Heteroleptic phthalocyaninato-[2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] rare earth(III) triple-deckers: synthesis and spectroscopic characterization

The homo-dinuclear heteroleptic phthalocyaninato-[2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] rare earth(III) triple-decker complexes (Pc)M[Pc(OC₈H₁₇)₈]M[Pc(OC₈H₁₇)₈] (M=Pr, Nd, Sm, Eu, Tb, Dy, Y, Ho, Er, Tm) (1a–10a) and (Pc)M[Pc(OC₈H₁₇)₈]M(Pc) (M=Nd, Sm, Eu, Tb, Dy, Y, Ho, Er, Tm) (2b–10b) were obtained by condensation of bis(phthalocyaninato) rare earths M[Pc(OC₈H₁₇)₈]₂ (M=Pr, Nd, Sm, Eu, Tb, Dy, Y, Ho, Er, Tm), Li₂(Pc) and M(acac)₃·nH₂O (M=Pr, Nd, Sm, Eu, Tb, Dy, Y, Ho, Er, Tm). These novel compounds were characterized by ¹H NMR, mass, electronic absorption (UV–Vis), and IR spectroscopic methods.     

Photophysical properties of Pr(III) and Er(III) complexes of poly(pyrazolyl)borates.

The complexes [M(L(1))(2)(NO(3))] and [M(L(2))(NO(3))(2)](M = Pr, Er; L(1)= the tetradentate ligand dihydrobis-[3-(2-pyridyl)pyrazolyl]borate; L(2)= the hexadentate ligand hydrotris-[3-(2-pyridyl)pyrazolyl]borate) were prepared and their structural and photophysical properties studied. All complexes are 10-coordinate. Crystallographic analysis of [M(L(1))(2)(NO(3))](M = Pr, Er) showed that for the smaller Er(iii) ions steric congestion at the metal centre results in two of the Er-N(pyridyl) distances being particularly long, which does not occur with the larger Pr(iii) ion that is better able to accommodate 10-fold coordination. On UV irradiation, both Pr(iii) complexes show, in the visible region of their luminescence spectra, transitions originating from both the (3)P(0) level (at ca. 21,000 cm(-1)) and the (1)D(2) level (at ca. 17,000 cm(-1)), a consequence of the fact that the lowest triplet state of the coordinated pyrazolylborate ligands lies at ca. 24,000 cm(-1) in each case so is high enough in energy to populate both levels. This contrasts with Pr(iii) complexes based on diketonate ligands in which the lower triplet energies of the ligands result in emission from the (1)D(2) level only. At longer wavelengths, near-infrared luminescence arising from the (1)D(2) emissive level is observed with lifetimes (in both the solid state and solution) being in the range 50-110 ns. For both Er(iii) complexes, luminescence at 1530 nm occurs following UV excitation of ligand-centred transitions. In CH(2)Cl(2) both complexes gave dual-exponential luminescence, with the major component having a lifetime characteristic of an intact Er(iii) complex (approximately 1.5 micros) and the minor component being much shorter lived (0.2-0.5 micros), suggestive of a species in which a ligand is partially detached and the metal is solvated, with the two forms interconverting slowly. This behaviour is consistent with the steric congestion and long M-N(pyridyl) bonds that were observed in [Er(L(1))(2)(NO(3))]. In the solid state both Er(iii) complexes gave very weak luminescence, which could be fitted to a single exponential decay with a lifetime similar to the longer-lived of the solution components.     

Near-infrared luminescent lanthanide (Er, Nd) complexes covalently bonded to a terpyridine-functionalized silica matrix.

New kinds of hybrid materials containing covalently bonded tris(dibenzoylmethanate)Ln complexes (Ln=Er, Nd) in a terpyridine-functionalized silica matrix have been prepared and their near-infrared luminescence properties reported.     

Synthesis and pH-sensitive luminescence of bis-terpyridyl iridium(III) complexes incorporating pendent pyridyl groups

A series of iridium(III) bis-terpyridine complexes have been prepared which incorporate pendent pyridyl groups at the 4′-positions of one or both of the terpyridine (tpy) ligands. These include: three mutually isomeric homoleptic complexes, in which the nitrogen atom of the pendent pyridyl is para, meta or ortho to the C-C bond to the terpyridine; their heteroleptic analogues in which the second ligand is 4′-tolyl-terpyridine (ttpy); analogous complexes of the new ligand, 4′-(2,6-dimethylpyrid-4-yl)-terpyridine; and related complexes incorporating an additional phenyl ring interposed between the terpyridine and the pendent pyridyl group. All of the complexes are luminescent in air-equilibrated aqueous solution at room temperature. The homoleptic complexes display structured emission resembling that of unsubstituted [Ir(tpy)₂]³⁺, with luminescence lifetimes of around 1 μs under these conditions. The heteroleptic analogues give broader, red-shifted emission spectra, similar to that of [Ir(ttpy)₂]³⁺, indicating that emission in these complexes arises primarily from a lower-energy excited state associated with the 4′-tolyl-terpyridine ligand. A further red-shift for the complexes incorporating the additional phenyl ring suggests that the emissive state involves the more conjugated phenylpyridyl-appended ligand in these cases. The luminescence of all of the heteroleptic complexes investigated, except the meta-substituted system, is sensitive to the protonation state of the pendent pyridyl group, and the structure of the ligand can have a significant influence on both the magnitude of the response and the pH region over which it occurs.     

Synthesis,density functional theory calculations and luminescence of lanthanide complexes with 2,6‐bis[(3‐methoxybenzylidene)hydrazinocarbonyl] pyridine Schiff base ligand

A pyridine‐diacylhydrazone Schiff base ligand, L = 2,6‐bis[(3‐methoxy benzylidene)hydrazinocarbonyl]pyridine was prepared and characterized by single crystal X‐ray diffraction. Lanthanide complexes, Ln–L, {[LnL(NO₃)₂]NO₃.xH₂O (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Er)} were prepared and characterized by elemental analysis, molar conductance, thermal analysis (TGA/DTGA), mass spectrometry (MS), Fourier transform infra‐red (FT‐IR) and nuclear magnetic resonance (NMR) spectroscopy. Ln–L complexes are isostructural with four binding sites provided by two nitro groups along with four coordination sites for L. Density functional theory (DFT) calculations on L and its cationic [LnL(NO₃)₂]⁺ complexes were carried out at the B3LYP/6–31G(d) level of theory. The FT‐IR vibrational wavenumbers were computed and compared with the experimentally values. The luminescence investigations of L and Ln–L indicated that Tb–L and Eu–L complexes showed the characteristic luminescence of Tb(III) and Eu(III) ions. Ln–L complexes show higher antioxidant activity than the parent L ligand.     

Microcalorimetric and spectroscopic investigation of the antibacterial properties of cationic ytterbium(III)-porphyrin complexes lacking charged peripheral groups

The antibacterial activities towards Escherichia coli of two cationic Yb(III)-monoporphyrin complexes, [Yb(III)(TMP)(H2O)3]Cl (1) and [Yb(III)(TTP)(H2O)3]Cl (2), were investigated at the cellular and sub-cellular levels. The biological effects of the complexes on the growth of E. coli were evaluated by microcalorimetry and by analysis of the resulting metabolic thermogenic curves, from which IC50 values and metabolic parameters such as growth rate and generation time were derived. At the subcellular level, DNA-binding experiments were performed by means of UV/VIS- and fluorescence-titration experiments, as well as by near-infrared (NIR) emission, which revealed that 1 and 2 strongly bind to herring-sperm DNA (HS-DNA), though by different binding modes.     

Half-sandwich Ru II[9]aneS3 complexes structurally similar to antitumor-active organometallic piano-stool compounds: preparation, structural characterization and in vitro cytotoxic activity

The preparation, structural characterization, and chemical behavior in aqueous solution of a series of new Ru[9]aneS3 half-sandwich complexes of the type [Ru([9]aneS3)Cl(NN)][CF3SO3] and [Ru([9]aneS3)(dmso-S)(N-N)][CF3SO3]2 (5-15, NN=substituted bpy or 2x1-methylimidazole) are described. The X-ray structures of [Ru([9]aneS3)Cl(3,3'-H2dcbpy)][CF3SO3] (9) (3,3'-H2dcbpy=3,3'-dicarboxy-2,2'-bipyridine), [Ru([9]aneS3)Cl(4,4'-dmobpy)][CF3SO3] (13) (4,4'-dmobpy=4,4'-dimethoxy-2,2'-bipyridine), and [Ru([9]aneS3)Cl(1-MeIm)2][CF3SO3] (15) (1-MeIm=1-methylimidazole) were also determined. The new compounds are structurally similar to anticancer-active organometallic half-sandwich complexes of formula [Ru(eta6-arene)Cl(NN)][PF6]. Three chloro compounds (5, 9, 15) were tested in vitro for cytotoxic activity against two human cancer cell lines in comparison with the previously described [Ru([9]aneS3)Cl(en)][CF3SO3] (1, en=ethylenediamine), [Ru([9]aneS3)Cl(bpy)][CF3SO3] (2), and with their common dmso precursor [Ru([9]aneS3)Cl(dmso-S)2][CF3SO3] (3). Only the ethylenediamine complex 1 showed some antiproliferative activity, ca. one order of magnitude lower than the reference organometallic half-sandwich compound RM175 that contains biphenyl instead of [9]aneS3. This compound was further tested against a panel of human cancer cell lines (including one resistant to cisplatin).     

Synthesis and high ranked NLT properties of new sulfonamide-substituted indium phthalocyanines

The synthesis and characterization of three new indium phthalocyanines bearing eight N-alkyl- or N-arylsulfonamide groups is described. The new compounds are {2,3,9,10,16,17,23,24-octakis[4-(4-methoxyphenylaminosulfonyl]phenoxy]phthalocyaninato}indium(III) chloride (7), {2,3,9,10,16,17,23,24-octakis[4-diethylaminosulfonyl)phenoxy]phthalocyaninato}indium(III) chloride (8) and {2,3,9,10,16,17,23,24-octakis[4-didodecylaminosulfonyl)phenoxy]phthalocyaninato}indium(III) chloride (9), and were obtained in 23-49% yields. The precursors of phthalocyanines 7-9 are sulfonamide-substituted phthalonitriles that can be prepared by reacting 4,5-bis(4-chlorosulfonylphenoxy)phthalonitrile (3) with amines. The nonlinear transmission (NLT) of complexes 7-9 was determined at 532 nm using ns pulses. All three phthalocyanines behave as reverse saturable absorbers with increasing efficiency of optical limiting in the order 7 < 8 < 9. A comparative analysis of the NLT results is attempted in terms of the structural differences in 7-9.     

Electrogenerated chemiluminescence from polymer-bound ortho-metallated iridium(III) systems.

Three ortho-metallated iridium complexes whose emission maxima fall in different regions of the electromagnetic spectrum were bound in either Nafion or poly(9-vinylcarbazole) and their electrogenerated chemiluminescence (ECL) reported. The reaction of F(Ir)pic [bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)-iridium III] with the oxidative-reductive co-reactant tri-n-propylamine (TPrA) resulted in ECL when the iridium complex was bound in Nafion. No significant ECL was observed for (btp)(2)Ir(acac) (bis[2,(2'-benzothienyl)-pyridinato-N,C3'](acetylacetonate)Ir(III)), and Ir(ppy)(3) (where ppy = 2-phenylpyridine) under these conditions. However, all three compounds displayed ECL with TPrA when bound in poly(9-vinylcarbazole).     

Bis[platinum(II)] and bis[platinum(IV)] complexes with optically active bis(vicinal-1,2-diamines) and their interaction with DNA.

Bis[platinum(II)] [Cl2Pt(LL)PtCl2] complexes 2,5 and 8 with chiral non-racemic ligands: 1a-c (LL = (R,R), (S,S) and (R,S) N,N'-bis(3,4-diaminobutyl)hexanediamide); 4a,b (LL = (R,R) and (S,S) N,N'-bis[3,4-bis(diaminobutyl)] urea); 7a-d (LL' = (R,R), (S,S), (R,S) and (S,R) 4,5-diamino-N-(3,4-diaminobutyl) pentanamide) and bis[platinum(IV)] complex 10-13 with ligands 1a,b and 4a,b have been prepared and characterized by IR, 1H, 13C and 195Pt NMR spectra. The interactions of 2a-c, 5a, 5b, 8a-d and 10a with dsDNA were investigated with the goal of examining whether the chirality, the nature of the spacer and the oxidation state have an influence on platinum-DNA binding properties. All the bis[platinum(II)] complexes form with dsDNA intra- and interstrand crosslinks and crosslinks over sticky ends, whereas the bis[platinum(IV)] complex 10a only forms intra- and interstrand crosslinks. The platinum-DNA coordination sites were determined by the T4 DNA polymerase footprinting method. The results show that all investigated bis(platinum) complexes have high preference towards distinct purines. All isomeric bis(amide) 2a-c and mono(amide) 8a-d complexes exhibit nearly the same binding pattern, whereas the ureide complexes 5a and 5b have other coordination sites with higher sequence preference. Interestingly, the ureides 5a and 5b differ in their coordination sites not only in comparison to the bis(amides) 2a-c and mono(amides) 8a-d, but also between each other. The bis[platinum(IV)] complex 10a also differs in coordination sites in comparison to all the bis[platinum(II)] compounds.     

Synthesis and DNA binding of mu-[2,9-bis(2-imidazo[4,5-f][1,10]phenanthroline)-1,10-phenanthroline]bis[1,10-phenanthrolinecopper(II)

A binuclear complex [(phen)Cu(mu-bipp)Cu(phen)](ClO(4))(4), where phen=1,10-phenanthroline and bipp=2,9-bis(2-imidazo[4,5-f][1,10]phenanthroline)-1,10-phenanthroline, has been synthesized and its interaction with calf-thymus DNA in the buffer containing 5mM Tris and 50mM NaCl has been studied by means of electronic absorption titration, luminescence titration and viscometric measurements. The absorbance of the complex in the range of 320-400 nm, which is mainly based on bipp showed no obvious change upon addition of DNA, while the peak at 270 nm, which is determined by both phen and bipp decreased by up to 18%. The emission band of the complex around 360 nm decreased remarkably in presence of DNA. The emission quenching of this complex by [Fe(CN)(6)](4-) was depressed greatly when bound to DNA. The relative viscosity of DNA was increased by this complex more significantly than a bipp directed intercalating reagent. These results suggest that this complex binds to calf thymus DNA by intercalation of the two phenanthrolinecopper terminals. The apparent intrinsic binding constant of the complexes with DNA was 1.6 x 10(4)M(-1) as determined by UV-visible titration.     

Structure and NIR luminescence of lanthanide(III) complexes with an organic tridentate ligand

Some lanthanide (Ln) complexes (Ln = Er, Nd, Yb) with an organic ligand, 6-diphenylamine carbonyl 2-pyridine carboxylic acid (HDPAP), have been synthesized. The crystal structure and near infrared luminescence of these complexes (Er-DPAP, Nd-DPAP and Yb-DPAP) have been investigated. The results showed that the lanthanide complexes have electroneutral structures and the near infrared (NIR) emission exhibits characteristic narrow emission of the lanthanide ions. The energy transfer mechanisms in the lanthanide complexes were discussed.     

Heteroleptic Cu(I) complexes containing phenanthroline-type and 1,1′-bis(diphenylphosphino)ferrocene ligands: Structure and electronic properties

Three new heteroleptic Cu(I) complexes containing one phenanthroline and one diphosphine type ligand ([Cu(N-N)(P-P)]⁺) have been prepared. In particular, one ligand is constituted by 1,10-phenanthroline (1), 2,9-dimethyl-1,10-phenanthroline (2) and 2,9-diphenethyl-1,10-phenanthroline (3) and the other ligand is in all cases 1,1′-bis(diphenylphosphino)ferrocene (dppf). Therefore, copper and iron metal centres are quite close one another, as evidenced by X-ray crystal diffraction. The structure together with the electrochemical and photophysical properties of these complexes have been compared to that of the corresponding complexes where dppf has been replaced by bis[2-(diphenylphosphino)-phenyl]ether (POP). Cyclic voltammetric experiments evidenced that the first oxidation process is located on the ferrocene moiety and that oxidation of Cu(I) is moved to more positive potential values and a chemical reaction is coupled to the electron transfer process. The absorption spectra show a metal-to-ligand charge transfer (MLCT) band, typical of Cu(I) phenanthroline complexes, at a higher energy compared to the homoleptic [Cu(N-N)₂]⁺ species. No emission at either room temperature or 77 K has been observed for compounds 2 and 3, contrary to the high luminescence observed for the corresponding POP complexes. This result is consistent with a photoinduced energy transfer from the Cu(I) complex to the ferrocene moiety.     

Visible‐near‐infrared luminescent lanthanide ternary complexes based on beta‐diketonate using visible‐light excitation

We used the synthesized dinaphthylmethane (Hdnm) ligand whose absorption extends to the visible‐light wavelength, to prepare a family of ternary lanthanide complexes, named as [Ln(dnm)₃phen] (Ln = Sm, Nd, Yb, Er, Tm, Pr). The properties of these complexes were investigated by Fourier transform infrared (FT‐IR) spectroscopy, diffuse reflectance (DR) spectroscopy, thermogravimetric analyses, and excitation and emission spectroscopy. Generally, excitation with visible light is much more advantageous than UV excitation. Importantly, upon excitation with visible light (401–460 nm), the complexes show characteristic visible (Sm³⁺) as well as near‐infrared (Sm³⁺, Nd³⁺, Yb³⁺, Er³⁺, Tm³⁺, Pr³⁺) luminescence of the corresponding lanthanide ions, attributed to the energy transfer from the ligands to the lanthanide ions, an antenna effect. Now, using these near‐infrared luminescent lanthanide complexes, the luminescent spectral region from 800 to 1650 nm, can be covered completely, which is of particular interest for biomedical imaging applications, laser systems, and optical amplification applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Intermolecular chiral recognition processes probed by chiroptical luminescence

Enantiopreferential energy transfer processes between dissymmetric lanthanide and transition metal complexes dissolved in acetonitrile are studied using chiroptical luminescence techniques. The energy donors (luminophores) in this study are a racemic mixture of Ln(dpa)3 (3-) complexes (where Ln = Eu3+ or Tb3+ and dpa = 2,6-pyridinedicarboxylate), and the energy acceptors (quenchers) are an enantiomerically-resolved population of Co(R,R-chxn)3 3+ (where R,R-chxn = trans-1R,2R-diaminocyclohexane) complexes. The luminophores are dissolved in acetonitrile as (NEt4)3[Ln(dpa)3] (where NEt(4) = tetraethlylammonium) and (NBu4)[Ln(dpa)3] (where NBu4 = tetrabutylammonium) salts. The unquenched luminescence lifetimes are reported for both Eu(dpa)3 (3-) and Tb(dpa)3 (3-) in acetonitrile over the range 263-333 K, and these results are compared to luminescence lifetimes in aqueous solution. Time-resolved chiroptical luminescence measurements of enantiopreferential quenching kinetics are reported for samples with Eu(dpa)3 (3-) and Co(R,R-chxn)3 3+ in acetonitrile over 263-333 K range. These results are analyzed using a phenomenological quenching kinetics model, and the results are compared to results in aqueous solution. These comparisons show that the overall Eu-Co luminescence quenching efficiency is reduced in acetonitrile vs. aqueous samples, because the salts of (NX4)3[Eu(dpa)3] are not completely dissociated in acetonitrile. However, the enantiopreference exhibited is identical in acetonitrile vs. aqueous solution.     

Development of a novel neodymium compound for in vivo fluorescence imaging.

We developed a novel fluorescent probe that contains the neodymium(III) complex moiety and fluorescein moiety. This probe can emit long-lived near-infrared luminescence derived from a Nd ion through excitation of the fluorescein moiety with visible light (lambda(ex) = 488 nm, lambda(em) = 880 nm, lifetime = 2.3 micros). These results indicate the possibility of the probe as a candidate for in vivo fluorescence molecular imaging.     

Heteroleptic phthalocyaninato-[tetra(15-crown-5)phthalocyaninato] lanthanides(III) double-deckers: Synthesis and cation-induced supramolecular dimerisation

A series of heteroleptic bisphthalocyaninates [(15C5)₄Pc]M(Pc) ((15C5)₄Pc = 2,3,9,10,16,17,24,25-tetrakis(15-crown-5)phthalocyaninate; Pc = unsubstituted phthalocyaninate; M = La, Sm, Dy, Tm) was synthesized. The raise-by-one-story method was applied in the cases of Sm, Dy and Tm complexes, whereas for the La complex we have developed a new synthetic approach. The complex [(15C5)₄Pc]La(Pc) is the first representative of heteroleptic lanthanum diphthalocyaninates. Homoleptic counterparts M[(15C5)₄Pc]₂ and M(Pc)₂, M = La, Sm, Dy, Tm have also been prepared for comparative studies. The UV-Vis spectral properties of all synthesized heteroleptic compounds were investigated and compared to those of the homoleptic unsubstituted and crown-substituted diphthalocyaninates. Cation-induced dimerisation of heteroleptic complexes was studied. The observed spectral effects were explained in terms of excitonic coupling between chromophoric molecules. The unsymmetrical distribution of electronic density over macrocyclic ligands is established.     

Reaction of monosubstituted hydrazines and diazenes with rat-liver cytochrome P450. Formation of ferrous-diazene and ferric sigma-alkyl complexes

The alkyldiazenes RN = NH (R = CH3 or C2H5) react with reduced microsomal cytochrome P450 leading to complexes exhibiting a Soret peak at 446 nm. Upon oxidation of the [cytochrome P450-Fe(II)(CH3N = NH)] complex with limited amounts of dioxygen, a new complex characterized by a Soret peak at 486 nm is formed. The latter complex was also formed upon slow reaction of methyldiazene with microsomal cytochrome P450-Fe(III) or in situ oxidation of methylhydrazine by limited amounts of O2 or ferricyanide. This complex is rapidly destroyed by O2 or ferricyanide in excess and more slowly by excess dithionite in the presence of CO. Reactions of ethyldiazene or benzyldiazene with cytochrome P450-Fe(III) afforded similar complexes characterized by Soret peaks around 480 nm. These results, when compared to those recently described on reactions of monosubstituted hydrazines RNHNH2 and diazenes RN = NH with hemoglobin and iron-porphyrins, are consistent with a [cytochrome P450-Fe(II)(RN = NH)] structure for the 446-nm-absorbing complexes and a sigma-alkyl cytochrome P450-Fe(III)-R structure for the complexes characterized by a Soret peak around 480 nm. They also suggest a sigma-cytochrome P450-Fe(III)-Ph structure for the complex derived from phenylhydrazine oxidation, recently described in the literature. Finally, they provide the first evidence that cytochrome P450-Fe(III)-R complexes are formed upon microsomal oxidation of alkyl or phenylhydrazines.     

Synthesis and properties of red emitter Ru(II) complexes based on 6,6′-disubstituted-4,4′-bipyrimidine

Heteroleptic complexes [Ru(bpy)₂(R₂bpm)]²⁺, where bpy = 2,2′-bipyridine and R₂bpm = 6,6′-diaryl-4,4′-bipyrimidine, have been synthesized and characterized, together with the homoleptic complex [Ru(R₂bpm)₃]²⁺, in which R₂bpm = 6,6′-diphenyl-4,4′-bipyrimidine. The substituent aryl on the bipyrimidine has significant effects on the properties of these complexes as compared to the parent [Ru(bpy)₂(bpm)]²⁺ complex. The complexes exhibit Ru-to-bpm charge transfer (CT) absorptions centered at about 540 nm and Ru-to-bpy CT absorptions centered at about 435 nm. The assignment of the low energy absorptions is supported by the relative ease of the reduction of the new complexes as compared to [Ru(bpy)₃]²⁺. The new complexes exhibit a relatively intense emission at room temperature, with lifetimes in the 10-50 ns range, with the homoleptic species exhibiting the higher-energy (maximum at 724 nm) and the longest-lived (τ = 48 ns) emission among the complexes. Luminescence lifetimes and quantum yields are governed by the energy gap law, indicating that direct deactivation to the ground state is the dominant relaxation pathway for 1-6, while thermally activated processes are inefficient.     

Synthesis, DNA-binding and photocleavage studies of cobalt(III) mixed-polypyridyl complexes: [Co(phen)(2)(dpta)](3+) and [Co(phen)(2)(amtp)](3+)

Two novel cobalt(III) mixed-polypyridyl complexes [Co(phen)(2)(dpta)](3+) and [Co(phen)(2)(amtp)](3+) (phen=1,10-phenanthroline, dpta=dipyrido-[3,2-a;2',3'-c]- thien-[3,4-c]azine, amtp=3-amino-1,2,4-triazino[5,6-f]1,10-phenanthroline) have been synthesized and characterized. The interaction of these complexes with calf thymus DNA was investigated by spectroscopic, cyclic voltammetry, and viscosity measurements. Results suggest that the two complexes bind to DNA via an intercalative mode. Moreover, these Co(III) complexes have been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365nm. The mechanism studies reveal that hydroxyl radical (OH()) is likely to be the reactive species responsible for the cleavage of plasmid DNA by [Co(phen)(2)(dpta)](3+) and superoxide anion radical (O(2)(-)) acts as the key role in the cleavage reaction of plasmid DNA by [Co(phen)(2)(amtp)](3+).