“Aggregation induced phosphorescence” active “rollover” iridium(iii) complex as a multi-stimuli-responsive luminescence material

Abstract

On reaction of 2,2′-bipyridine with iridium(III), an “aggregation induced phosphorescence (AIP)” active “rollover” complex, [Ir(PPh₃)₂(bipy-H)(Cl)(H)] (bipy-H = κ²-N,C-2,2′-bipyridine) or [Ir(bipy-H)], is obtained. The emission colour changes from bluish-green to yellowish-orange and vice versa after repeated protonation and deprotonation of [Ir(bipy-H)], respectively, which unequivocally supports its reversible nature. [Ir(bipy-H)] is sensitive to acids with different pK_a values. Tuning of the emission properties can be achieved in the presence of acids with different pK_as. This behaviour allows the complex, [Ir(bipy-H)], to function as a phosphorescent acid sensor in both solution and the solid state, as well as a chemosensor for detecting acidic and basic organic vapours. The protonated form, [Ir(bipy-H)H⁺], which is generated after protonation of [Ir(bipy-H)] can be used as a solvatochromic probe for oxygen containing solvents, and also shows vapochromic properties. The emission, absorption and ¹H NMR spectra of [Ir(bipy-H)] under acidic and basic conditions demonstrate its reversible nature. DFT based calculations suggest that changes in the electron affinity of the pyridinyl rings are responsible for all these processes.