Synthesis,crystal structures,antioxidant activities,and DNA-binding studies of two silver(I) complexes with 1,3-bis(1-ethylbenzimidazol-2-yl)-2-thiapropane,and α,β-unsaturated carboxylates

Two new ternary complexes of silver(I) with 1,3-bis(1-ethylbenzimidazol-2-yl)-2-thiapropane (bebt) and two ·α,β-unsaturated carboxylates, [Ag(bebt)(crotonate)] (1) and [Ag(bebt)₂](o-coumarate)·CH₃CN·2C₂H₅OH (2), have been synthesized, and characterized by physicochemical and spectroscopic methods. Single-crystal X-ray diffraction revealed that the coordination environment of 1 can be described as trigonal planar, while 2 has a distorted tetrahedral geometry. Experimental studies of the DNA-binding properties indicated that the free ligand and both complexes bind to DNA via intercalation, and the order of the binding affinity is 1 > bebt > 2. Antioxidant activity experiments show that 2 possesses significant antioxidant activity against hydroxyl radicals, with more efficient hydroxy radical scavenging compared with mannitol and vitamin C.     

Synthesis,characterization, and antimicrobial activity of two Schiff base silver(I) complexes derived from 4-carboxybenzaldehyde

Two new Schiff base silver(I) complexes, {[Ag(L¹)][H₂O]}_∞ (1) and {[Ag(L²)][H₂O]}_∞ (2), where L¹ = 4-((2-diethylaminoethylimino)methyl)phenecarboxylate and L² = 4-([3-(morpholin-4-yl)propyl]iminomethyl)phenecarboxylate, have been synthesized and characterized. X-ray crystallographic analysis reveals that silver ions in 1 are bridged by L¹ to form a one-dimensional zigzag chain, while three silver ions in 2 are linked by L² to produce a two-dimensional coordination polymer. Guest water molecules in 1 generate a one-dimensional hydrogen-bonded chain. Both 1 and 2 offer high antibacterial activity against Gram-positive bacteria Staphylococcus aureus with MIC values of 0.26 and 0.24 mM and to exhibit good inhibitory activity against urease with the respective IC₅₀ values of 3.5 ± 0.1 and 3.8 ± 0.2 μM.     

Four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes with brightly luminescence properties

Three four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes, [Cu(Py-Im)(POP)](PF₆) (P1), [Cu(Py-BenIm)(POP)](PF₆) (P2), and [Cu(Py-c-BenIm)(POP)](PF₆) (P3) (Py-Im = 3-methyl-1-(pyridin-2-yl)-1H-imidazolylidene, Py-BenIm = 3-methyl-1-(pyridin-2-yl)-1H-benzo[d]imidazolylidene, Py-c-BenIm = 3-methyl-1-(pyridin-2-ylmethyl)-1H-benzo[d]imidazolylidene, POP = bis([2-diphenylphosphino]-phenyl)ether), have been synthesized without transmetalation of the NHC–Ag(I) complex for the first time. The photophysical properties of the resultant NHC–Cu(I) complexes have been systematically investigated via spectroscopic methods. All complexes exhibit good photoluminescence properties with long excited-state lifetimes and moderate quantum yields. Density functional theory and time dependent density functional theory calculations were employed to rationalize the photophysical properties of the NHC–Cu(I) complexes.     

Ag(I) and Zn(II) isonicotinate complexes: design,characterization, antimicrobial effect,and CT-DNA binding studies

Trinuclear Ag(I) (1) and dinuclear and mononuclear Zn(II) isonicotinate (2 and 3) complexes were prepared and characterized by X-ray crystallography, elemental analysis, IR spectroscopy, and thermal analysis. Single-crystal analysis of the Ag(I) complex reveals two different monodentate carboxylate coordination modes, protonated and deprotonated, respectively. IR spectra showed correlations between isonicotinate coordination modes and Δ(ν_as???ν_s)_IR values. In addition, the hydrogen bonds significantly influence a position of carboxylate absorption bands. Moreover, IC₅₀ and MIC data for bacteria, yeasts, and filamentous fungi were determined and the binding of Ag(I) and Zn(II) complexes to calf thymus DNA was investigated using electronic absorption, fluorescence, and CD measurements. Biological tests showed that the Ag(I) complex is more active than commercially used Ag(I) sulfadiazine against Escherichia coli. The fluorescence spectral results indicate that the complexes can bind to DNA through an intercalative mode. The Stern–Volmer quenching constants for investigated complexes obtained from the linear quenching plot are in the range of 1.67 × 10⁴–3.42 × 10⁴ M^?1.     

A disparate 3-D silver(I) coordination polymer of pyridine-3,5-dicarboxylate and pyrimidine with strong intermetallic interactions: X-ray crystallography,photoluminescence and antimicrobial activity

A polymeric silver(I) complex, [Ag₄(μ-pydc)₂(μ-pm)₂]_n (1) (pydc = pyridine-3,5-dicarboxylate and pm = pyrimidine), has been synthesized and characterized by elemental analysis, IR spectroscopy, thermal analysis, and single-crystal X-ray diffraction. X-ray crystallographic data of 1 revealed that pydc exhibits two different coordinaton modes that play a key role in the construction of the 3-D crystal network including Ag–carboxylate clusters in which close Ag–Ag distances exist. The magnitudes of close Ag–Ag interactions in second-order energy (E²) have been revealed by natural bond orbital analysis performed with single point energy calculation using the experimental geometry of 1. Furthermore, the luminescent properties of 1 show strong fluorescence with two emission maxima in the visible region. Also, 1 has antifungal activity on Candida albicans (MIC value, 4 μg mL^?1) and good antibacterial activity on micro-organisms (MIC value, 64–256 μg mL^?1).     

Synthesis,spectroscopic characterization,antimicrobial activity and crystal structure of silver and copper complexes of sulfamethazine

Silver(I) and copper(II) complexes of 4-amino-N-(4,6-dimethyl-2-pyrimidinyl) benzenesulfonamide (smz) have been synthesized and characterized by elemental analysis and infrared (IR), ¹H NMR, and UV–vis spectroscopy. [Ag(smz)(pyridine)] (1) crystallizes in monoclinic system with space group P2₁/c and Z = 4, while [Cu(smz)₂(pyridine)₂]·H₂O (2) crystallizes in triclinic system with space group P-1 and Z = 2. X-ray analysis revealed that silver in 1 is four-coordinate exhibiting distorted tetrahedral geometry, while copper in 2 is coordinated to six nitrogens leading to a highly distorted octahedral geometry. The molecular structures of both 1 and 2 are stabilized by N–H?O and C–H?π intermolecular and C–H?O intramolecular interactions. Water plays a significant role in crystal packing by forming strong N–H?O_water intramolecular as well as O_water–H?N intermolecular interactions in 2. The results of IR, UV–vis, ¹H NMR spectral data and thermal analysis for 1 and 2 suggest that the binding of silver and copper to the sulfonamidic nitrogen is in agreement with the crystal structure determination. Antimicrobial activities of silver (1) and copper (2) complexes of sulfamethazine are studied by the dilution method against Staphylococcus aureus and Escherichia coli strains.     

Synthesis,structural, electrochemical,and spectroscopic studies of some (diimine)ruthenium nitrile complexes

The syntheses of cationic ruthenium(II) complexes [Ru(Me₂-bpy)(PPh₃)₂RR?][PF₆]_x {Me₂-bpy = 4,4?-dimethyl-2,2?-bipyridine, (3) R = Cl, R? = N≡CMe, x = 1, (4) R = Cl, R? = N≡CPh, x = 1, (5) R = R? = N≡CMe, x = 2} and [Ru(Me₂-bpy)(κ²-dppf)RR?][PF₆]_x {dppf = 1,1?-bis(diphenylphosphino)ferrocene, (6) R = Cl, R? = N≡CMe, x = 1, (7) R = Cl, R? = N≡CPh, x = 1, (8) R = R? = N≡CMe, x = 2} are reported, together with their structural confirmation by NMR (³¹P, ¹H) and IR spectroscopy and elemental analysis, and, in the case of trans-[Ru(Me₂-bpy)(PPh₃)₂(N≡CCH₃)Cl][PF₆] (3), by X-ray crystallography. Electronic absorption and emission spectra of the complexes reveal that all complexes except 4 and 6 are emissive in the range 370–400 nm with 8 exhibiting an emission in the blue. Cyclic voltammetry studies of 3–8 show reversible or quasi-reversible redox processes at ca. 1 V, assigned to the Ru(II/III) couple.     

Structural and Spectroscopic Studies of [M((x)tu)4]+ Systems (M = Cu,Ag; (x)tu = (substituted) Thiourea)

In a low‐temperature redetermination of improved precision of the structure of [Cu(tu)₄]₂(SiF₆) (‘tu’ = thiourea, SC(NH₂)₂), Cu–S range between 2.3173–2.3433(8), < > 2.336(11) Å, with S–Cu–S 92.72(3)–118.75(12)°. The first structure determination of a 1:4 adduct of a silver(I) salt with a (substituted) thiourea ligand is also reported, for silver(I) nitrate with ‘ethylenethiourea’, (‘etu’ = SC(NHCH₂)₂), as a monohydrate [Ag(etu)₄](NO₃)·H₂O, wherein Ag–S range between 2.544–2.637(2), < > 2.59(4) Å, S–Ag–S 87.88–117.57(7)°. Bands in the far‐IR spectra of these compounds are assigned to ν(MS) modes, and the frequencies are compared with those predicted by previously established correlations between ν(MS) and the M–S bond length d(MS) for copper or silver complexes with tu or etu ligands.     

Synthesis,crystal structures,and photocatalytic properties of two 2D supramolecular silver(I) coordination polymers derived from bis(1,2,4-triazole) and aromatic dicarboxylate ligands

Two silver(I)-mixed ligand coordination polymers (CPs), {[Ag(L)(Hmip)]·H₂O} _n (1) and {[Ag(L)]·0.5(DCTP)·H₂O]} _n (2) (H₂mip = 5-methylisophthalic acid, H₂DCTP = 2,5-dichloroterephthalic acid, and L = 4,4′-bis(1,2,4-triazol-1-ylmethyl)biphenyl) have been hydrothermally synthesized and structurally characterized. Two CPs display 1D zigzag chain and linear chain structures, respectively. Furthermore, these 1D chains are extended into 2D supramolecular networks through hydrogen bonding interactions. The luminescence properties and photocatalytic behaviors of both CPs are reported.     

Asymmetric N-heterocyclic carbene benzimidazolium salts and their silver(I) complexes: potential as ionic liquid crystals

The synthesis and characterisation of a homologous series of monodentate benzimidazolium salts, 1–4 and their mononuclear silver(I)–NHC (where NHC = N-heterocyclic carbene) complexes, 5–8, are reported. The benzimidazolium salts were prepared from the N-alkylation of 1-methyl-benzimidazole with alkyl halides of varying carbon chain lengths. The mono silver(I)-NHC complexes, 5–8, were prepared by the reaction of the benzimidazolium salts with Ag₂O. All the synthesised compounds were fully characterised by ¹H-nuclear magnetic resonance (¹H-NMR), ¹³C-NMR and fourier-transform infrared (FTIR) spectroscopy. The molecular structures of compounds 3·PF₆, 4·PF₆, 7 and 8 were elucidated through single-crystal X-ray diffraction analyses. We postulate that the attachment of long alkyl chains to the heterocyclic core of 1-methyl benzimidazole could induce mesophase formation. The liquid crystalline behaviour of the benzimidazolium salts was investigated by polarised optical microscope and differential scanning calorimetry. Salts 3 and 4 were found to be thermotropic liquid crystals which exhibited a smectic A phase. However, upon complexation with silver(I) ions, all the Ag(I)–NHC complexes are found to be non-mesogenic.     

Synthesis,characterization and luminescent properties of copper(I) halide complexes containing biphenyl bidentate phosphine ligand

Copper(I) halide complexes having thermally activated delayed fluorescence (TADF) and phosphorescence have attracted much attention. Here, a series of four-coordinate dinuclear copper(I) halide complexes, [CuX(bpbp)]₂ (bpbp = 2,2′-bis(diphenylphosphino)biphenyl, X = I (1), Br (2) and Cl (3)), were synthesized, and their molecular structures and photophysical properties were investigated. The structural analysis reveals that two copper(I) centers are bridged by two halogen ligands to form a dinuclear structure with a four-membered Cu₂X₂ ring. These complexes exhibit yellow to blue emission in the solid state at room temperature and have peak emission wavelengths at 575–487 nm with microsecond lifetimes (τ = 6.2–19.8 μs) and low emission quantum yields (<0.01%). The emissions of 1–3 originate from MLCT, XLCT, and IL (intraligand) transitions. Three complexes displayed good thermal stability.     

Silver(I) complexes with halo-substituted cyanoanilines: synthesis,characterization and antibacterial activity

Four Ag(I) complexes, [Ag(L₁)₂](NO₃) (1), [Ag(L₂)(NO₃)] (2), [Ag(L₃)₃](NO₃) (3), and [Ag(L₄)₂](NO₃) (4), with ligands derived from halo-containing cyanoanilines (L₁ = 4-amino-3fluorobenzonitrile, L₂ = 4-amino-3-chlorobenzonitrile, L₃ = 4-amino-3-bromobenzonitrile, L₄ = 4-amino-2-bromobenzonitrile) were synthesized and characterized by C, H, and N elemental analysis, IR and ¹H NMR spectroscopy and single crystal X-ray diffraction. Complexes 1–4 crystallized in the triclinic space group C2/c, P2(1)/n, P-1 and C2/c, respectively. In 1 and 4, Ag⁺ is four-coordinate with L₁ or L₄ to form 1-D _∞{[Ag(L₁/L₄)₂]⁺} polymeric cations. In 2, Ag⁺ is three-coordinate by two L₂ ligands and one NO₃^? ligand to form a 1-D _∞{[Ag(L₂)(NO₃)]} zigzag chain. In 3, Ag⁺ is four-coordinate by L₃ to form a dinuclear [Ag(L₃)₃]⁺ cation. The NO₃^? is a 4-connector bridging group in 1 and 3 and a 5-connector bridging group in 2 and 4. The intermolecular hydrogen bonds and Ag?O weak interactions play important roles in forming 3-D networks of 1–4. The antibacterial activities for 1–4 were evaluated against Bacillus subtilis, Staphylococcus aureus and Escherichia coli with MTT method. The antibacterial results indicated that 2 showed the best inhibitory activity against the test bacterial strains, and was as potent as chloramphenicol.     

Tricarbonylrhenium(I) complexes with the N,6-dimethylpyridine-2-carbothioamide ligand: combined experimental and calculation studies

Abstract

A new series of tricarbonyl complexes of rhenium(I) in the “2 + 1” system with the bidentate ligand N,6-dimethylpyridine-2-carbothioamide ((CH₃)NC₅H₄-CS-NH-CH₃, MeLH(Me)_NS) and a monodentate ligand (halides Cl, Br, or I, and the pseudohalide NCS anion) was synthesized. The use of mixed ligands led to the formation of neutral tricarbonylrhenium(I) complexes [Re(CO)₃(MeLH(Me)_NS)X] (X = Cl, Br, I, NCS) (1–4). Single-crystal X-ray diffraction was used to determine the crystal structures of all four compounds and those results were compared with molecular structures obtained from DFT calculations using the PBE0/def2-TZVPD approach. The complexes were also characterized by spectroscopic (FT-IR, NMR, and UV–vis) and analytical (HPLC, TGA, EA, ESI-MS) techniques. IR and UV–vis spectra were also calculated by DFT and TD-DFT methods. The cytotoxicity of these complexes was estimated using human ovarian cancer cell lines (A2780 and A2780cis), cervical cancer cells (HeLa), and non-cancerous human embryonic kidney cells (Hek-293). The toxicity of most complexes was moderate or low toward cancer cell lines (IC₅₀ = 46–231 μM) and similar against non-cancerous cells (IC₅₀ = 41-121 μM). Only the complex with chlorido ligand remarkably inhibited growth of ovarian cancer cells (IC₅₀ = 3 and 12 μM for A2780 and A2780cis, respectively). The cytotoxicity of 1 was higher than that of cisplatin.     

Syntheses,Structures, and Properties of the Complexes [Ag(N∧S)n](X), N∧S = 1‐Methyl‐2‐(alkylthiomethyl)‐1H‐benzimidazoles,X = PF6 (n = 2) or PO2F2 (n = 1)

The complexes [Ag(η²‐N∧S)₂](PF₆), N∧S = 1‐methyl‐2‐(methylthiomethyl)‐1H‐benzimidazole, mmb (complex 1 ) or 1‐methyl‐2‐(tert‐butylthiomethyl)‐1H‐benzimidazole, mtb (complex 2 ), and [Ag(μ,η²‐mmb)(μ,η²‐O₂PF₂)] (complex 3 ) were synthesized and characterized by X‐ray crystallography. Long Ag–S (ca. 2.70 Å) and shorter Ag–N bonds (ca. 2.23 Å) are part of characteristically distorted tetrahedral coordination arrangements at the silver(I) ions in 1 and 2 . Unexpectedly, the comparison with the copper analogue [Cu(η²‐mmb)₂](PF₆) reveals a more tetrahedral and less linear coordination arrangement for the corresponding silver species. Compound 3 as obtained by hydrolysis of the PF₆ ion or by the use of AgPO₂F₂ exhibits bridging mmb and η²‐difluorophosphate ligands in a chain‐type structure.     

Copper(II) complexes of picolinamide incorporating both tricyanomethanido and 2-(aminomethyl)pyridine moieties

Reaction of picolinamide (pca) with potassium tricyanomethanide (tcm) and copper(II) perchlorate in 1-propanol gave [Cu(pca)₂(tcm)₂] (1a and 1b) while addition of 2-(aminomethyl)pyridine (2-ampy) provided [Cu(pca)(2-ampy)(tcm)](ClO₄) (2). These compounds have been characterized by IR, powder X-ray diffraction, single crystal X-ray diffraction, combustion analysis, and temperature-dependent magnetic susceptibility. Compound 1a crystallized in the monoclinic space group C2/c whereas 1b and 2 crystallized in the triclinic space group Pī. In 1a, the copper complexes stack alternately with semi-coordinated tcm ions creating layers, further stabilized by hydrogen bonding to neighboring layers. In 1b, the tcm ions are coordinated to complete the octahedral coordination sphere around the copper ions and form staggered layers parallel to the ab face diagonal. In 2, stacks of copper complexes form bilayers, held together by hydrogen bonding between tcm ions and amino groups, parallel to the a axis. Variable temperature magnetic susceptibility data were collected on 1 and 2 from 1.8–310 K. The data were fit to the Curie–Weiss law which showed no significant magnetic exchange as expected based upon the crystal structures [1 ? Curie constant = 0.419(2) emu-K/mol-Oe, θ = ?0.10(6)°; 2 – Curie constant = 0.438(1) emu-K/mol-Oe, θ = 0.05(3)°].     

Synthesis,crystal structure,in vitro anticancer and in vivo acute oral toxicity studies of tetramethylene linked bis-benzimidazolium salts and their respective dinuclear Ag(I)–NHC complexes

The proligands of the series tetramethylenebis(N-n-alkylbenzimidazolium bromide) (where n = 3–10) (1–8) as N-heterocyclic carbene (NHC) precursors have been prepared by reacting the initially synthesized N-n-alkyl benzimidazole with 1,4-dibromobutane in 2 : 1 M ratio. A reaction of Ag₂O with 1–8 resulted in the formation of Ag(I) complexes tetramethylenebis{(N-n-alkylylbenzimidazol-2-ylidene)silver(I)hexafluorophosphate} (9–16), respectively. All the synthesized compounds were characterized by FT-IR, ¹H NMR, ¹³C NMR, atomic absorption and elemental analysis. Single-crystal X-ray diffraction study on tetramethylenebis{(N-n-octylbenzimidazol-2-ylidene)silver(I)hexafluorophosphate} (14) has revealed that the complex exists as a dinuclear compound. All compounds were assessed for their antiproliferation test on human colorectal cancer cell line (HCT 116). Interestingly, increasing the n-alkyl chain length from n = 3 to 10 of the proligands and their respective complexes showed trends in increased cytotoxicity against human colon cancer cell line. Cytotoxicity data showed that tetramethylene linked bis-benzimidazolium salts and their respective dinuclear Ag(I)–NHC complexes can be useful therapeutic agents against colon cancer.     

Synthesis,characterization and luminescent properties of three-coordinate copper(I) halide complexes containing 2-(diphenylphosphino)biphenyl

Highly emissive three-coordinate copper halide complexes with a bidentate phosphine ligand have attracted attention. Here, a series of three-coordinate mono- and dinuclear copper halide complexes, [CuI(dpbp)₂] (1) and [CuX(dpbp)]₂ (dpbp = 2-(diphenylphosphino)biphenyl, X = Br (2), Cl (3)), were synthesized, and their molecular structures and photophysical properties were investigated. In the solid state, these complexes exhibit green photoluminescence with microsecond lifetimes (λ_max = 515–538 nm; τ = 11.8–19.1 μs) at 298 K. The emission of the complexes originates from the (σ + X) → π* transition. All three complexes displayed good thermal stability.     

Syntheses,crystal structures,and DNA-binding properties of two nickel(II) complexes with 1,3-bis(benzimidazol-2-yl)-2-oxapropane derivatives

[Ni(obb)(DMF)₂(H₂O)]·(Pic)₂·0.5DMF (1) and [Ni(Etobb)₂]·(Pic)₂·2DMF (2) (obb = 1,3-bis(benzimidazol-2-yl)-2-oxapropane, Etobb = 1,3-bis(1-ethylbenzimidazol-2-yl)-2-oxapropane, Pic = picrate) have been synthesized and characterized by physicochemical and spectroscopic methods. The structures of both complexes have been determined by X-ray single-crystal diffraction. The coordination geometries of 1 and 2 can be described as distorted octahedra. The interaction of the nickel(II) complexes with calf thymus DNA was investigated by electronic absorption, fluorescence spectroscopy, and viscosity measurements. The experimental results suggest that 1 and 2 bind to DNA in an intercalation mode, and their binding affinity for DNA follows the order 1 > 2. DNA-binding behaviors can be attributed to the large coplanar aromatic rings in the V-shaped ligand and steric hindrance.     

Synthesis,crystal structures,and magnetic properties of three new iron(II) complexes with pyrrolyl-substituted triaryltriazoles

Three pyrrolyl-substituted triaryltriazoles, 3-(N-methyl-2-pyrrolyl)-4-(p-R-phenyl)-5-(2-pyridyl)-1,2,4-triazole (L¹: R = MeO; L²: R = Cl; L³: R = Br), and their mononuclear iron(II) complexes, trans-[Fe(L^1–3)₂(NCS)₂]?2MeOH (1: L¹; 2: L²; 3: L³), have been synthesized and characterized by elemental analysis, FT-IR, ESI-MS, and single-crystal X-ray crystallography. Crystallographic studies revealed that 1–3 are isomorphous and crystallize in the triclinic space group P-1. All the complexes have a similar octahedral [FeN₆] core with two trans-NCS^? ions. Each ligand adopts a chelating bidentate coordination mode via the pyridyl N and one N of the triazole. Intermolecular O–H?O hydrogen bonding and C–H?π interactions link the molecules of 1–3 to form a 1-D chain or 2-D framework. Variable-temperature magnetic susceptibility measurements indicated that all the complexes remained in a high-spin state from 1.8 to 300 K and had a weak antiferromagnetic interaction.     

Copper(I)-1,1,1-tris(diphenylphosphinomethyl)ethane complexes with different coordination modes tuned by auxiliary ligands and their spectroscopic properties

Three mono-, bi- and tetranuclear copper(I) complexes, [Cu(phen)(triphos-O)]BF₄ (1) (phen = 1,10-phenanthroline, triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane), [Cu₂(bipy)(triphos)₂](BF₄)₂ (2) (bipy = 4,4′-bipyridine), and [Cu₄(MeOC^N^N)₄(triphos)₂(bipy)](BF₄)₄ (3) (MeOC^N^N = 6-(4-methoxyphenyl)-2,2′-bipyridine), have been synthesized and characterized by NMR spectroscopy, electrospray ionization, and matrix-assisted laser desorption ionization time-of-flight mass spectrometries, elemental analysis, and X-ray crystal analysis. The crystal structure investigation revealed the copper ions of the complexes have pseudo-tetrahedral coordination geometry. The electronic absorption spectra of 1, 2, and 3 contain low-energy bands at 350–500 and 400–650 nm, which are assigned to d(Cu) → π*(phen or bipy) and a mixture of d(Cu) → π*(MeOC^N^N) and d(Cu) → π*(bipy) transitions, respectively. Complex 2 displays a strong, long-lived solid-state emission with a maximum at 555 nm and lifetime of 13.6 μs at room temperature. Photoinduced electron-transfer properties of 2 and 3 involving nanosecond time-resolved absorption spectroscopy and electron spin resonance techniques were studied.