Tellurium-fused aromatic hydrocarbons have attracted numerous attention due to their unique properties as well as the synthetic challenges. However, the synthesis towards organotellurium molecules falls much behind those for other...

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 S2→S0 transitions, which disobey the Kasha's rule.

Chemoselective 6-endo-dig and ring-expansion cycloisomerizations have been discovered for ortho-disubstituted thiophene derivatives bearing 1-en-3-yne moieties.

Incorporation of tellurium into polycyclic compounds may endow them with unique chemical and optoelectronic properties which are not observed in their lighter chalcogen analogues. Herein, a telluropyran‐containing polycyclic compound (T1) synthesized through a ring‐expansion reaction from the corresponding tellurophene analogue can be reversibly oxidized into halogen adducts T1•X2 (X=Cl, Br, I) with the formation of two Te−X bonds. Their chemical structures have been verified by two‐dimensional 1H‐1H correlation spectroscopy and single crystal X‐ray diffraction analysis. The halogen oxidations of T1 and the reverse thermal eliminations as well as the halogen exchange in halogen adducts T1•X2 have been systematically investigated and compared by UV‐vis absorption titration, electrochemical measurements, thermogravimetric analysis, and density functional calculations (DFT). The oxidation of Te(II) in T1 to Te(IV) in T1•X2 results in the switch from aromaticity to nonaromaticity for the six‐membered telluropyran ring, as revealed by nucleus‐independent chemical shift calculations. It is also found that the halides in the halogen adducts can be exchanged by lighter ones, but not vice versa. The stabilities of the oxidized products are in the order of T1•Cl2>T1•Br2>T1•I2, which are consistent with the calculated rate constants and energy barriers of the elimination reactions.