Dual-Emissive Platinum(II) Metallacycles with Thiophene-Containing Bisacetylide Ligands

Three cis-diphosphino Pt­(II) metallacycles with thiophene-containing
bisacetylide ligands were synthesized and their absorption and emission
properties examined. These properties are explained by DFT and TD-DFT
analysis of ground-state as well as singlet- and triplet-state energies
and geometries. Two of the metallacycles show room-temperature dual
emission (fluorescence and phosphorescence) with different intensity
ratios. Replacing the phenylene or ethynylene groups with thiophene
rings in the bisacetylide ligand of the metallacycles results in modulation
of the S1 and T1 states to show stronger fluorescence
and weaker phosphorescence. More rigid and planar metallacycles suffer
less from energy loss due to smaller degrees of structural reorganization
and thermal deactivation. These are important factors to consider
when designing single-component dual-emissive materials for applications
such as white-emitting OLEDs, self-referencing oxygen sensors, and
hypoxia contrast agents.