Abstract
In this work, novel temperature-sensitive indicators and materials for use in optical temperature sensors are presented. The focus lies in the synthesis and characterization of thermally activated delayed fluorescent (TADF) indicators and their integration into novel temperature sensor materials. In contrast to most other luminescent temperature indicators, TADF-based indicators show particularly strong temperature dependency of their lifetimes, which are easy and precise to measure. However, with few exceptions, the TADF-based indicators known to date have very long lifetimes in the range of several milliseconds resulting in cross-sensitivity to oxygen. Thus, the range of applications is limited because special oxygen-blocking matrices are required.
The main goal of this doctoral thesis is to develop new TADF-based indicators with lifetimes in the microsecond range and thus with lower oxygen crosstalk. In total, three different classes of TADF-emitting organometallic indicators are investigated.
The first class is based on zinc(II) donor-acceptor Schiff base complexes, which exhibit high temperature-dependent lifetimes (~-3%/°C). Here it is shown that the use of a stronger electron acceptor reduces the lifetime by a factor of seven. Unfortunately, this is accompanied by a drastic reduction in quantum yield. Nevertheless, the Schiff base complex with the best properties was incorporated into cell-penetrating nanoparticles. The nanoparticles have a very high temperature-dependent lifetime of -5%/°C, but their relatively long lifetime of 1 ms allows only temperature measurements under anoxic conditions.
The second generation of temperature indicators is based on zirconium(IV) pyridinedipyrrolide complexes. Here, a total of nine complexes are synthesized using different pyridinedipyrrolide ligands. In contrast to the zinc(II) Schiff base complexes, all complexes emit pure TADF without prompt fluorescence and show monoexponential lifetimes in the order of tens to hundreds of microseconds. They also show only slightly lower sensitivity between -2.5 and -2.9%/°C compared to the Schiff base complexes. By embedding the complexes in oxygen-impermeable polymers, it is possible to fabricate both planar temperature sensors and nanoparticles with minimal oxygen crosstalk. The nanoparticles proved to be suitable for imaging temperature distribution in microfluidic chips and cancer cells.
A further reduction in lifetime is achieved in a series of platinum(II) pyridinedipyrrolide complexes. For these complexes, lifetimes range from 9.5 to 135 µs, and the negative influence of oxygen can be further reduced. Theoretical and photophysical studies show that both TADF and phosphorescence contribute to the total emission and the ratio between the two can be fine-tuned from nearly pure TADF emission to a TADF/phosphorescence ratio of 1/4 by modifying the ligands. The temperature indicators can be used for lifetime readout, albeit with lower sensitivity than the other two indicator classes. However, these indicators allow an alternative readout method by using the temperature-dependent ratio between the green TADF and orange phosphorescence emission bands enabling temperature measurement with an ordinary RGB camera.
The main goal of this doctoral thesis is to develop new TADF-based indicators with lifetimes in the microsecond range and thus with lower oxygen crosstalk. In total, three different classes of TADF-emitting organometallic indicators are investigated.
The first class is based on zinc(II) donor-acceptor Schiff base complexes, which exhibit high temperature-dependent lifetimes (~-3%/°C). Here it is shown that the use of a stronger electron acceptor reduces the lifetime by a factor of seven. Unfortunately, this is accompanied by a drastic reduction in quantum yield. Nevertheless, the Schiff base complex with the best properties was incorporated into cell-penetrating nanoparticles. The nanoparticles have a very high temperature-dependent lifetime of -5%/°C, but their relatively long lifetime of 1 ms allows only temperature measurements under anoxic conditions.
The second generation of temperature indicators is based on zirconium(IV) pyridinedipyrrolide complexes. Here, a total of nine complexes are synthesized using different pyridinedipyrrolide ligands. In contrast to the zinc(II) Schiff base complexes, all complexes emit pure TADF without prompt fluorescence and show monoexponential lifetimes in the order of tens to hundreds of microseconds. They also show only slightly lower sensitivity between -2.5 and -2.9%/°C compared to the Schiff base complexes. By embedding the complexes in oxygen-impermeable polymers, it is possible to fabricate both planar temperature sensors and nanoparticles with minimal oxygen crosstalk. The nanoparticles proved to be suitable for imaging temperature distribution in microfluidic chips and cancer cells.
A further reduction in lifetime is achieved in a series of platinum(II) pyridinedipyrrolide complexes. For these complexes, lifetimes range from 9.5 to 135 µs, and the negative influence of oxygen can be further reduced. Theoretical and photophysical studies show that both TADF and phosphorescence contribute to the total emission and the ratio between the two can be fine-tuned from nearly pure TADF emission to a TADF/phosphorescence ratio of 1/4 by modifying the ligands. The temperature indicators can be used for lifetime readout, albeit with lower sensitivity than the other two indicator classes. However, these indicators allow an alternative readout method by using the temperature-dependent ratio between the green TADF and orange phosphorescence emission bands enabling temperature measurement with an ordinary RGB camera.
| Translated title of the contribution | Entwurf und Charakterisierung von thermisch aktivierten verzögerten Fluoreszenzmaterialien für die optische Temperaturmessung |
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| Original language | English |
| Qualification | Doctor of Technology |
| Awarding Institution |
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| Supervisors/Advisors |
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| Publication status | Published - 24 Nov 2024 |
