Dual emission from an iridium(III) complex/counter anion ion pair

Ir(tpy)(2)](PF6)(3) (tpy = 2,2':6',2 ''-terpyridine) dissolved in CH3CN was found to exhibit dual color luminescent emission depending on the excitation wavelength. Specifically, blue and green emissions were obtained with excitation at 350 and 410 nm, respectively. Because the associated emission spectra were consistent with those of [Ir(tpy)(2)]Cl-3 in water and [Ir(tpy)(2)](PF6)(3) in the crystalline state, respectively, this dual emission is attributed to emissions from the [Ir(tpy)(2)](3+) cation and its ion pair [Ir(tpy)(2)](3+)center dot PF6-. The emission is assigned to the (3)pi-pi* transition of the ligands based on time-dependent density functional theory (TD-DFT) calculations. Conversely, [Ir(tpy)(2)]I-3 in CH3CN shows emission due to [Ir(tpy)(2)](3+) but not [Ir(tpy)(2)](3+)center dot I-, while crystalline [Ir(tpy)(2)]I-3 emits red luminescence at 77 K that is inconsistent with that from [Ir(tpy)(2)](3+). Since the emission energies of crystalline [Ir(tpy)(2)]X-3 (X- = Cl-, Br- or I-) show a good correlation with the electron affinity of X, the emissions are assigned to a counter anion to complex ion charge-transfer transition. This hypothesis is supported by TD-DFT calculations regarding [Ir(tpy)(2)](3+)center dot X-.

Automated summary

The complex [Ir(tpy)(2)](PF6)(3) exhibited dual color luminescent emission in CH3CN, with blue and green emissions attributed to cation and ion pair emissions, supported by TD-DFT calculations. On the other hand, [Ir(tpy)(2)]I-3 in CH3CN showed emissions solely from the cation, while crystalline [Ir(tpy)(2)]I-3 exhibited red luminescence inconsistent with cation emissions, with TD-DFT calculations supporting a charge-transfer transition hypothesis.