N-Methyl-4-pyridinium Tetrazolate Zwitterion-Based Photochromic Materials.

N,N '-Disubstituted bipyridinium (viologen) and N-monosubstituted bipyridinium compounds are well known for their electron-transfer (ET) photochromic behavior. Their modification has exclusively focused on the N-substituents to date. For the first time, we have studied the photochromic behavior when one pyridyl ring of the bipyridinium is substituted with a multifunctional azole group, and have found that two new coordination compounds based on N-methyl-4-pyridinium tetrazolate (mptz) zwitterion, [Zn(mptz)(2)Br-2] (1) and [Cd-3(mptz)(2)Cl-6](n)center dot 4nH(2)O (2), exhibit typical ET photochromic behavior owing to photoinduced ET from halogen anion to the mptz ligand. This work demonstrates a new simple, neutral photoactive molecule with electron-accepting ability, which may act as a photoactive component for materials with potential photoswitching and photocatalysis applications.