Tunable Nd3+ dimer luminescent molecular thermometer via Stark sublevels

Abstract

The near-infrared (NIR) luminescence thermometry performance of the Nd-based dimer {[Nd(acac)3]2(μ- bpm)} (Nd2) (where acac− denotes acetylacetonate and bpm is 2,2’-bipyrimidine) was investigated under both ligand- and metal-centered excitation. To resolve the Stark components of the 4F3/2 → 4 I11/2 tran-sition, ab initio electronic structure calculations were performed. The opposite temperature dependences of the lower- and higher-energy components of the 4F3/2 level were used as a thermometric parameter, expressed through the luminescence intensity ratio (LIR). Under ligand-centered excitation at 370 nm, Nd2 exhibited a maximum relative sensitivity (Sm) of 2.1% K−1 at 85 K, across the 85–285 K range, demon- strating excellent thermal performance at low temperatures. Considering the relevance of NIR-to-NIR emitters for biomedical applications, the thermometric response was also evaluated under metal-cen- tered excitation at 804 nm within the physiological range (294–332 K). In this case, an unprecedented Sm value of 2.5% K−1 at 294 K was obtained, setting a new benchmark for Nd-based molecular thermometers and highlighting its potential for biological temperature sensing. Overall, Nd2 operates as a versatile lumi- nescent molecular thermometer whose thermal response can be tuned simply by selecting the excitation wavelength (UV or NIR), enabling adaptable, application-specific thermometric behavior.