Photoswitches with different numbers of azo chromophores for molecular solar thermal storage.
basic_science · Level V
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- Record sourced from PubMed, PMID 36373235.
- Also identified by DOI 10.1039/d2sm01073a.
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Abstract
We investigate three azo-chromophore-containing photoswitches (1, 2 and 3) for molecular solar thermal storage (MOST) based on reversible <i>Z</i>-<i>E</i> isomerization. 1, 2 and 3 are photoswitchable compounds that contain one, two and three azo chromophores, respectively. In solution, 1, 2 and 3 were charged <i>via</i> UV-light-induced <i>E</i>-to-<i>Z</i> isomerization. Among these three compounds, 2 exhibited an energy density as high as 272 ± 1.8 J g<sup>-1</sup>, which showed the best energy storage performance. This result originated from the low molecular weight, a high degree of photoisomerization, and moderate steric hindrance of 2, which demonstrated the advantages of the <i>meta</i>-bisazobenzene structure for MOST. In addition, we studied the performances of these photoswitches in the solvent-free state. Only 1 showed photoinduced reversible solid-to-liquid transitions, which enabled the charging of 1 in a solvent-free state. The stored energy density for 1 in a solvent-free state was 237 ± 1.5 J g<sup>-1</sup>. By contrast, 2 and 3 could not be charged in the solvent-free state due to the lack of solid-state photoisomerization. Our findings provide a better understanding of the structure-performance relationship for azobenzenebased MOST and pave the way for the development of high-density solar thermal fuels.