Rational Color Tuning and Luminescent Properties of Functionalized Boron‐Containing 2‐Pyridyl Pyrrolide Complexes

Three systematically functionalized pyrrolide ligands were prepared via the coupling of methyl vinyl ketone and the respective carbaldehyde reagents, followed by treatment of the pre-formed dicarbonyl compounds with (NH4)2CO3 in order to generate the required pyrrole fragment. These ligands readily reacted with the boron reagent BPh3 to afford the complexes [(pyro)BPh2] (2a), [(noro)BPh2] (2b), and [(xaro)BPh2] (2c), where (pyro)H, (noro)H, and (xaro)H represents the 2-pyridyl, 2-quinolinyl, and 2-quinoxalinyl pyrrole groups, respectively. Complexes 2a–2c give stable solutions in air, and show strong photoluminescence with emission peak maxima located at 490 nm, 510 nm, and 575 nm, respectively. Calculations based upon time-dependent density function theory (TDDFT) show that the S1 state in these complexes is attributed to an allowed (π-symmetry) → π* (π-symmetry) transition located at the chelating pyrrolide moieties. Electroluminescence (EL) devices based on 2c were fabricated. The EL emission from 2c as the host-emitter, with the emission peak maximum shifted to 580 nm, was observed when BCP was used as the hole blocking material. This device produces saturated red-orange light-emission at an onset voltage of 8 V and a maximum brightness of 5000 cd m–2 at a driving voltage of 15 V; the external quantum yield is estimated to be 0.5 %.