Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume -, Issue -, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.202203238
Keywords
aromaticity; fused-ring systems; halochromism; protonation; sulfur heterocycles
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Funding
- National Key Research and Development Program of China
- National Natural Science Foundation of China
- Natural Science Foundation of Shanghai
- [2018YFA0209401]
- [22171053]
- [21733003]
- [21ZR1409600]
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Three S-fused PAHs with cyclopenta[b]thiopyran moieties were successfully synthesized and showed significant halochromic properties. The longest PAH exhibited absorption onset at 1110 nm and was selectively protonated by stronger acid. The non-emissive S-fused PAHs showed strong fluorescence after protonation, which violated the Kasha's rule.
Three S-fused polycyclic aromatic hydrocarbons (PAHs) bearing cyclopenta[b]thiopyran moieties have been designed and successfully synthesized. With the conjugation extension, the absorption onset of the longest PAH reaches 1110 nm. All the three S-fused PAHs exhibit significant halochromic properties in both solution and solid states. Upon protonation, the proton is incorporated on the cyclopentadiene ring while the positive charge is localized on the thiopyrylium ring. Moreover, no significant difference can be found for the two shorter PAHs upon the protonation by different organic acids, such as trifluoroacetic acid (TFA) and trifluoromethanesulfonic acid (TfOH), while the longest PAH can be only mono-protonated by TFA but di-protonated by stronger TfOH. Furthermore, after protonation, the non-emissive S-fused PAHs exhibit strong fluorescence and can be regenerated by simply neutralization with triethylamine. The enhanced emission of mono-protonated products stem from S-2 -> S-0 transitions, which disobey the Kasha's rule.
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