Tamotsu Sugimori

Structural evidence for the intramolecular charge-transfer interaction involving an indole ring in ternary copper(II) complexes with L-tryptophan and aromatic diamines

Abstract With a view to understanding the precise binding mode and strength of the stacking interaction in the ternary copper(II) complexes comprising an aromatic diamine such as 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) and an aromatic amino acid such as L -phenylalanine, L -tyrosine and L -tryptophan ( L -trp), the crystal structure of [Cu(bpy)( L -trp)]ClO 4 and the circular dichroism (CD) and absorption spectra of [Cu(bpy)( L -trp)]ClO 4 and [Cu(phen)( L -trp)]ClO 4 have been investigated. The complex [Cu(bpy)( L -trp)]ClO 4 crystallizes in the monoclinic space group, P 2 1 , with two molecules in a unit cell of dimensions a =13.022(1), b =7.753(1), c =10.533(1) A, and β=91.18(1)°. The Cu(II) ion is five-coordinate square-pyramidal, with the two nitrogen atoms of bpy and the nitrogen and oxygen atoms of the amino acid coordinated at the equatorial positions in a slightly distorted square-planar form and the carboxylate oxygen atom of the neighboring molecule at the axial position. The most interesting structural feature of the complex is the existence of the intramolecular stacking interaction between the aromatic rings of L -trp and bpy with the average spacing of 3.67 A from the vacant axial position. The CD spectra in the d-d region for [Cu(bpy)( L -trp)ClO 4 and [Cu(phen)( L -trp)]ClO 4 in aqueous solution showed a large negative peak at 587 and 598 nm, respectively, and the magnitudes were greatly reduced in dioxane-water, which indicates that the aromatic ring stacking interaction is weakened in a hydrophobic environment. The absorption bands due to the charge transfer (CT) interaction between the indole ring and the aromatic diamine have been observed in the difference spectra in the near ultraviolet region. The strength of the stacking interactions has been demonstrated by the CT band intensity and the distance between the stacked rings to be in the order [Cu(phen)( L -trp)]ClO 4 >[Cu(bpy)( L -trp)]ClO 4 both in solution and in the solid stare.

Bathochromic shift of the Q-bands of octakis(p-t-butylbenzyloxy)phthalocyanines with magnesium(II), nickel(II) and copper(II) in a solvent mixture of chloroform and acetic acid

1,4,8,11,15,18,22,25-octakis(p-t-butylbenzyloxy)phthalocyanine complexes of magnesium(II), nickel(II) and copper(II) were prepared by refluxing the propanol solution of 3,6-di(p-t-butylbenzyloxy)phthalonitrile in the presence of magnesium turnings. The complexes showed intense Q-bands between 740 and 750 nm in chloroform. The magnesium(II) complex showed an additional weak band at 807 nm in chloroform, while the nickel(II) and copper(II) did not. The Q-band of the magnesium(II) species was red-shifted with increase of acetic acid in the solvent mixture of chloroform and acetic acid; 745, (765, 807) and (810, 868 nm) in chloroform, 0.1% (v/v) acetic acid and 60% (v/v) acetic acid, respectively. The magnesium(II) complex has bands at 900 and 999 nm in trifluoroacetic acid. In the solvent mixture of 1% (v/v) acetic acid, the red-shift of the Q-band was larger for the magnesium(II) derivative, a little for the nickel(II) and scarcely for the copper(II), respectively. The shift was explained by protonation of the external nitrogen atoms of the phthalocyanine ring.

Synthesis, spectral and electrochemical properties of a novel phosphorous(V)-phthalocyanine

A novel phosphorous(V)-phthalocyanine, [P(tppc)(OH)(O)], where tppc denotes tetrakis{(2′,6′-dimethyl)phenoxy}phthalocyaninate, has been synthesized and its spectral properties in non-aqueous and aqueous media have been investigated. This compound has been found free from aggregation in EtOH whereas forms J-aggregates in CH2Cl2 and acetonitrile, suggesting the presence of chemical interaction between the axial ligand and the surrounding solvent molecules. The most intense absorption band (Q-band) appears at 683 nm in EtOH, however, reaction with CF3COOH has given rise to a large red shift of the Q-band without lowering of its C4 symmetry (evidenced by magnetic circular dichroism spectroscopy), indicating protonation at the axial site. Its fluorescence quantum yield has been determined (0.49 in EtOH) and has been found much higher than those of the known SbV or AsV derivatives by more than one order of magnitude. The first reduction potential has been determined by cyclic voltammetry (-1.09 V vs. ferroceniu...