Bright Sky-Blue Phosphorescence of [n-Bu4N][Pt(4,6-dFPPY)(CN)2]: Synthesis, Crystal Structure, and Detailed Photophysical Studies

This work describes the synthesis, crystal structure, and detailed photophysical studies of [n-Bu4N][Pt(4,6-dFppy)-(CN)(2)] (n-Bu = n-butyl, 4,6-dFppy = (4',6'-difluorophenyl)pyridinate). The material can easily be prepared in high yield and purity by the reaction of [Pt(4,6-dFppy)(H-4,6-dFppy)Cl], [n-Bu4N]Cl, and KCN in CH2Cl2. Because of the bulky counterion [n-Bu4N](+), Pt-Pt interactions, which frequently lead to aggregate formation, are suppressed in the solid state. Thus, monomer emission is observed. The phosphorescence quantum yield of the neat powder amounts to phi(PL) = 60% at ambient temperature and decays with 19 mu s. In tetrahydrofuran (THF) solution, on the other hand, the emission decay time is with 0.26 mu s distinctly shorter, and the quantum yield is very low. By means of emission decay time studies in frozen THF and investigations of the highly resolved single crystal emission at 1.2 K, we can assign the emitting T-1 state of the compound as being largely of ligand centered ((LC)-L-3, (3)pi pi*) character. The observed differences of the emission properties of the neat powder compared to the fluid solution are rationalized with an energy stabilization of quenching dd* states in solution because of molecular distortions and/or bond elongations.