RESUMO
Based on two new bisthienylethenes containing N,O-donor binding sites, 2-(2-hydroxy-5-bromo-phenyl)-4,5-bis(2,5-dimethyl(3-thienyl))-1H-imidazole (BrLH) and 2-(2-hydroxy-5-diethylphosphono-phenyl)-4,5-bis(2,5-dimethyl(3-thienyl))-1H-imidazole (PLH), multifunctional mononuclear complexes Co(BrL)2·3CH3OH (1) and Co(PL)2·2CH3OH (2) have been synthesized and characterized by crystallographic analysis. In the molecular structures of 1 and 2, the Co(II) ion adopts a distorted tetrahedral coordination geometry, and is coordinated by two nonequivalent bisthienylethene molecules (BrL− in 1, PL− in 2), showing non-photoactive parallel and photoactive antiparallel conformations, respectively. Compounds 1 and 2 show a distinct distortion of Co(II) coordination geometry, with bond angles of NCoN = 112.71(12)° and OCoO = 99.87(11)° for 1 and NCoN = 119.93(12)° and OCoO = 107.31(13)° for 2. Thus, 1 and 2 revealed different magnetic behaviors, which are demonstrated by the χMT vs. T plots, and the frequency dependence of the χ'M and χ''M signals at low temperature. Besides the field-induced slow magnetic relaxation, both 1 and 2 also showed photochromic behavior. Upon irradiation with 360 nm light for 1 and 343 nm light for 2, their CH2Cl2CH3CN solutions could change color from being nearly colorless to blue purple. It was demonstrated that the substituent groups of Br atom and PO(OEt)2 in 1 and 2, respectively, could significantly influence their crystal structures, magnetic relaxations and photochromic properties.
RESUMO
Two bisthienylethenes 2-(2-hydroxyphenyl)-4,5-bis[2,5-dimethyl(3-thienyl)]-1H-imidazole (L1H) and 2-(2-hydroxyphenyl)-4,5-bis(2,5-dimethyl(3-thienyl))-1-phenyl-imidazole (L2H), which have a chelating N,O-donor binding site attached to the photochromic core, have been synthesized using a one-pot condensation reaction, and used to prepare the heteroleptic complexes [Ir(dfppy)2(L1)]·2CH3OH (1) and [Ir(dfppy)2(L2)] (2) [dfppyH = 2-(2,4-difluorophenyl)-pyridine]. In the crystal structures of all four compounds, two thiophene groups of each bisthienylethene molecule adopt parallel conformation. Neighboring molecules in L1H and 1 are linked into supramolecular chains through hydrogen bonds. Particularly, the packing structure of 1 contains right- and left-handed 21 helical chains. In contrast, neighboring molecules in L2H and 2 interact only through van der Waals interactions. At room temperature, L1H and L2H in CH2Cl2 show fluorescence emission at 442 nm and 469 nm, respectively. Compounds 1 and 2 in CH2Cl2 reveal broad emission band characteristics of the Ir(III)/dfppy(-) chromophores at 508 nm and 494 nm, respectively, with a mixing of (3)MLCT and (3)LC characters. At room temperature, the photochromism ability of L2H in CH2Cl2 is clearly weaker than that of L1H. Moreover, no photochromism has been observed in 1 and 2. It has been demonstrated that both the substituent group and {Ir(dfppy)2}(+) coordination could significantly influence the crystal structures, luminescence and photochromic properties of L1H, L2H, 1 and 2.