Abstracts

In the past decade, luminescence thermometry has made significant advancements, approaching current measurement technologies. Typically, a thermometer performance is evaluated based on the relative thermal sensitivity (S_r) and temperature uncertainty (dT). Some thermometric parameters (∆) of a single emitting center can be explored and combined, such as emission intensity, spectral positions of absorption and emission bands, emission bandwidth, anisotropy, luminescence decay time, and relative intensity between two emission bands (ratiometric systems). However, in the literature there are few works that explores thermometry in Ir^III complexes. In Ir^III complexes, the emission comes from the ³LC-^1,3MLCT hybrid state, with triplet ³MLCT being dominant at high temperatures. This emission experiences strong temperature dependence due to the rigidochromic effect. Therefore, we report the synthesis of an Ir^III-complex and thermometry studies based on the performance of a multiparametric luminescent thermometer. To make this possible, the synthesis consisted of the preparation of a μ-chlorobridged cyclometalated Ir^III dimer [Ir(Fppy)₂(μ-Cl)₂Ir(Fppy)₂], followed by the insertion of the ancillary ligand pdc to form the heteroleptic complex [Ir(Fppy)₂pdc], where Fppy = 2-(2,4-difluorophenyl) and pdc = 2,4-pyridinedicarboxylic acid, resulting in a yellow solution with a strong green emission under UV irradiation. After slow evaporation of solvents, the crude product was purified by column chromatography with silica gel. The complex [Ir(Fppy)₂pdc] was obtained as a yellow powder. Yield: 87%. Quantum yield (Φ_{DMSO solution}): 47%. The emission spectrum of the complex [Ir(Fppy)₂pdc] (l_max = 553 nm) at RT, exhibited a broadened band with an unstructured profile, indicating a greater ³MLCT character. Emission spectra were acquired varying the temperature from 11 to 320 K, revealing spectral changes as the temperature decreased. At lower temperatures, bands appeared at 485 nm and 513 nm, attributed to the emission of ³LC vibronic splittings, which exhibit practically invariable energies with increasing rigidity. However, it is notable that the ³MLCT band is strongly influenced by temperature, with the rigidochromic effect destabilizing it, resulting in a shift to lower energies as the temperature increases. The thermally coupled nature of the ³LC/³MLCT levels enabled us to utilize the ratiometric approach, resulting in a maximum S_r of 1.25% K^-1 within the 11 – 125 K temperature range. By using the ³MLCT band shift parameter (18507 – 17410 cm^-1), it was possible to obtain a maximum S_r of 0.033% K^-1 in all temperature range. Finally, using the lifetime ∆, a high sensitivity of 4.40% K^-1 (11 – 125 K) was found. Thus, these results place the multiparametric approach using the luminescence of Ir^III complexes at the center of attention in luminescence thermometry, demonstrating new paths for thermometry.