Mesoporous TiO2 Beads Offer Improved Mass Transport for Cobalt‐Based Redox Couples Leading to High Efficiency Dye‐Sensitized Solar Cells

Overcoming ionic diffusion limitations is essential for the development of high‐efficiency dye‐sensitized solar cells based on cobalt redox mediators. Here, improved mass transport is reported for photoanodes composed of mesoporous TiO₂ beads of varying pore sizes and porosities in combination with the high extinction YD2‐o‐C8 porphyrin dye. Compared to a photoanode made of 20 nm‐sized TiO₂ particles, electrolyte diffusion through these films is greatly improved due to the large interstitial pores between the TiO₂ beads, resulting in up to 70% increase in diffusion‐limited current. Simultaneously, transient photocurrent measurements reveal no mass transport limitations for films of up to 10 μm thickness. In contrast, standard photoanodes made of 20 nm‐sized TiO₂ particles show non‐linear behavior in photocurrent under 1 sun illumination for a film thickness as low as 7 μm. By including a transparent thin mesoporous TiO₂ underlayer in order to reduce optical losses at the fluorine‐doped tin oxide (FTO)‐TiO₂ interface, an efficiency of 11.4% under AM1.5G 1 sun illumination is achieved. The combination of high surface area, strong scattering behavior, and high porosity makes these mesoporous TiO₂ beads particularly suitable for dye‐sensitized solar cells using bulky redox couples and/or viscous electrolytes.     

Complexation of Group IIIA metals with asymmetric tridentate ligands: Synthesis, characterization, formation constants and cytotoxicity

A series of new aluminum(III), gallium(III) and indium(III) complexes with some tridentate Schiff base, viz., N-{pyridine-2-ylmethyl}-2-hydroxy-5-methoxy-benzylideneamine [HL¹], N-{pyridine-2-ylmethyl}-2-hydroxy-benzylideneamine [HL²], N-{pyridine-2-ylmethyl}-2-hydroxy-5-nitro-benzylideneamine [HL³], N-{pyridine-2-ylmethyl}-2-hydroxy-5-bromo-benzylideneamine [HL⁴], N-{pyridine-2-ylethyl}-2-hydroxy-5-methoxy-benzylideneamine [HL⁵], N-{pyridine-2-ylethyl}-2-hydroxy-benzylideneamine [HL⁶], N-{pyridine-2-ylethyl}-2-hydroxy-5-nitro-benzylideneamine [HL⁷], N-{pyridine-2-ylethyl}-2-hydroxy-5-bromo-benzylideneamine [HL⁸], with the general formula [ML₂][Y] (M = Al³⁺, Ga³⁺, In³⁺; Y = NO₃⁻, ClO₄⁻) were synthesised and characterized by elemental analysis, ¹H NMR, FT-IR, UV-Vis spectrophotometry and mass spectrometry. The thermodynamic formation constants of the complexes were determined spectrophotometrically at constant ionic strength (I = 0.10 M NaClO₄) and at 25 °C in methanol. The trend of formation constants of the complexes are as follow:

Al<Ga<In     

Synthesis and characterization of nanocrystalline zinc sulfide via zinc thiobenzoate-lutidine single-source precursor

ZnS nanocrystals were prepared both in the form of mesoporous powder and thin films by one step thermal decomposition technique from a single-source procure (SSP) [Zn(SOCPh)₂Lut₂·H₂O]. The final product was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), N₂ adsorption-desorption isotherm, UV-Vis absorption spectroscopy and photoluminescence (PL) study. Structural analyses of the prepared ZnS revealed the formation of cubic crystallites with diameters around 5 and 10 nm for the thin films and powder materials, respectively. On the other hand, the powder form showed mesoporous nature (type IV isotherm) with an average pore diameter of 37.9 Å and BET specific surface area of 51.73 m²/g.     

Interfacial electron transfer on TiO2 sensitized with an axially anchored trans tetradentate Ru(II) compound

The ruthenium complexes, trans-[Ru(phen-NH-phen)(eina)₂](PF₆)₂ and trans-[Ru(phen-NH-phen)(ina)₂](PF₆)₂ where phen-NH-phen = N,N-bis(1,10-phenanthroline-2-yl)amine, ina = isonicotinic acid and eina = ethyl isonicotinate, have been synthesized and characterized by ¹H NMR, elemental analysis, and IR spectroscopy. The compounds were non-emissive at room temperature, but displayed intense photoluminescence in 4:1 ethanol/methanol glasses at 77 K with corrected emission maximum at 570-580 nm. A quasi-reversible wave observed in cyclic voltammetry experiments was assigned to the Ru^III/II couple, E° (trans-[Ru(phen-NH-phen)(eina)₂)^3+/2+ = +1.22 V versus Ag/AgCl. The trans-[Ru(phen-NH-phen)(ina)₂](PF₆)₂ compound was found to bind to nanocrystalline TiO₂ thin films from acetonitrile solution. Pulsed 532 nm excitation of trans-[Ru(phen-NH-phen)(ina)₂](PF₆)₂ anchored to mesoporous nanocrystalline TiO₂ thin films resulted in an absorption difference spectra consistent with the formation of an interfacial charge separated state trans-[Ru^III (phen-NH-phen)(ina)₂]⁺/TiO₂ (e⁻). The formation of this state could not be time resolved, consistent with rapid excited state injection into the TiO₂, k_inj > 10⁸ s⁻¹. Comparative measurements with a thin film actinometer yielded an injection quantum yield (?_inj) of 0.8. Charge recombination required milliseconds for completion and followed a bi-second-order equal concentration kinetic model with k₁ = 1.0 × 10⁸ s⁻¹, and k₂ = 3.0 × 10⁵ s⁻¹. In regenerative solar cells with 0.5 M LiI and 0.005 M I₂ in acetonitrile, incident photon-to-current efficiencies were typically less than 10%.     

Synthesis of an amphiphilic ruthenium complex with swallow-tail bipyridyl ligand and its application in nc-DSC

An amphiphilic swallow-tail bipyridyl ligand, 4,4′-bis(dihexylmethyl)-2,2′-bipyridine, and its heteroleptic ruthenium (II) complex were synthesized starting from dichloro-(p-cymene)ruthenium (II) dimer. The complex was characterized by UV/Vis and FTIR spectrophotometers, NMR spectroscopy and cyclic voltammetry. The performance of this complex as charge transfer photosensitizer in nc-TiO₂ based dye sensitized solar cells was studied under standard AM 1.5 sunlight and by using an electrolyte consisting of 0.6 M N-methyl-N-butyl imidazolium iodide (BMII), 0.1 M LiI, 0.05 M I₂, 0.5 M 4-tert-butyl pyridine (TBP) in acetonitrile. The complex, CS9 in DMF, gave a photocurrent density of 12.62 mA/cm², 630 mV open circuit potential and 0.62 fill factor yielding 5.68% efficiency.     

Efficient sensitization of nanocrystalline TiO2 films with high molar extinction coefficient ruthenium complex

A novel heteroleptic polypyridine ruthenium complex, cis-Ru(L1)(L2)(NCS)₂, L1 = 4,4′-dicarboxylic acid-2,2′-bipyridine (dcbpy), L2 = 4,4′-bis[p-diethylamino]-α-styryl]-2,2′-bipyridine, was synthesized. The dye displays extremely high molar extinction coefficient, which is comparable with organic dye. Preliminary test shows the dye-sensitized TiO₂ solar cell gives high conversion efficiency up to 8.65% under 1 Sun, while 8.35% is given for N3 based DSCs under the same condition. The dye will be further employed in solid state DSCs with hole transport material.     

Key aspects of individual layers in solid-state dye-sensitized solar cells and novel concepts to improve their performance

In this feature article, we discuss the key aspects of solid-state dye-sensitized solar cells (SDSC) and propose different concepts based on extensive studies carried out in our group to improve their performance. The influence of compact TiO₂ layer, novel donor-antenna sensitizing dyes, nature of nanocrystalline-TiO₂ layers and solid-state organic hole conductors on the performance of SDSC is discussed in this article. Both preparation and thickness of the compact TiO₂ layer were optimized using spray pyrolysis. The studies revealed that an optimum film thickness of 120-150 nm of compact TiO₂ yielded the best rectifying behavior and SDSC performance. The influence of three different mesoporous titania films, obtained from three different titania nanocrystals, prepared by sol-gel, thermal, and colloidal-microwave process, was also studied and discussed here. The TiO₂ layer with the optimum pore volume and pore diameter (∼44 nm) displayed the highest efficiency and IPCE in SDSC. The importance of pore size rather than high surface area for filling the mesoporous layer with solid-state hole conductor became evident from this study. A series of heteroleptic Ru(II) complexes carrying donor antenna moieties, namely, triphenylamine (TPA) or N,N′-bis(phenyl)-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD), were synthesized and applied in SDSC. These novel donor-antenna dyes revealed spectacular performances of power conversion efficiencies in the range 1.5-3.4%, as measured under AM 1.5 spectral conditions. This was attributed to highly efficient light harvesting of these novel dyes and the improved charge-transfer dynamics at TiO₂-dye and dye-hole conductor interfaces. Different low molecular weight and polymeric triphenyldiamines were synthesized and utilized as hole-transporting layers (HTL) in SDSC. Different studies showed that low molecular TPDs displayed better efficiency than polymeric counterparts due to their improved filling into the pores of nc-TiO₂ layer. Another interesting study revealed that an optimum driving force in terms of HOMO-level difference between the dye and HTL decides charge carrier generation efficiency. Recently, novel hole conductors with spiro-bifluorene-triphenylamine core for transporting holes and tetraethylene glycol side chains for binding lithium ions were synthesized and applied in SDSC. This work clearly emphasizes that Li⁺-salt is required at the TiO₂/dye interface as well as in the bulk of HTL. It was also found that the addition of about 5-20% of these Li⁺-binding hole conductors and higher Li-salt (N-lithiotrifluoromethane sulfonamide) concentrations improved the SDSC performance. An improvement of about 120% in the solar cell efficiency as compared to the reference cells was achieved with an optimum composition of Li⁺-binding hole conductor and Li-salt.     

Nanowire‐Based Three‐Dimensional Transparent Conducting Oxide Electrodes for Extremely Fast Charge Collection

A 3D transparent conducting oxide (3D‐TCO) has been fabricated by growing Sn‐doped indium oxide (ITO) nanowire arrays on glass substrates via a vapor transport method. The 3D TCO charge‐collection properties have been compared to those of conventional two‐dimensional TCO (2D‐TCO) thin films. For use as a photoelectrode in dye‐sensitized solar cells, ITO‐TiO₂ core‐shell nanowire arrays were prepared by depositing a 45 nm‐thick mesoporous TiO₂ shell layer consisting of ～6 nm anatase nanoparticles using TiCl₄ treatments. Dye‐sensitized solar cells fabricated using these ITO‐TiO₂ core‐shell nanowire arrays show extremely fast charge collection owing to the shorter electron paths across the 45 nm‐thick TiO₂ shell compared to the 2D TCO. Interestingly, the charge‐collection time does not increase with the overall electrode thickness, which is counterintuitive to conventional diffusion models. This result implies that, in principle, maximum light harvesting can be achieved without hindering the charge collection. The proposed new 3D TCO should also be attractive for other photovoltaic applications where the active layer thickness is limited by poor charge collection.     

Triblock‐Terpolymer‐Directed Self‐Assembly of Mesoporous TiO2: High‐Performance Photoanodes for Solid‐State Dye‐Sensitized Solar Cells

A new self‐assembly platform for the fast and straightforward synthesis of bicontinuous, mesoporous TiO₂ films is presented, based on the triblock terpolymer poly(isoprene ‐ b ‐ styrene ‐ b ‐ ethylene oxide). This new materials route allows the co‐assembly of the metal oxide as a fully interconnected minority phase, which results in a highly porous photoanode with strong advantages over the state‐of‐the‐art nanoparticle‐based photoanodes employed in solid‐state dye‐sensitized solar cells. Devices fabricated through this triblock terpolymer route exhibit a high availability of sub‐bandgap states distributed in a narrow and low enough energy band, which maximizes photoinduced charge generation from a state‐of‐the‐art organic dye, C220. As a consequence, the co‐assembled mesoporous metal oxide system outperformed the conventional nanoparticle‐based electrodes fabricated and tested under the same conditions, exhibiting solar power‐conversion efficiencies of over 5%.     

Synthesis, characterization and l-lactide polymerization behavior of bis(amidinate) rare earth metal amide complexes

A family of neutral and solvent-free bis(amidinate) rare earth metal amide complexes with a general formula [RC(N-2,6-Me₂C₆H₃)₂]₂LnN(SiMe₃)₂ (R = phenyl (Ph), Ln = Y (1), Nd (2); R = cyclohexyl (Cy), Ln = Y (3), Nd (4)) were synthesized in high yields by one-pot salt metathesis reaction of anhydrous LnCl₃, amidinate lithium salt [RC(N-2,6-Me₂C₆H₃)₂]Li, and NaN(SiMe₃)₂ in THF at room temperature. Single crystal structural determination of complexes 1, 2 and 4 revealed that the central metal adopts distorted pyramidal geometry. In the presence of 1 equivalent of ⁱPr-OH, all these complexes were active for l-lactide polymerization in toluene at 70 °C to give high molecular weight (M_n > 10⁴) polymers.     

CoS NWs/Au Hybridized Networks as Efficient Counter Electrodes for Flexible Sensitized Solar Cells

A newly designed counter electrode (CE) composed of a hybridized structure of Au networks and cobalt sulfide (CoS) nanowire (NW) arrays is presented for flexible dye‐sensitized solar cells (DSSCs) and quantum dot‐sensitized solar cells (QDSSCs). The sheet resistance of the Au networks electrode is ≈10 Ω sq^?1 with a transmittance up to 90%. The CoS NWs/Au hybridized networks show excellent electrocatalytic activity and lower charge transfer resistance toward the reduction of both S_x^2? ions and I₃^? ions. The hybridized electrode exhibits remarkable mechanical strength and no obvious changes in morphology and sheet resistance even after 500 bending cycles; 3.13% and 4.73% efficiency are obtained by utilizing CoS/Au hybridized networks as CEs in TiO₂ nanotube array (TNAR) based DSSCs and QDSSCs. This work provides a novel approach to fabricate flexible, transparent, conductive, and catalytically active electrodes for QDSSCs and DSSCs and pomotes the development of transparent percolation conductive films for photovoltaics.     

A batch decolorization and kinetic study of Reactive Black 5 by a bacterial strain Enterobacter sp. GY-1

An Enterobacter strain (GY-1) with high activity of decolorization of Reactive Black 5 (RB 5) was isolated from textile wastewater treating sludge. The kinetic characteristics of dye decolorization by the strain GY-1 were determined quantitatively using the diazo dye, RB 5. Effects of different operation parameters (inoculum size, pH, temperature and salinity) and various electron donors on decolorization of the azo dye by GY-1 were systematically investigated to reveal the primary factors that determine the performance of the azo dye decolorization. The decolorization of RB 5 was attributed to extracellular enzymes. A kinetic model was established giving the dependence of decolorization rate on cell mass concentration (first order). Decolorization rate increased with increasing temperature from 20 to 35 °C, which can be predicted by Arrhenius equation with the activation energy (E_a) of 8.50 kcal mol⁻¹ and the frequency factor (A₀) of 6.28 × 10⁷ mg l g MLSS⁻¹ h⁻¹. Michaelis-Menten kinetics and Eadie-Hofstee plot were used to determine V_max, 1.05 mg l⁻¹ h⁻¹ and K_m, 24.06 mg l⁻¹.     

Bio-kinetic analysis on treatment of textile dye wastewater using anaerobic batch reactor

An anaerobic digestion technique was applied to textile dye wastewater aiming at the colour and COD removal. Pet bottles of 5 L capacity were used as reactor which contains methanogenic sludge of half a liter capacity which was used for the treatment of combined synthetic textile dye and starch wastewater at different mixing ratios of 20:80, 30:70, 40:60, 50:50 and 60:40 with initial COD concentrations as 3520, 3440, 3360, 3264 and 3144 mg L⁻¹, respectively. The reactor was maintained at room temperature (30 ± 3 °C) with initial pH of 7. The maximum COD and colour removal were 81.0% and 87.3% at an optimum mixing ratio of 30:70 of textile dye and starch wastewaters. Both Monod’s and Haldane’s models were adopted in this study. The kinetic constants of cell growth under Haldane’s model were satisfactory when compared to Monod’s model. The kinetic constants obtained by Haldane’s model were found to be in the range of μ_max = 0.037-0.146 h⁻¹, K_s = 651.04-1372.88 mg L⁻¹ and K_i = 5681.81-18727.59 mg L⁻¹.     

New photosensitizers based upon [Fe(L)2(CN)2] and [FeL3], where L is substituted 2,2′-bipyridine

Ultrafast electron transfer in the dye sensitized solar cell (DSSC) has made it possible to use iron(II) polypyridyl complexes as photosensitizers [J. Am. Chem. Soc. 120 (1998) 843]. Although ruthenium(II) polypyridyl complexes comprise an extensively studied and widely utilized photochemical system, comparatively little is known about the photoproperties of their iron analogues. The syntheses and solution properties of the complexes [Fe^II(L)₂(CN)₂] and [Fe^IIL₃] for a series of L, where L is a 2,2′-bipyridine derivative, are presented here. We compare the solvatochromism of [Fe^II(4,4′-dicarboxylic acid-2,2′-bipyridine)₂(CN)₂] to [Fe^II(4,4′-dimethyl-2,2′-bipyridine)₂(CN)₂] and discuss general trends in the electrochemistry and absorption properties within the series. The solvatochromism of these complexes is discussed in terms of their use in a dye sensitized TiO₂ solar cell.     

Influence of NaCl and Na2SO4 on the kinetics and dye decolorization ability of crude laccase from Ganoderma lucidum

In a solid state medium using yellow passion fruit waste as substrate, the basidiomycete Ganoderma lucidum produced a laccase as the main ligninolytic enzyme. This crude enzyme presented Michaelian behavior with both substrates tested, namely 3-ethylbenzthiazoline-6-sulphonic acid (ABTS) and the anthraquinone dye remazol brilliant blue R (RBBR). The K_M’s for these substrates were, respectively, 0.232 × 10⁻³ and 0.602 × 10⁻³ M. The actions of NaCl and Na₂SO₄, two important salts usually found in textile wastewaters, were investigated. The enzyme was inhibited by NaCl, but not by Na₂SO₄. Inhibition by NaCl was of the mixed type with two different inhibition constants. The enzyme was able to completely decolorize RBBR in the presence of 1.0 M Na₂SO₄ and 50% decolorization was found in the presence of 0.1 M NaCl. Such properties certainly make the enzyme a good agent for textile dye effluent treatment considering the fact that wastewaters of this industry usually contain high concentrations of NaCl and Na₂SO₄.     

Heterobimetallic M/Zn (M = Cu, Ni) complexes with open-chain N- and N,O-ligands: Template synthesis from metal powders and supramolecular crystal structures

A series of new heterometallic Cu^IIZn^II and Ni^IIZn^II complexes with N- and N,O open-chain multidentate ligands (L¹ = 4,6,6-trimethyl-1,9-diamino-3,7-diazanon-3-ene; L² = 3,7-bis(2-aminoethyl)-1,3,5,7-tetraazabicyclo[3.3.1]nonane; L³ = 1,15-dihydroxy-7,9,9-trimethyl-3,6,10,13-tetraazapentadec-6-ene and L⁴ = 1-hydroxy-9-oxy-4,6,6-trimethyl-3,7-diazanon-3-ene) have been prepared through the “direct template synthesis” approach, which is a combination of classical template reactions of amines with acetone/formaldehyde and the “direct synthesis” method based on using elemental metals as starting materials. There is a significant decrease in the reaction time when the “direct synthesis” method is used compared to the conventional template condensation methods. X-ray crystallographic analyses of the complexes with the general formula M(L)ZnX₄ and [CuL⁴ZnCl₃]₂ (M = Cu²⁺, Ni²⁺; L = L¹-L³; X = Cl⁻, NCS⁻) reveal the presence of long intermolecular distance interactions, such as semi-coordination, S?S and H-bonding, in their crystal organization.     

Evaluation of passive solar heating and alternative flow regimes on nitrate removal in denitrification beds

Denitrification beds are a simple and relatively inexpensive technology for removing nitrate from point source discharges. To date, operational beds have used wood media as the carbon source, as it provides a sustained nitrate removal rate (2-10 g N m⁻³ of media d⁻¹) while maintaining permeability. In pilot-scale (2.9 m⁻³) denitrification beds receiving municipal wastewater effluent dosed with KNO₃, we looked at improving nitrate removal by using alternative carbon media (maize cobs) and increasing bed temperature through passive solar heating. The influence of flow regime (horizontal-point, horizontal-diffuse, downflow and upflow) on short-circuit flow was also investigated.The long-term nitrate removal rate (21.8 g N m⁻³ d⁻¹) of the maize cob beds over the 15-month period of the trial was 2-11-fold higher than sustained removal rates reported by other researchers for wood-based beds. While passive solar heating raised the mean bed temperature by 3.4 °C, it did not cause a measurable increase in the nitrate removal rate due to the variability in the removal rate exceeding the expected increase due to temperature.Horizontal flow had more short-circuiting than vertical flow. Short-circuiting in the horizontal flow was attributed to flow being concentrated near the top surface due to the buoyancy effect of warmer water. Greater short-circuiting in the solar heated horizontal and upflow beds than in the corresponding unheated beds was attributed to the buoyancy effect being more pronounced in the solar heated beds.Overall, downflow was deemed the most effective of the four tested flow regimes. It provided the highest increase in bed temperature due to solar heating, had the highest nitrate removal rate in the latter part of the trial and had more plug-flow characteristics. While passive solar heating raised bed temperature, we were unable to demonstrate a significant difference (at 95% CL) in nitrate removal rate between the unheated and solar heated beds because of the high variability in nitrate removal rate and the increase in short-circuiting in the solar heated horizontal and upflow beds.     

Effect of substituent dtp to optical properties of heterobimetallic M/Ag/S nest-shaped clusters (M = Mo, W)

Clusters [MoS₄Ag₃(PPh₃)₃{S₂P(OPrⁱ)₂}] (1), [WS₄Ag₃(PPh₃)₃{S₂P(OPrⁱ)₂}] (2) and [WOS₃Ag₃(PPh₃)₃{S₂P(OPrⁱ)₂}] (3) were synthesized by the reaction of (NH₄)₂MoS₄/(NH₄)₂WS₄, (NH₄)₂WOS₃ with Ag[S₂P(OPrⁱ)₂]. Their structures have been characterized by X-ray diffraction. The clusters consist of a distorted tetrahedral MS₄ (or MOS₃) (M = Mo, W) with three Ag atoms and three sulfur atom bridges (Fig. 1), and resemble roughly that of cubane-like clusters. The nonlinear optical (NLO) properties were studied with an 8 ns pulsed laser at 532 nm. Its optical response to the incident light exhibits good optical absorptive and refractive effects, with α₂ = 1.56 × 10⁻¹⁰ m W⁻¹, n₂ = 3.87 × 10⁻¹⁷ m² W⁻¹ for cluster 1; α₂ = 1.33 × 10⁻¹⁰ m W⁻¹, n₂ = 6.52 × 10⁻¹⁷ m² W⁻¹for cluster 2; and α₂ = 2.54 × 10⁻¹⁰ m W⁻¹, n₂ = 4.07 × 10⁻¹⁷ m² W⁻¹ for cluster 3 for a 1.56 × 10⁻⁴ mol dm⁻³ CH₂Cl₂ solution.     

Electrochemical immunosensor for α-fetoprotein detection using ferroferric oxide and horseradish peroxidase as signal amplification labels

An electrochemical immunosensor for quantitative detection of α-fetoprotein (AFP) in human serum was developed using graphene sheets (GS) and thionine (TH) as electrode materials and mesoporous silica nanoparticles (MSNs) loaded with ferroferric oxide (Fe₃O₄) nanoparticles and horseradish peroxidase (HRP) as labels for signal amplification. In this study, the compound of GS and TH (GS–TH) was used as a substrate for promoting electron transfer and immobilization of primary antibody of AFP (Ab₁). MSNs were used as a carrier for immobilization of secondary antibody of AFP (Ab₂), Fe₃O₄, and HRP. The synergistic effect occurred between Fe₃O₄ and HRP and greatly improved the sensitivity of the immunosensor. This method could detect AFP over a wide concentration range from 0.01 to 25 ng ml⁻¹ with a detection limit of 4 pg ml⁻¹. This strategy may find wide potential application in clinical analysis or detection of other tumor markers.     

[Ru(phen)2(dppz)] as an efficient optical probe for staining nuclear components

The ‘molecular light switch’ complexes [Ru(bpy)₂(dppz)]²⁺ (1) and [Ru(phen)₂(dppz)]²⁺ (2), where bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline and dppz = dipyrido[3,2-a:2′,3′-c]phenazine, have been explored as probes for diagnosing and staining nuclear components. The phen complex acts as a better staining agent for nonviable cells than for viable cells and exhibits a staining efficiency in tail region of comet more specific and stronger than the already known dye Hoechst 33258.