Dynamic structural change of a twisted hexaporphyrin complex by highly specific molecular recognition

The highly specific molecular recognition of a twisted hexaporphyrin complex, tris[5,5'-bis[5,10,15-tris{methoxy-(ethoxy)(2)carbonylethyl}porphyrinatozinc(II)]-2,2'-bipyridine]ruthenium(II) chloride (2), is described. Complex 2 has two trisporphyrin binding sites and can bind two triamines, tris(2-aminoethyl)amine (3) (K-1 = 3.0 x 10(8) M-1, K-2 = 3.0 x 10(7) M-1), 1,1,1-tris(aminomethyl)ethane (4) (K-1 = 2.0 x 10(7) M-1, K-2 = 1.4 x 10(6) M-1), tris(3-aminopropyl)-amine (5) (K-1 = 3.5 x 10(6) M-1, K-2 = 6.0 x 10(6) M-1), and 1,3,5-tris(aminomethyl)benzene (6) (K-1 = 2.9 x 10(6) M-1, K-2 = 1.2 x 10(6) M-1), strongly with its torsional motion. The 1:2 complex between 2 and the best fit triamine 3 showed the nature of the specific rigid structure in the UV-vis, fluorescence, and H-1 NMR spectra and isothermal titration calorimetry (ITC) measurements.