Synthesis, spectral properties and stability towards protolytic dissociation of the palladium(II) complexes with dipyrrolylmethene and its bis-derivatives

Palladium(II) complexes with alkylated dipyrrolylmethene (Hdpm) and its bis-derivative, biladienea, c (H₂bd), of the composition [Pd(dpm)₂] and [Pd(bd)] were synthesized and were characterized by IR, UVVIS, and NMR spectroscopy. It was shown that the nature of the solvent has almost no effect on the spectral characteristics of the complexes due to the square-planar configuration of the coordination nodes in them and, respectively, the impossibility of further coordination. From the results of the kinetic study of the complexes stability to the action of acids in the C₆H₆-CCl₃COOH mixtures it was concluded that the Pd(II) complexes are much more stable compared to the other d-metal dipyrrolylmethenates. Kinetic manifestation of polychelate effect was observed consisting in a sharp decrease in the dissociation rate of the palladium(II) complex with biladiene as compared to that with dipyrrolylmetene.     

Synthesis and photophysical properties of Cd(II) and Cu(II) complexes with decamethylated bis(dipyrrolylmethene)

Copper(II) and cadmium(II) complexes with bis(2,4,7,8,9-pentamethyldipyrrolylmethene-3-yl)-methane were synthesized. Influence of the complex-forming ion nature on the optical properties of [Cd₂L₂] and [Cu₂L₂] helicates was studied.     

Comparative studies of photophysical and photochemical properties of solketal substituted platinum(II) and zinc(II) phthalocyanine sets

A complete set of platinum(II) solketal substituted phthalocyanines has been synthesized and characterized. To evaluate their potential as Type II photosensitizers for photodynamic therapy, comparative studies of their photophysical and photochemical properties with analogous zinc(II) series have been achieved: electronic absorption, fluorescence quantum yields, lifetimes, and fluorescence quenching by benzoquinone, as well as singlet oxygen generation and photodegradation. It appears that platinum(II) phthalocyanines are worth being used as Type II photosensitizers, as they exhibit good singlet oxygen generation and appropriate photodegradation.     

Spectral and photophysical properties, photo and heat resistance of dipyrrolylmethene borofluoride complex and its hybrid material with polymethylmethacrylate

A hybrid material based on polymethylmethacrylate with immobilized borofluoride dipyrrolylmethene complex. The inclusion of the chromophore in the polymer environment is shown to result in a reduced polarization due to the weakening of the forces of intermolecular interactions. Study of spectral properties, photo and thermal stability showed that inclusion of the complex in the polymer matrix can significantly increase the photo and thermal stability and mechanical strength of the material while preserving the spectral characteristics inherent to the individual compound.     

Preparation and spectral properties of Zn(II) complexes with aryl-substituted dipyrrolylmethene and azadipyrrolylmethene

The homoleptic complexes of Zn(II) with 3,3′,5,5‘-tetraphenyl-2,2’-dipyrrolylmethene and 3,3′,5,5′-tetraphenyl-ms-aza-2,2′-dipyrrolylmethene [ZnL₂] have been prepared, and their spectral and luminescent properties have been studied. The complex with 3,3′,5,5′-tetraphenyl-2,2′-dipyrrolylmethene exhibited an intense fluorescence in the nonpolar medium, efficiently quenched in the polar solvents; thus, it can be used as a fluorescent sensor of the medium polarity.     

Spectral and photochemical properties of bifunctional compounds and their complexes

Quantum yields of the step-by-step photocyclization of diphenylamine (DPA) derivatives Ph₂N−(CH₂)n−NPh₂,n=3–6, 9, to the corresponding α,ω-di(carbazolyl)alkanes were measured. Atn>3, the presence of the second DPA group had no effect on the cyclization of the first DPA group; however, cyclization of the second DPA group was retarded after cyclization of the first DPA group. The effect was explained by quenching of the excited DPA group by the carbazole group newly formed in the semi-cyclic compound. For disubstituted propane (n=3), the mutual influence of the two groups at both stages of the reaction was found. For Part 1, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1510–1515, August, 1999.     

Synthesis, photophysical and photochemical properties of poly(oxyethylene)-substituted zinc phthalocyanines

The synthesis, photophysical and photochemical properties of the tetra- and octa-poly(oxyethylene)substituted zinc (II) phthalocyanines are reported for the first time. The new compounds have been characterized by elemental analysis, IR, 1H and 13C NMR spectroscopy, electronic spectroscopy and mass spectra. General trends are described for photodegradation, singlet oxygen, triplet state and fluorescence quantum yields, and triplet and fluorescence lifetimes of these compounds in dimethylsulfoxide (DMSO). Photophysical and photochemical properties of phthalocyanine complexes are very useful for PDT applications. The effects of the substituents on the photophysical and photochemical parameters of the zinc(II) phthalocyanines (3a, 5a and 6a) are also reported. The singlet oxygen quantum yields (Phi(Delta)), which give an indication of the potential of the complexes as photosensitizers in applications where singlet oxygen is required (Type II mechanism) ranged from 0.60 to 0.72. Thus, these complexes show potential as Type II photosensitizers. The fluorescence of the complexes was quenched by benzoquinone (BQ).     

Synthesis, photophysical and photochemical properties of substituted zinc phthalocyanines

The synthesis, photophysical and photochemical properties of the 4-({3,4,5-tris-[2-(2-ethoxyethoxy)ethyloxy]benzyl}oxy) and 4-({3,4,5-tris-[2-(2-ethoxyethoxy)ethyloxy]benzyl}thio) zinc(ii) phthalocyanines are reported for the first time. The new compounds have been characterized by elemental analysis, IR, (1)H and (13)C NMR spectroscopy, electronic spectroscopy and mass spectra. General trends are described for photodegradation, singlet oxygen, fluorescence and triplet excited state quantum yields, and triplet state and fluorescence lifetimes of these compounds in dimethylsulfoxide (DMSO). The fluorescence of the complexes was quenched by benzoquinone (BQ). The effects of the substitution on the photophysical and photochemical parameters of the zinc(II) phthalocyanines (6, 7 and 8) are also reported. Photophysical and photochemical properties of phthalocyanine complexes are very useful for PDT applications. The substituted Zn(II) phthalocyanines showed high triplet and singlet oxygen quantum yields. High singlet oxygen quantum yields are very important for Type II mechanism. Thus, these complexes show potential as Type II photosensitizers.     

Spectral and photophysical properties of mono and dinuclear Pt(II) and Pd(II) complexes: An unusual emission behaviour

Eight mononuclear complexes of the formula [M(N-N)(DHB)] and two binuclear complexes of the formula [M₂(BPY)₂(THB)] where M = Pd(II) or Pt(II), N-N = 2,2′-bipyridine (BPY), 2,2′-biquinoline (BIQ), 4,7-diphenyl-1,10-phenanthroline (DPP), 1,10-phenanthroline (PHEN); DHB = dianion of 3,4-dihydroxybenzaldehyde and THB = tetraanion of 3,3′,4,4′-tetrahydroxy benzaldazine were prepared and their electrochemical, spectral and photophysical properties were examined. These complexes were characterized by chemical analysis, IR and proton NMR spectroscopy. A detailed study on the absorption spectroscopy of these complexes was made. These complexes were found to show a low-energy solvatochromic ligand-to-ligand charge-transfer (LLCT) band. The electronic energies of these bands have been analyzed and compared with electrochemical data. Emission behaviour of the complexes of the series, [Pt(N-N)(DHB)], [Pt(N-N)(DHBA)] where DHBA is the dianion of 3,4-dihydroxybenzoic acid and [Pt₂(BPY)₂(THB)] was also investigated. These platinum complexes were found to emit from a low-energy state at low temperature and a high-energy state at room temperature. Photophysics of these complexes is also discussed.     

Synthesis, characterization and comparative studies on the photophysical and photochemical properties of metal-free and zinc(II) phthalocyanines with phenyloxyacetic acid functionalities

The synthesis and characterization of new peripherally and non-peripherally tetra-substituted metal-free and zinc(II) phthalocyanines with 2-, 3- and 4-phenyloxyacetic acid functionalities are described for the first time in this study. The new compounds have been characterized by elemental analysis, FT-IR, UV-Vis, MALDI-TOF and ¹H-NMR spectra. Photodegradation, singlet oxygen and fluorescence quantum yields, and fluorescence lifetimes of these compounds are studied in dimethylformamide (DMF). The influence of the substituent position on the phthalocyanine framework (non-peripherally or peripherally), central metal ion (metal-free or zinc) and the position of the COOH group (2-, 3- or 4-position on the phenyloxyacetic acid) on the spectroscopic, photophysical and photochemical properties have been investigated. Non-peripherally zinc(II) phthalocyanines (1b and 2b) and peripherally zinc(II) phthalocyanine (4b) gave good singlet oxygen quantum yields (Φ_Δ) (0.37, 0.39 and 0.38, respectively) which indicate the potential of the complexes as photosensitizers in applications of PDT.     

Chromenone 12-crown-4 substituted zinc phthalocyanine complexes: investigation of spectral, photophysical and photochemical properties

The synthesis of novel 6,7-[(12-crown-4)-3-[p-(3,4-dicyanophenoxy)phenyl]coumarin (1), 6,7-[(12-crown-4)-3-[p-(2,3-dicyanophenoxy)phenyl]coumarin (2), and their corresponding tetra-(chromenone 12-crown-4)-substituted zinc (II) phthalocyanine complexes (3 and 4) have been prepared. These new compounds have been characterized by elementel analysis, (1)H NMR (1 and 2), MALDI-TOF, IR and UV-Vis spectral data. The fluorescence intensity changes for 1 and 2 by addition of Na(+) or K(+) ions have been determined at 25°C in THF. Intensity of the binding Na(+)- and K(+)-complexes (1 and 2) have decreased. The effects of the chromenone crown ether on the phthalocyanine molecule concerning photophysical and photochemical properties are also investigated. Photodegredation, singlet oxygen, fluorescence quantum yields, and fluorescence lifetimes of zinc phthalocyanine complexes (3 and 4) are also examined in DMSO.     

Tuning photophysical properties with ancillary ligands in Ru(II) mono-diimine complexes

The series of complexes [XRu(CO)(L-L)(L′)₂][PF₆] (X = H, TFA, Cl; L-L = 2,2′-bipyridyl, 1,10-phenanthroline, 5-amino-1,10-phenanthroline and 4,4′-dicarboxylic-2,2′-bipyridyl; L′₂ = 2PPh₃, Ph₂PC₂H₄PPh_2, Ph₂PCHCHPPh₂) have been synthesized from the starting complex K[Ru(CO)₃(TFA)₃] (TFA = CF₃CO₂) by first reacting with the phosphine ligand, followed by reaction with the L-L and anion exchange with NaPF₆. In the case of L-L = phenanthroline and L′₂ = 2PPh₃, the neutral complex Ru(Ph₃P)(CO)(1,10-phenanthroline)(TFA)₂ is also obtained and its solid state structure is reported. Solid state structures are also reported for the cationic complexes where L-L = phenanthroline, L₂ = 2PPh₃ and X = Cl and for L-L = 2,2′-bipyridyl, L₂ = 2PPh₃ and X = H. All the complexes were characterized in solution by a combination of ¹H and ³¹P NMR, IR, mass spectrometry and elemental analyses. The purpose of the project was to synthesize a series of complexes that exhibit a range of excited-state lifetimes and that have large Stokes shifts, high quantum yields and high intrinsic polarizations associated with their metal-to-ligand charge-transfer (MLCT) emissions. To a large degree these goals have been realized in that excited-state lifetimes in the range of 100 ns to over 1 μs are observed. The lifetimes are sensitive to both solvent and the presence of oxygen. The measured quantum yields and intrinsic anisotropies are higher than for previously reported Ru(II) complexes. Interestingly, the neutral complex with one phosphine ligand shows no MLCT emission. Under the conditions of synthesis some of the initially formed complexes with X = TFA are converted to the corresponding hydrides or in the presence of chlorinated solvents to the corresponding chlorides, testifying to the lability of the TFA Ligand. The compounds show multiple reduction potentials which are chemically and electrochemically reversible in a few cases as examined by cyclic voltammetry. The relationships between the observed photophysical properties of the complexes and the nature of the ligands on the Ru(II) is discussed.     

Star-shaped electrochemiluminescent metallodendrimers with central polypyridyl Ru(II) complexes: Synthesis and their photophysical and electrochemical properties

Several dendritic bridging ligands were designed and synthesized to develop more sensitive and efficient electrochemiluminescent (ECL) polynuclear Ru(II) complexes. Various types of novel two-armed, four-armed and six-armed tris(bipyridyl)ruthenium core dendrimers were synthesized by coordinating dendritic polybipyridyl ligands with Ru(II) complexes, and the effect of the ligand and the dendritic network on the ECL characteristics were studied. Their electrochemical redox potentials, UV, photoluminescence (PL), and relative ECL intensities were also investigated in detail. The synthesized metallodendrimers exhibited strong metal-to-ligand charge transfer (MLCT) absorption at 428-451 nm and emission at 591-601 nm. Most of the newly synthesized metallodendrimers showed enhanced ECL intensities compared to the reference complex, [Ru(o-phen)₃](PF₆)₂. In particular, the ECL intensities of the six-armed heptanuclear ruthenium complexes were almost four times greater than that of [Ru(o-phen)₃]²⁺. These metallodendrimers could be utilized as efficient ECL materials and light emitting devices.     

Synthesis,photophysical and photochemical studies of water soluble cationic zinc phthalocyanine derivatives

Peripherally and non-peripherally 2-diethylaminoethanethiol tetra-substituted zinc phthalocyanine (5a and 6a) and their quaternized derivatives (5b and 6b) have been synthesized and characterized. The quaternized derivatives (5b and 6b) show excellent solubility in aqueous medium. The photophysical and photochemical properties of the 2-diethylaminoethanethiol appended zinc phthalocyanine in dimethylsulfoxide (DMSO) for the non-ionic (5a and 6a) and in both DMSO and aqueous medium (phosphate buffered saline solution PBS, pH 7.4) (in the presence and absence of cremophore EL (CEL)) for the quaternized (5b and 6b) derivatives were studied and compared with that of the peripherally octa-substituted derivatives (7a and 7b). The complexes have intense absorption in the visible/near-IR region though the quaternized forms (5b, 6b and 7b) were slightly blue shifted and highly aggregate in aqueous solution. The triplet state quantum yields (_ΦT${\Phi }_{\text{T}}$) and the triplet lifetimes (_τT${\tau }_{\text{T}}$) were found to be higher in DMSO (_ΦT${\Phi }_{\text{T}}$ values ranged from 0.57 to 0.75 while _τT${\tau }_{\text{T}}$ values ranged from 190 to 220 μs in DMSO for all complexes) compared to aqueous medium (_ΦT${\Phi }_{\text{T}}$ values ranged from 0.15 to 0.17 while _τT${\tau }_{\text{T}}$ values ranged from 20 to 70 μs in pH 7.4 buffer). Addition of cremophore EL in aqueous solution resulted in induced disaggregation leading to increased _ΦT${\Phi }_{\text{T}}$ and _τT${\tau }_{\text{T}}$.     

Asymmetric indolylmaleimide derivatives and their complexation with zinc(II)-cyclen

The spectroscopic properties of two asymmetric indolylmaleimide derivatives, 4-bromo-3-(1'H-indol-3'-yl)maleimide and 4-methyl-3-(1'H-indol-3'-yl)maleimide, are investigated. The bromo derivative was crystallized and its X-ray structure was determined. Both compounds are strongly colored while their separate components (indole and maleimide) absorb in the UV region only. To understand the ground- and excited-state behavior, the photophysical properties of the two compounds were studied in detail by steady state and time-resolved absorption and emission spectroscopy. Their solvatochromic behavior was investigated by using the Kamlet-Taft approach, which indicates some charge transfer (CT) character in the excited state. Nano- and femtosecond transient absorption spectroscopy was used for the identification and investigation of the CT state. Furthermore, the effect of the complexation with zinc(II) 1,4,7,11-tetraazacyclododecane (Zn-cyclen) on the photophysical properties of these two compounds was studied. An enhancement of the fluorescence intensity upon self-assembly (up to 90 times) and high association constants were observed, which illustrate the potential use of these compounds as luminescent sensors. DFT calculations indicate that HOMO-1 to LUMO excitation is mainly responsible for the charge transfer character and that this transition changes its character drastically when Zn-cyclen complexation occurs, thus giving it sensor properties.     

Synthesis, photophysical and electrophosphorescent properties of fluorene-based platinum(II) complexes

A series of platinum(II) complexes bearing tridentate cyclometalated C^N^N (C^N^N=6-phenyl-2,2'-bipyridine and π-extended R-C^N^N=3-[6'-(naphthalen-2'-yl)pyridin-2'-yl]isoquinoline) ligands with fluorene units have been synthesised and their photophysical properties have been studied. The fluorene units are incorporated into the cyclometalated ligands by a Suzuki coupling reaction. An increase in the π-conjugation of the cyclometalated ligands confers favourable photophysical properties compared to the 6-phenyl-2,2'-bipyridine analogues. The fluorene-based platinum(II) complexes display vibronic-structured emission bands with λ(max)=558-601 nm, and high emission quantum yields up to 0.76 in degassed dichloromethane. Their emissions are tentatively assigned to excited states with mixed (3)IL/(3)MLCT parentage (IL=intraligand, MLCT=metal-to-ligand charge transfer). The crystal structures of these platinum(II) complexes reveal extensive Pt(II)···π and/or π-π interactions. The fluorene-based platinum(II) complexes are soluble in organic solvents, have high thermal stability with decomposition temperature >350 °C, and can be thermally vacuum-sublimed or solution-processed as phosphorescent dopants for the fabrication of organic light-emitting diodes (OLEDs). A monochromic OLED with 3d as dopant (2 wt%) fabricated by vacuum deposition gave a current efficiency of 14.7 cd A(-1) and maximum brightness of 27000 cd m(-2). A high current efficiency (9.2 cd A(-1)) has been achieved in a solution-processed OLED using complex 3f (5 wt%) doped in a PVK (poly(9-vinylcarbazole)) host.     

Spectral and photochemical properties of hydroxylated 2-styrylquinoline derivatives

The spectral and photochemical properties of 2-(4-hydroxystyryl)quinoline 1 and 2-(2-hydroxystyryl)quinoline 2 have been studied. The trans-cis photoisomerization quantum yield for 1 and 2 in the neutral form is 0.2–0.5, and it is reduced by a factor of 6–7 by protonation, presumably, owing to the competitive process of hydroxyl group deprotonation in the excited state and the formation of quinoid tautomers. The quantum yield of the back cis-trans photoisomerization in the protonated form varies insignificantly. The neutral, protonated, and deprotonated forms of 1 have been used for to simulate a molecular logic gate, the half-adder with chemical inputs and absorbance as outputs.     

Copper(II) and zinc(II) complexes with terpene derivatives of ethylenediamine: unexpected ligand transformations

Crystallization of copper and zinc complexes with imino terpene derivatives of ethylenediamine causes unexpected chemical transformation of the ligand. Copper(II) chloride catalyzes the hydrolysis of the imine and also acts as a halogenating agent. Crystallization of the zinc complex in acetone is accompanied by the condensation of the ketone with the primary amino group of the ligand.     

Nickel(II) and copper(II) complexes with humic acid anions and their derivatives

Complexation of Ni(II) and Cu(II) in aqueous solutions with anions of humic acids, extracted from naturally oxidized coal, and with their hydroxymethyl derivatives is studied spectrophotometrically and potentiometrically. The complexation stoichiometry and the stability constants of the complexes are determined.