-state lifetime increases.
This observation leads to the conclusion that a mixing between the
excited triplet and singlet states is possible and that the degree
of mixing and population of state strongly depends on temperature,
as the energy difference is quite small. The electroluminescent properties
of this compound were therefore tested in light-emitting electrochemical
cells (LEECs), proving that the bright emission can also be obtained
by electrically driven population of the singlet state.