A MLCT-switched photochromic copper(II) coordination polymer with 1,2-bis(2′-methyl-5′-(4″-pyridyl)-3′-thienyl)perfluorocyclopentene in crystalline phase

A novel Cu(II) coordination polymer with photochromic 1,2-bis(2′-methyl-5′-(4″-pyridyl)-3′-thienyl)perfluorocyclopentene (BM-4-PTP) was prepared and crystallographically characterized. Its photochromic behavior as well as magnetic property was investigated in crystalline phase. In complex [Cu(BM-4-PTP)Br2(DMF)2] (1), each copper atom is bridged by two N atoms of BM-4-PTP, two Br atoms from anions and two O atoms of DMF in an slightly distorted octahedral geometry. The basal planar center is in turn linked by bidentate ligand forming a 1-D polymeric chain. Free ligand showed typical spectral changes upon appropriate optical excitation, indicating the reversible photochromism in crystalline phase. Complex 1 occurred reversible photoisomerization not only through the π–π∗ transition but also the MLCT transition in crystalline phase. On the other hand, the magnetic property of complex 1 has been investigated by means of ESR. The spectra slightly and reversibly changed in response to UV and visible light supporting the normal photoreactivity in crystalline phase.

Graphical abstractThe complexation of CuBr2 with photochromic BM-4-PTP in DMF generated a novel coordination polymer [Cu(BM-4-PTP)Br2(DMF)2] (1). The metal free ligand displayed typical photochromic reactivity in crystalline phase. Complex 1 underwent photoisomerization not only through the π–π∗ transition but also the MLCT transition. In addition, the ESR spectra slightly and reversibly changed along photoirradiation in crystalline state.Figure optionsDownload full-size imageDownload as PowerPoint slide