Abstract
Thermally activated delayed fluorescence (TADF) is a highly temperature-dependent process and can be used in optical thermometry. TADF-based optical thermometers reported so far show fairly high-temperature sensitivity but have poor brightness and significant oxygen cross-talk. A new class of TADF emitters, Zn(II) Schiff base complexes, possess excellent brightness and high temperature sensitivity of the decay time at ambient temperature (4.1%/K change of TADF lifetime at 25 °C), enabling a resolution better than 0.03 °C. Oxygen cross-sensitivity is eliminated by covering the sensing layer (luminophore in polystyrene) with an off-stoichiometry thiol–ene polymer as an oxygen-consuming layer, and a poly(vinylidene chloride-co-acrylonitrile) layer as an oxygen barrier. The material is stable after more than 2 months of storage at ambient air, which enables long-term temperature monitoring.
Highlights
Temperature is a fundamental parameter that is measured by a variety of methods
This dependency is manifested in Thermally activated delayed fluorescence (TADF) intensity that is enhanced with the temperature and the TADF decay time that is decreased with temperature
We presented highly sensitive materials for optical temperature monitoring based on the TADF-emitting Zn(II) Schiff base complexes
Summary
Temperature is a fundamental parameter that is measured by a variety of methods. conventional temperature probes such as resistance temperature sensors are widely used offering good resolution over a broad temperature range, luminescent temperature probes represent an interesting alternative for some applications. The temperature coefficients are typically below 1%/K, in the case of the decay time read-out.[29−31,56,57] Quantum dots generally possess high quantum yields, good photostability, and strongly temperature-dependent luminescence properties[10,58] but toxicity has been a concern Fluorescent organic dyes such as rhodamine and derivatives display high brightness and no oxygen cross-talk but moderate temperature sensitivity. Fluorescence brightness, a crucial parameter for sensing and imaging applications, is moderate to poor because of low molar absorption coefficients In this contribution, we will show that a new class of TADF emitters, Zn(II) complexes with Schiff bases, combine high fluorescence brightness with highly temperature-dependent luminescence decay time and are, excellent indicators for luminescence thermometry. Could be useful for the design of reference materials for optical sensors based on phosphorescent dyes
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