Novel arene RuII complexes containing 2,2’‐azobispyridine ligands were synthesized and characterized by using 1H and 13C NMR spectroscopy, UV/vis spectroscopy, electrochemistry, DFT calculations and single‐crystal X‐ray diffraction. Z‐configured complexes featuring unprecedented seven‐membered chelate rings involving the nitrogen atom of both pyridines were isolated and were shown to undergo irreversible isomerization to the corresponding E‐configured five‐membered chelate complexes in response to light or electrochemical stimulus.

Although side-chain polyazobenzenes have been extensively studied, main-chain polyazobenzenes (abbreviated MCPABs) are rarely reported due to the challenges associated with difficulty in synthetic chemistry and photoisomerization of azo bonds in MCPABs. Thus, it is highly demanded to develop new mechanisms other than photoisomerization of azo bonds in MCPABs to extend their applications. In this work, we created a new series of N-linked MCPABs via fast NaBH 4 -mediated reductive coupling polymerization on N-substituted bis(4-nitrophenyl)amines. The structure of MCPABs has been characterized by comprehensive solid-state NMR experiments such as CPMAS 13 C NMR with long and short contact times, cross-polarization polarization-inversion (CPPI), and cross-polarization nonquaternary suppressed (CPNQS). The azo bonds in MCPABs were found to be promising for acid vapor sensing, being acidified to form azonium ion with significant color change from red to green. And the azonium of MCPABs turned from green to red when exposed to base vapor, thus suitable for base vapor sensing.