A temperature sensor with a wide spectral range based on a dual-emissive TADF dendrimer system

Dual emission from thermally activated delayed fluorescence (TADF) emitters is often difficult to observe, especially in solution, limited by Kasha's rule. Two TADF dendrimers containing N-doped polycyclic aromatic hydrocarbons as acceptors are designed and synthesized. Compound 2GCzBPN, having a strongly twisted geometry, exhibits TADF, while 2GCzBPPZ, possessing a less twisted geometry, shows dual emission associated with the monomer and aggregate that is TADF. The demonstration reveals that 2GCzBPPZ can serve as a temperature sensor with excellent temperature sensitivity and remarkably wide emission color response in solution. By embedding 2GCzBPPZ in paraffin we demonstrate a spatial-temperature sensor that shows a noticeable emission shift from yellow to green and ultimately to blue as the temperature increases from 20 to 200 °C. We finally demonstrate the utility of these TADF dendrimers in solution-processed organic light-emitting diodes.

Tunable Self-Referenced Molecular Thermometers via Manipulation of Dual Emission in Platinum(II) Pyridinedipyrrolide Complexes

Optical temperature sensors based on self-referenced readout schemes such as the emission ratio and the decay time are crucial for a wide range of applications, with the former often preferred due to simplicity of instrumentation. This work describes a new group of dually emitting dyes, platinum(II) pincer complexes, that can be used directly for ratiometric temperature sensing without an additional reference material. They consist of Pt(II) metal center surrounded by a pyridinedipyrrolide ligand (PDP) and a terminal ligand (benzonitrile, pyridine, 1-butylimidazol or carbon monoxide). Upon excitation with blue light, these complexes exhibit green to orange emission, with quantum yields in anoxic toluene at 25 °C ranging from 13% to 86% and decay times spanning from 8.5 to 97 μs. The emission is attributed to simultaneous thermally activated delayed fluorescence (TADF) and phosphorescence processes on the basis of photophysical investigations and DFT calculations. Rather uniquely, simple manipulations in substituents of the PDP ligand and alteration of the terminal ligand allow fine-tuning of the ratio between TADF and phosphorescence from almost 100% TADF emission (Pt(MesPDPC6F5(BN)) to over 80% of phosphorescence (Pt(PhPDPPh(BuIm)). Apart from ratiometric capabilities, the complexes also are useful as decay time-based temperature indicators with temperature coefficients exceeding 1.5% K-1 in most cases. Immobilization of the dyes into oxygen-impermeable polyacrylonitrile produces temperature sensing materials that can be read out with an ordinary RGB camera or a smartphone. In addition, Pt(PhPDPPh)Py can be incorporated into biocompatible RL100 nanoparticles suitable for cellular nanothermometry, as we demonstrate with temperature measurements in multicellular colon cancer spheroids.

Long-Lived Room-Temperature Phosphorescence for Visual and Quantitative Detection of Oxygen

An unconventional organic molecule (TBBU) showing obvious long-lived room temperature phosphorescence (RTP) is reported. X-ray single crystal analysis demonstrates that TBBU molecules are packed in a unique fashion with side-by-side arranged intermolecular aromatic rings, which is entirely different from the RTP molecules reported to date. Theoretical calculations verify that the extraordinary intermolecular interaction between neighboring molecules plays an important role in RTP of TBBU crystals. More importantly, the polymer film doped with TBBU inherits its distinctive RTP property, which is highly sensitive to oxygen. The color of the doped film changes and its RTP lifetime drops abruptly through a dynamic collisional quenching mechanism with increasing oxygen fraction, enabling visual and quantitative detection of oxygen. Through analyzing the grayscale of the phosphorescence images, a facile method is developed for rapid, visual, and quantitative detection of oxygen in the air.

Modulation of Thermally Activated Delayed Fluorescence in Waterborne Polyurethanes via Charge-Transfer Effect

Here, we designed several waterborne polyurethanes (WPUs) with efficient thermally activated delayed fluorescence (TADF) via serving charge-transfer (CT) states as a mediate bridge between singlet and triplet states to boost reverse intersystem crossing (RISC). By tuning substituents of diphenyl sulfone (DS), we found that O,O'- and S,S'-substituted DS covalently incorporated in WPUs solely show typical fluorescence emission with lifetimes in the nanosecond range. Interestingly, TADF appears by replacing the substituent with the nitrogen atom, of which lifetimes are up to ≈10 microseconds and ≈1 millisecond in air and vacuum, respectively, even though the energy gap between singlet and triplet states (ΔE_ST ) is still large for generating TADF. To explain this phenomenon, an energy level mode based on CT states and an ³ (n-π*) receiver state was proposed. By the rational modulation of CT states, it is possible to tune the ΔE_ST to render TADF-based materials suitable for versatile applications.

Synthesis of Linseed Oil-Based Waterborne Urethane Oil Wood Coatings

The linseed oil glyceride (LOG) was synthesized by using a transesterification process with a glycerol/linseed oil molar ratio of 1.0. The waterborne urethane oil (WUO) wood coating was prepared by acetone process. First, dimethylolpropionic acid was reacted with hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI), followed by adding LOG at various NCO/OH molars of 0.7, 0.8, and 0.9, respectively, and the COOH-containing prepolymer was obtained. Then, the ionomer which was prepared by neutralizing prepolymer with trimethylamine, was dispersed by adding deionized water, and the water⁻acetone dispersion was obtained. Finally, the acetone was removed by vacuum distillation. In the whole synthesized process, the LOG and COOH-containing prepolymer could be steadily synthesized by FTIR analysis, and the weight-average molecular weight and polydispersity of COOH-containing prepolymer increased with an increase of NCO/OH molar ratios. During the water dispersion process of the ionomer acetone solution, the point of phase inversion was prolonged, meaning the solid content decreased with an increase of NCO/OH molar ratios. After acetone was removed, the color of WUO was milky-white, and it was weakly alkaline and possessed a pseudoplastic fluid behavior. The particle size of WUO increased with increasing of NCO/OH molar ratios, however, the storage stability was extended for HDI and shortened for IPDI synthesized with increasing of NCO/OH molar ratios.