Persistent Radical Tetrathiafulvalene‐Based 2D Metal‐Organic Frameworks and Their Application in Efficient Photothermal Conversion

Abstract

A series of stable radical 2D metal‐organic frameworks has been assembled. (m‐TTFTB)3 (m‐Tetrathiafulvalene‐tetrabenzoate) trimer building blocks are beneficial for the stability of the radicals due to delocalization of the unpaired electron. Hexanuclear rare‐earth‐cluster‐based 1D chains further enhance the stability of the frameworks. The radical state of the middle TTF in the trimer has been observed by the change of central C−C and C−S bond distances and the configuration of the TTF by single‐crystal X‐ray diffraction. The radical characteristics are also confirmed by electron paramagnetic resonance, UV/Vis–NIR absorption, and X‐ray photoelectron spectroscopy experiments. Stability tests showed that the radicals are stable even in solutions and under acid/base environments (pH 1–12). Owing to efficient light absorption due to intramolecular charge transfer, low thermal conductivity, and outstanding stability, the radical 2D Dy‐MOF shows excellent photothermal properties, an increase of 34.7 °C within 240 s under one‐sun illumination.

Stable open-shell aromatic nitric acid radicals: accessing highly efficient photothermal conversion with restricted radiative decay

“…After demethylation, the PLQYs of these radical products are significantly reduced and all of them showed low fluorescence quantum yields lower than 1% (TableS1), which indicate the formation of radicals. These results are in good agreement with the previous work in diradicaloids and multiple radicaloids which usually showed obviously lowered PLQY 56. In order to study the chemical and electrochemical stability, the cyclic voltammetry (CV) test was conducted in film and solution.…”

“…In the solid-state, these radical materials showed high spin concentration, and this will lead to highly nonradiative decay and enhanced photothermal conversion efficiency (Figure 4D). 56,58 The PLQY with the value of demethylated counterparts TPA-TPA-O6, TPA-TPZ-O6, TPA-PY-O8, and Spiro-O8 are recorded as 0.1%, 0.9%, 1.0%, and 0.3% and the PL wavelength is around the corresponding trace protonated phenoxy precursors, respectively. Due to the high concentration of radical spin, the nonradiative decay will be largely boosted, which efficiently enhances the photothermal conversion of TPA-TPA-O6 in the solid state.…”

“…These results are in good agreement with the previous work in diradicaloids and multiple radicaloids which usually showed obviously lowered PLQY. 56 In order to study the chemical and electrochemical stability, the cyclic voltammetry (CV) test was conducted in film and solution. It can be observed from Figure 3 that all the demethylated counterparts exhibited highly reversible CV curves under the oxidation process and showed negligible change after scanning for 15 cycles (Figure 2).…”

“…10,12,30,31,59 According to the powder absorption spectra, ESR and PL measurements, we propose that the TPA-TPA-O6 might show promising photothermal conversion performance due to the radical-promoted nonradiative decay (Figure 4 and Table S1). 48,56 The photothermal property of star-shaped radical materials was evaluated by monitoring the temperature increment under irradiation via IR thermal camera, and the detailed test condition is provided in the SI. As shown in Figure 6A, star-shaped radical materials were irradiated by an 808 nm laser with energy power of 0.8 W cm −2 .…”

“…Comparing with other types of organic photothermal materials, TPA-TPA-O6 exhibit extremely wide absorption spectra 10,12,30,31,59. According to the powder absorption spectra, ESR and PL measurements, we propose that the TPA-TPA-O6 might show promising photothermal conversion performance due to the radical-promoted nonradiative decay (Figure4and TableS1) 48,56. The photothermal property of star-shaped radical materials was evaluated by monitoring the temperature increment under irradiation via IR thermal…”