Thermal Reaction Behavior of Triphenylimidazolyl Radical with a Bulky Substituent

The triphenylimidazolyl radical (TPIR) is generated by the irradiation of the photochromic molecule hexaarylbiimidazole (1,2'-HABI). Usually, the unsubstituted TPIRs form 1,2'-HABI thermally at room temperature. In this study, we report the thermal reaction behavior of TPIR with a tBu group (tBu-TPIR) under N₂ atmosphere and the novel reactivities of TPIRs. Under N₂ atmosphere at room temperature, tBu-TPIRs form SpI with a spiro carbon and a novel HABI isomer tBu-1,4'-HABI, whose bonding pattern is different from that of the original unsubstituted HABI (1,2'-HABI). The results of ¹H NMR spectroscopy, EPR measurements, and DFT calculations revealed that SpI is generated via three steps: (1) intramolecular hydrogen transfer from the tBu group to the nitrogen atom of the imidazole ring, (2) intramolecular cyclization of alkyl radicals, and (3) intermolecular hydrogen transfer with another tBu-TPIR. Furthermore, we found that the thermal reaction of tBu-TPIR at a low temperature affords the diastereomers of other isomers (tBu-4,4'-HABI_RS and tBu-4,4'-HABI_RR); in other words, the thermal reaction of tBu-TPIR depends on temperature.

Electrochemical topological transformation of polysiloxanes

Coupling reactions between polymers are an important class of chemical modifications for changing, enhancing, and tuning the properties of polymeric materials. In particular, transformation of polymer topologies based on efficient, facile and less wasted coupling reactions remains a significant challenge. Here, we report coupling reactions based on electrochemical oxidation of 2,4,5-triphenylimidazole into a 2,4,5-triphenylimidazolyl radical and its spontaneous dimerization into hexaarylbiimidazole. Based on this chemistry, electrochemical topological transformation (ETT) and electrochemical chain extension have been realized with siloxane-based oligomers and polymers. Moreover, this approach enables one step ETT of star-shaped poly(dimethyl siloxane)s (PDMSs) into network PDMSs, running in an ionic liquid solvent and requiring no purification steps.

Synthesis of reversibly photocleavable pseudo-ladder polymers

Pseudo-ladder polymers composed of stiff ladder and reversibly photocleavable backbone linkages and their graft copolymers have been synthesized. Micelles constructed from the graft copolymers exhibited growth in their sizes upon photoirradiation.

Toward bidirectional photoswitchable colored photochromic molecules with visible light stability

Novel bidirectional photoswitchable colored photochromic [2]rotaxanes were fabricated, whose colored states exhibit considerable visible-light stability and high thermal stability. These features are crucial for photochromic molecules to be applied in information displays and data storage.

Pressure effects on the radical-radical recombination reaction of photochromic bridged imidazole dimers

The bridged imidazole dimers are some of the attractive fast photochromic compounds which have potential applications to the ophthalmic lenses, real-time hologram and molecular machines. The strategy for expanding their photochromic properties such as the colour variation and tuning the decolouration rates has been vigorously investigated, but the insight into the structural changes along the photochromic reactions has not been demonstrated in detail. Here, we demonstrated the pressure dependence of the radical-radical recombination reaction of the bridged imidazole dimers. The radical-radical interaction can be controlled by applying high pressure. Our results give fundamental information about the molecular dynamics of the bridged imidazole dimers, leading to the development of new functional photochromic machines and pressure-sensitive photochromic materials.