A system pairing the luminescent core of [Ir(ppy)2L 2]+ (ppy = 2-phenylpyridine) with simple hydrazine ancillary ligands (L = N2H4) has been prepared for the direct optical detection of carbon dioxide (CO2). Silver-assisted and silver-free techniques were used for the successful introduction of N 2H4 into the [Ir(ppy)2Cl]2 coordination sphere at room temperature to give the corresponding biscyclometalated iridium(III) hydrazino species as either a CF3SO3 - (OTf-, 2a) or Cl- (2b) salt. The silver-free route was accomplished by the direct replacement of the ligated Cl- using a slight excess of hydrazine. The luminescence profile of the cationic iridium(III) hydrazino complex 2a (λmax = 501 nm) undergoes a red shift (λmax = 524 nm), accompanied by a change in the peak shape during exposure to CO2 in solution. The spectral changes observed are attributed to the formation of the corresponding neutral carbazate species Ir(ppy)2(H2NNHCOO) (3) and are not consistent with protonation of the ligated hydrazine. Conversion of the hydrazino species to the carbazate species is solvent-dependent and irreversible. The hydrazino and carbazate species have been structurally characterized by single-crystal X-ray diffraction; both compounds exhibit long-lived and intense room temperature luminescence in solution with - = 1.56 and 1.80 μs and ωem = 0.42 and 0.45, respectively.
|Original language||English (US)|
|Number of pages||9|
|State||Published - Dec 19 2011|