Singly and Doubly 1,2-Phenylene-Inserted Porphyrin Arch-Tape Dimers: Synthesis and Highly Contorted Structures

Abstract

Singly and doubly 1,2-phenylene-inserted Ni^II porphyrin arch-tape dimers 3 and 9 were synthesized from the corresponding β-to-β 1,2-phenylene-bridged Ni^II porphyrin dimers 5 and 11 via Ni⁰ -mediated reductive cyclization and DDQ/Sc(OTf)₃ -promoted oxidative cyclization as key steps, respectively. Owing to the fused eight-membered ring(s), 3 showed a more contorted structure than those of previously reported arch-tape dimers 2 a and 2 b possessing a fused seven-membered ring. Furthermore, 9 displayed much larger molecular contortion. As the molecular contortion increases, the Q band of the absorption spectrum becomes more red-shifted and the electrochemcial HOMO-LUMO gap becomes smaller, reaching at 1294 nm and 0.77 eV in 9, respectively. The effect of molecular contortion on the electronic properties was studied by means of DFT calculations.

Keywords: NIR-absorption; curved π-conjugated networks; eight-membered rings; phenylenes; porphyrinoids.