Aggregation‐Induced Emission Activity in Iridium(III) Diimine Complexes: Investigations of Their Vapochromic Properties

Abstract

Two iridium(III) diimine complexes [mono(1,10-phenanthroline) bis(triphenylphosphine)(dihydrido)iridium(III) hexafluorophosphate (1) and mono(1,10-phenanthroline)bis(triphenylphosphine)(hydrido)(chloro)iridium(III) hexafluorophosphate (2)] have been synthesized from a single two-step reaction. The structures of 1 and 2 both adopt distorted octahedral geometries, as established by single-crystal X-ray diffraction. The complexes, upon irradiation with UV light at 365 nm, emit faint light in solution and bright light in the solid state. The ground- and excited-state properties of these complexes were investigated through density functional theory (DFT) and time-dependent DFT calculations. The calculated energies for the transitions from the ground state to the singlet and triplet excited states were close to those determined from the experimental absorption and emission. Their molecular orbitals were also exploited to compute the ground-state dipole moments and redox potentials. Several experiments were performed to demonstrate the "aggregation-induced emission" (AIE) activity of these complexes. AIE was triggered by the restricted intramolecular rotation of the rotating units (phenyls in triphenyphosphines) in these molecules in the solid state. The solid thin films of 1 and 2 exhibit solvent-polarity-dependent vapour-responsive emission properties (vapoluminescent). The rationale for the different emission behavior in the solid state has been thoroughly investigated. The packing diagrams of 1 and 2 show that there is enough space available to accommodate small organic solvent molecules inside the crystal lattices.