Visible luminescence spectroscopy of free-base and zinc phthalocyanines isolated in cryogenic matrices

The absorption, emission and excitation spectra of ZnPc and H(2)Pc trapped in Ne, N(2), Ar, Kr and Xe matrices have been recorded in the region of the Q states. A comparison of the matrix fluorescence spectra with Raman spectra recorded in KBr pellets reveals very strong similarities. This is entirely consistent with the selection rules and points to the occurrence of only fundamental vibrational transitions in the emission spectra. Based on this behaviour, the vibronic modes in emission have been assigned using results obtained recently on the ground state with large basis-set DFT calculations [Murray et al. PCCP, 12, 10406 (2010)]. Furthermore, the very strong mirror symmetry between excitation and emission has allowed these assignments to be extended to the excitation (absorption) bands. While this approach works well for ZnPc, coupling between the band origin of the S(2)(Q(Y)) state and vibrationally excited levels of S(1)(Q(X)), limits the range of its application in H(2)Pc. The Q(X)/Q(Y) state coupling is analysed from data obtained from site-selective excitation spectra, revealing pronounced matrix and site effects. From this analysis, the splitting of the Q(X) and Q(Y) states has been determined more accurately than in any previous attempts.     

Synthesis,characterization and fluorescence behavior of new fluorescent probe phthalocyanines bearing coumarin substituents

In this study, we report a new ligand, 6-hexyloxy-3-[p-(3′,4′-dicyanophenoxy)phenyl]coumarin, and its fluorescent tetrasubstituted phthalocyanines {M[Pc(OBzCou)₄], M = 2H, Zn(II), Co(II); Bz: Benzene}. The effect of the coumarin derivative on the intensity of the fluorescence spectra of the metal-free (H₂Pc) and zinc phthalocyanine (ZnPc) derivatives was investigated. The change of the emission properties of both the coumarin moieties and the phthalocyanine core in the presence of the metal ion and the ring-opening reaction of the coumarin were studied by means of steady-state fluorescence spectroscopy. The radiative decay of the Pcs and the treated coumarin substituents bound to the Pcs was examined. The novel chromogenic compounds were characterized by elemental analysis, ¹H NMR, ¹³C NMR, Maldi-TOF, IR and UV–Vis spectral data. The photophysical properties of the Pcs are extensively affected by their state of aggregation: in particular, dimerization and aggregation result in a remarkable modification of the absorption and emission bands and may induce significant quenching of the usually strong Pc fluorescence. The electronic spectra exhibit a band of coumarin identity together with characteristic Q and B bands of the phthalocyanine core.     

Site-specific intermolecular interaction in α-phase crystalline films of phthalocyanines studied by soft x-ray emission spectroscopy

The local electronic structures of crystalline and amorphous films of zinc phthalocyanine (ZnPc) and metal-free phthalocyanine (H(2)Pc) have been studied by soft x-ray emission spectroscopy (XES). We found a clear crystalline structure dependence of the elastic-peak shape in the resonant XES spectra. The elastic peaks of both ZnPc and H(2)Pc are found to show an asymmetric shape due to resonant inelastic x-ray scattering (RIXS) at the nitrogen sites for the α-crystalline films, but not for the amorphous films. The observed RIXS feature is ascribed to the charge transfer excitation due to the Raman-active intermolecular interaction, which dominates the excited-electron dynamics in α-crystalline phthalocyanine films.     

Supramolecular Zinc Phthalocyanine–Imidazolyl Perylenediimide Dyad and Triad: Synthesis,Complexation, and Photophysical Studies

Two new supramolecular architectures based on zinc phthalocyanine (Pc) and imidazolyl‐substituted perylenediimide (PDI), ZnPc/DImPDI/ZnPc 1 and ZnPc/ImPDI 2 , have been prepared. A strong electron‐donor, 8 , which contained eight tert‐octylphenoxy groups was synthesized to ensure high solubility, thereby reducing aggregation in solution and providing σ‐donor features while avoiding regioisomeric mixtures. Also, PDI units were functionalized with tert‐octylphenoxy groups at the bay positions, which provide solubility to avoid aggregation in solution, together with one and two imidazole moieties in the amide position, 6 and 4 , respectively, to be able to strongly coordinate with the ZnPc complex. Supramolecular complexation studies by ¹H NMR spectroscopy and ESI‐MS demonstrate a high coordinative binding constant between imidazole‐substituted 4 or 6 and 8 . The same results were confirmed by UV/Vis and fluorescence titration studies. UV/Vis titration studies revealed the formation of a 1:1 complex ZnPc/ImPDI 2 for the systems 8 and 6 and a 2:1 complex ZnPc/DImPDI/ZnPc 1 for the interaction of 8 and 4 . The binding constant in both cases was determined to be on the order of 10⁵ M ⁻¹. Femtosecond laser flash photolysis measurements provided a direct proof of the charge‐separated state within both supramolecular assemblies by observing the transient absorption band at 820 nm due to the zinc phthalocyanine radical cation. The lifetimes of charge‐separated states are (9.8±3) ns for triad 1 and (3±1) ns for dyad 2 . As far as we know, this is the first time that a radical ion pair has been detected in a supramolecular assembled ZnPc–PDI system and has obtained the longest lifetime of a charge‐separated state published for ZnPc–PDI assemblies.     

X-ray diffraction and IR spectral characteristics of zinc(II)tetra-tert-butylphthalocyanine

According to well-known procedures, alpha- and beta-crystal polymorphic modifications of zinc(II)tetra-tert-butylphthalocianine (Zn(t-Bu)4Pc) were prepared and X-ray analysis of their powders was carried out. It was found that four tert-butyl groups in Zn(t-Bu)4Pc molecule do not prevent the formation of the alpha- and beta-polymorphs. The alpha- and beta-polymorphs differ from each other mainly by a mutual arrangement of neighboring metallophthalocyenine molecules in pi-stacking. Comparison of IR spectra of the alpha- and beta-polymorphs of ZnPc and Zn(t-Bu)4Pc was carried out. It was indicated that new bands appear at 670-690, 1256 and 1362 cm(-1) in the spectrum of Zn(t-Bu)4Pc in comparison with that of ZnPc. The appearance of new band at 1256 cm(-1) is assigned to rocking C-CH(3) vibrations and the band at 1362 cm(-1) to symmetrical deformational C-H vibrations of methyl groups of the peripheral substitutes. The main spectral characteristics for identification of the polymorphic modifications of Zn(t-Bu)4Pc are listed.     

Phthalocyanine-based fluorescent chemosensor for the sensing of Zn (II) in dimethyl sulfoxide-acetonitrile

A tetra-substituted phthalocyanine based on 4-[2-(4-nitrophenoxy)ethoxy]phthalonitrile carrying nitrophenyl group for the sensing of Zn²⁺ has been prepared and characterized by elemental analysis, FT-IR, ¹H and ¹³C NMR, and MS spectral data. The sensing of Zn²⁺ is based on the fluorescence quenching of Pc. Both absorbance and fluorescence spectra of ZnPc exhibit distinct changes in visible region in response to treatment with Zn²⁺ ion in dimethyl sulfoxide. The fluorescence spectrum of the ligand showed quenching in the intensity of the signal at 688?nm for Zn²⁺. The complex composition of ZnPc was found 1:1 by means of spectrophotometric and spectrofluorimetric titration data. The spectrofluorimetric method showed good sensitivity for Zn²⁺ with linear range and detection limit of 4.0?×?10^?6–4.4?×?10^?5 and 2.4×10^?7?M, respectively.     

Effect of peripheral substitution on the electronic absorption and fluorescence spectra of metal-free and zinc phthalocyanines

The effect of substituents on the position and intensity of the electronic absorption and fluorescence spectra of phthalocyanines (Pcs) was examined for 35 Pc compounds. When electron-releasing groups are bound to four alpha-benzo positions of the Pc skeleton, the B and Q bands shift to longer wavelength. Relative to this shift, the effect of introducing the same electron-releasing groups at the other four alpha positions amounts to about 1.6-2.0. Although the effect is not always clearly seen, introduction of electron-releasing groups in the beta-benzo positions of the Pc skeleton generally shifts the Q band to shorter wavelength. The effect of electron-withdrawing groups is exactly the opposite with respect to the alpha and beta positions. These effects can be reasonably explained by considering the magnitude of the atomic orbital coefficients of the carbon atoms derived from molecular orbital (MO) calculations. In addition, the following intriguing phenomena were observed in the experiments, although not all were explained theoretically: 1) the splitting of the Q band of metal-free Pcs decreases with increasing wavelength of the Q band, 2) the ring currents of Pcs with Q bands at longer wavelength are generally smaller, and 3) the absorption coefficients of the Q band of Pc compounds with 16-electron-releasing substituents are larger than those of the corresponding tetra- and octasubstituted Pcs by several tens of percent. 4) Our PPP calculations suggested that the absorption coefficient of the Q band of Pcs with more strongly electron releasing substituents is larger. 5) The second HOMO of the Pcs with the Q band at longer wavelength has b(1u) symmetry, as opposed to the a(2u) symmetry of normal Pcs. 6) Pcs showing S1 emission maxima at wavelengths longer than about 740 nm generally have quantum yields of less than 0.1.     

Solvent effects on the photochemical and fluorescence properties of zinc phthalocyanine derivatives

The effects of solvents on the singlet oxygen, photobleaching and fluorescence quantum yields for zinc phthalocyanine (ZnPc) and its derivatives; (pyridino)zinc phthalocyanine ((py)ZnPc), zinc octaphenoxyphthalocyanine (ZnOPPc) and zinc octaestronephthalocyanine (ZnOEPc), is presented. The effects of the solvents on the ground state spectra are also discussed. The largest red shift of the Q band was observed in aromatic solvents, the highest shift being observed for 1-chloronaphthalene. Higher singlet fluorescence quantum yields were observed in THF for ZnPc and ZnOPPC. Also in the same solvent phototransformation rather than photobleaching was observed for ZnOPPc. Split Q band in the emission and excitation spectra of ZnOPPc was observed in some solvents and this is explained in terms of the lowering of symmetry following excitation.     

OCTA-ALKYL ZINC PHTHALOCYANINES: POTENTIAL PHOTOSENSITIZERS FOR USE IN THE PHOTODYNAMIC THERAPY OF CANCER

The synthesis, characterization and electronic spectra of a series of nine 1,4,8,11,15,18,22,25-octa-alkyl zinc phthalocyanines (ZnPc), potential photosensitizers for the photodynamic therapy of cancer, are described. The substituents on the phthalocyanine (Pc) macrocycle “red-shift” the absorbance maximum, in cyclohexane, of all nine members of this series to a value of 703 ± 2 nm, with a corrected fluorescence emission maximum for the octadecyl derivative of 715 nm. The solubilities and degree of aggregation of six examples in cyclohexane have been measured. The highest homologue, the octadecyl derivative, remains essentially unaggregated to a concentration of 1.5 ± 10^?4 mol dm^?3. The photostability of this Pc has been examined and the compound shown to be sensitive to photooxidation processes, which lead to its decomposition to 3,6-fcw-decylphthalimide. Known singlet oxygen quenchers inhibit the photodecomposition. In a comparative study, the octadecyl ZnPc underwent a more rapid photodecomposition than the corresponding metal-free derivative.     

Luminescence spectroscopy of matrix-isolated atomic manganese: excitation of the "forbidden" a6D(J)<-->a6S transitions

Laser-induced excitation spectra recorded for the electric-quadrupole 3d(6)4s a6D(J)<--3d(5)4s2a6S(5/2) transitions of atomic Mn, allow assignment of the red emission features, previously observed in Mn/RG (RG=Ar, Kr and Xe) matrices with resonance 3d(5)4s4pz6P(5/2)<--3d(5)4s2 a6S(5/2) excitation, to the metastable a6D(9/2) state. Narrow excitation bands recorded for the red site in the Mn/Kr system allow identification of all five spin-orbit levels (J=1/2, 3/2, 5/2, 7/2 and 9/2) in the a6D state. The coincidence of the lowest energy excitation band and the observed 585.75 nm (17,072 cm(-1)) emission band of atomic Mn in Kr matrices, yielded a definitive assignment of this emission to a transition from the J=9/2 spin-orbit level. Temperature dependent emission scans lead to the identification of the zero phonon line for the a6D(9/2)-->a6S(5/2) transition at 585.75 nm. The identified matrix-shift of +20 cm(-1) allows an assessment of the extent of the ground state stabilization in the red (secondary) site of atomic Mn isolation in solid Kr. Emission produced with direct a6D state excitation yielded both the 585.75 and 626 nm features. The former band arises for Mn atoms occupying the red site--the latter from blue site occupancy in solid Kr. The excitation linewidths recorded for these two sites differ greatly, with the blue site yielding a broad featureless profile, in contrast to the narrow, structured features of the red site. The corresponding red site a6D(J)<-->a6S(5/2) transitions in Ar and Xe matrices are broader than in Kr--a difference considered to originate from the site sizes available in these hosts and the interatomic Mn x RG potentials. The millisecond decay times recorded for the red emission bands in the Mn/RG systems are all much shorter than the 3 s value predicted for the gas phase a6D(9/2)-->a6S(5/2) transition. This enhancement allows optical pumping of the forbidden a6D(J)<-->a6S transitions with low laser powers when atomic manganese is isolated in the solid state. However all the emission decays are complex, exhibiting triple exponential decays. This behavior may be related to the dependence of the excitation linewidths on the J value, indicating removal of the J degeneracy due to weak matrix-induced, crystal field splitting.     

质子化和脱质子化对酞菁光谱的影响

系统地研究四异丙氧基酞菁的子化和脱质子化对吸收和发射光谱的影响，研究表明，三氟乙酸可对酞菁分子连续质子化，分别生成（Ｈ２Ｐｃ（Ｏ＾ｉＰｒ）４．Ｈ＾＋）＾和（Ｈ２Ｐｃ（Ｏ＾ｉＰｒ）４．２Ｈ＾＋）＾２＋，而硫酸可使酞菁形成（Ｈ２Ｐｃ（Ｏ＾ｉＰｒ）４．４Ｈ＾＋＾４＋此外，ＮａＯＨ／ＥｔＯＨ可使酞菁分子脱质子化生成（Ｐｃ（Ｏ＾ｉＰｒ）４）＾２－反应一步完成，表明分子中的两个吡咯－ＮＨ－同步酸解，质子化可使     

S1(1A1)<--S0(1A1) transition of benzo[g,h,i]perylene in supersonic jets and rare gas matrices

The study of the S1(1A1)<--S0(1A1) transition of benzo[g,h,i]perylene (BghiP, C22H12) in supersonic jets and solid rare gas matrices is reported. In the jet-cooled spectrum, the origin band position is located at 25,027.1+/-0.2 cm-1, the assignment being supported by the analysis of vibrational shifts and rotational band contours. Except for the origin band, which is weak, all bands are attributed to the fundamental excitation of nontotally symmetric b1 vibrational modes of S1. The intensity pattern is interpreted as a consequence of the weak oscillator strength of the electronic transition combined with intensity-borrowing through vibronic interaction between the S1(1A1) and S2(1B1) states. The spectra of the S1(1A1)<--S0(1A1) and S2(1B1)<--S0(1A1) transitions have also been measured for BghiP in solid neon and argon matrices. The comparison of the redshifts determined for either transition reveals that the polarizability of BghiP is larger in its S2 than in its S1 state. Bandwidths of 2.7 cm-1 measured in supersonic jets, which provide conditions relevant for astrophysics, are similar to those of most diffuse interstellar bands. The electronic transitions of BghiP are found to lie outside the ranges covered by present databases. From the comparison between experimental spectra and theoretical computations, it is concluded that the accuracy of empirical and ab initio approaches in predicting electronic energies is still not sufficient to identify astrophysically interesting candidates for spectroscopic laboratory studies.     

Effect of beta-cyclodextrin on the excited state proton transfer in 1-naphthol-2-sulfonate

The photophysical properties of 1-naphthol-2-sulfonate (1-NOH-2-S) in various solvents and in aqueous beta-cyclodextrin (CD) solution have been investigated. The fluorescence quantum yields in non-aqueous solvents are approximately 0.5, while in water the fluorescence quantum yield is 0.1. The fluorescence quantum yield doubled on the addition of beta-CD. In aqueous solution, proton transfer to water takes place efficiently leading to the formation of the anion form with its longer wavelength emission broad band at about 460 nm. Any environmental changes have been found to affect the rate of deprotonation and subsequently the band intensity at 460 nm. In non-aqueous solution the anion emission band disappears completely. Upon the addition of beta-CD to the aqueous solution of 1-NOH-2-S, the anion emission decreases with an increase in the intensity of the neutral form at 362 nm. Fluorescence measurements show 1:1 inclusion of 1-NOH-2-S in the beta-CD cavity with an association constant of 1915 M(-1) using Benesi-Heldbrand treatment. 1H NMR studies are used to confirm the inclusion and to provide information on the orientation of 1-NOH-2-S inside the cavity of beta-CD.     

Synthesis and spectroscopic properties of a novel zinc phthalocyanine with four 17-membered crown ether voids

A novel zinc phthalocyanine containing four 17-crown-5 ether voids(17C5ZnPc) has been synthesized and characterized. UV-visible absorption and fluorescence emission spectra and as-sociated photophysical parameters have been determined. In contrast to most of the crown ether substituted phthalocyanines, no cofacial dimer formation is observed in the presence of alkali metal salts. In addition to the fluorescence at 710 nm from S1, a strong upper excited state (Soret 52) emission around 424 nm has been detected for the first time in the phthalocyanine series. Fluorescence decay of S1 and S2 emission can be analyzed by mono- and biexponential fits respectively. X-ray structure analysis showed that the crown ether unit is conformationally deformed and oblate that may account for the unusual spectroscopic properties.     

Dual fluorescence of graphene oxide: a time-resolved study

The fluorescence properties of graphene oxide (GO) was studied by recording the fluorescence lifetime, fluorescence emission, and excitation spectra, as well as UV-visible and near-IR absorption spectra. For the first time, we showed that a blue band (ca. 440 nm) and a long wavelength (LW) band (ca. 700 nm) are coexistent, which can be recorded simultaneously by controlling concentration, excitation wavelength, and pH values. Two bands are closely related by the protonation or deprotonation of GO. The blue band is favored by low GO concentration, short excitation wavelength, and high pH value, while the LW band is favored by low pH and long excitation wavelength. To reveal the nature of the dual emission of GO, the fluorescence lifetimes under various conditions were also measured. The blue band contains three emitting components; one of them has a lifetime as long as 10 ns, and its emitting intensity is fairly sensitive to pH, showing the potential for applications in sensing H(+) and fluorescence lifetime imaging. Combining the results under various conditions, we conclude that the electronic transition for this component is very likely due to n-π* transition. The LW band contains two main emitting components (0.2 and 2.1 ns) that also appear in the blue band as minor contributors; the related emission is assigned to π-π* transition. In summary, GO emission is of broadband (300-1250 nm), long-lived, pH sensitive, and excitation wavelength dependent. This makes it easily tailored for versatile applications.     

Twisted Intramolecular Charge Transfer Emission of 2-(4'-N,N-dimethylaminophenyl)benzimidazole in Micelles

Spectral characteristics of 2-(4'N,N-dimethylaminophenyl)benzimidazole have been studied as a function of surfactant concentration and as a function of acid concentration in three surfactants. Dual fluorescence is observed in all the micelles. Fluorescence intensities of the local emission (B band) and twisted intramolecular charge transfer (A band, TICT) increase by an 17-30% and 38 to 64% respectively. When dissolved in micelles lifetimes of both the states also increase in the presence of micelles. The increase in the fluorescence intensities is attributed to the decrease in the non-radiative decay constant. cmc of the surfactants can be determined from the variation in the fluorescence intensity and the lifetime data. The equilibrium constants are determined for the prototropic reactions of the fluorophore in all the micelles in S0 and S1 states and the values obtained are discussed. Copyright 1999 Academic Press.     

Density functional theory study of vibronic structure of the first absorption Qx band in free-base porphin

Harmonic vibrational frequencies and vibronic intensities in the first S(0)-->S(1) (pipi( *)) absorption band of free-base porphin (H(2) P) are investigated by hybrid density functional theory (DFT) with the standard B3LYP functional. The S(0)-S(1) transition probability is calculated using time-dependent DFT with account of Franck-Condon (FC) and Herzberg-Teller (HT) contributions to the electric-dipole transition moments including displacements along all 108 vibrational modes. Two weak wide bands observed in the gas phase absorption spectra of the H(2) P molecule at 626 and 576 nm are interpreted as the 0-0 band of the X(1) A(g)-->1B(3u) transition and the 0-1 band with largest contributions from the nu(10)(a(g))=1610 cm(-1) and nu(19)(b(1g))=1600 cm(-1) modes, respectively, in agreement with previous tentative assignments. Both bands are induced by the HT mechanism, while the FC contributions are negligible. A number of fine structure bands, including combination of two vibrational quanta, are obtained and compared with available spectra from supersonic jet and Shpolskij matrices. Both absorption and fluorescence spectra are interpreted on ground of the linear coupling model and a good fulfillment of the mirror-symmetry rule.     

New fluorimetric determination of hemoglobin used as a substitute of mimietic peroxidase

Hemoglobin (Hb) could be used as a substitute of peroxidase in the catalytic oxidation of tetra-substituted amino aluminum phthalocyanine (TAA1Pc) by H2O2. We found that the fluorescence of TAA1Pc (a red-region fluorescent dye with a maximum excitation wavelength at 606 nm and a maximum emission wavelength at 673 nm) could significantly be quenched by H2O2 in the presence of Hb. The value of F0/F (where the relative fluorescence intensity of blank solution and that of the sample solution containing Hb were given by F0 and F, respectively) is linearly related to the concentration of Hb. Based on this, a novel fluorimetric method was developed for the determination of Hb in aqueous solution. Under optimal conditions, Hb could be determined in the concentration range of 5 x 10(-11) - 12 x 10(-8) mol L(-1) with a detection limit of 1.5 x10(-11) mol L(-1). The relative standard deviation of ten replicate measurements was 1.95% for solution containing 1 x10(-9 ) mol L(-1) Hb. The proposed method has been applied to the analysis of Hb in human blood and the results were in good agreement with those reported by a hospital laboratory. So this is a new, high sensitive and precise fluorescence quenching method to determine Hb.     

Structural and luminescence studies of nickel(II) and copper(II) complexes with (1R,2R)-cyclohexanediamine derived unsymmetric Schiff base

Unsymmetrical Schiff base obtained by the condensation reaction of (1R,2R)(-)cyclohexanediamine with 2-hydroxybenzaldehyde and 2-hydroxynaphthaldehyde was used as a ligand for copper(II) and nickel(II). The ligand and complexes were characterized by circular dichroism (CD), UV-VIS, fluorescence, IR and (1)H (NOE diff), NOESY and (13)C NMR (ligand) spectra. The X-ray crystal structures solved for (1R,2R)(-)chxn(salH)(naftalH) and Cu(II)(1R,2R)(-)chxn(sal)(naftal) revealed tetrahedral distortion of coordination sphere in the solid phase. The [Cu(1R,2R)(-)chxn(sal)(naftal)]·0.5EtOH·1.25H(2)O complex crystallized in the monoclinic chiral C2 space group with two molecules in the asymmetric unit as well as disordered ethanol and water molecules. For both molecules Cu(II) ions were found in square-planar environments and adopts conformation described as "semi-open armed", because of distinctly oriented arms according to cyclohexane ring defined by three torsion angles. The thin layers of the ligands, copper(II) and nickel(II) complexes were deposited on Si(111) by a spin coating method and characterized with scanning electron microscopy SEM/EDS and fluorescence spectra. The ligand layers exhibit the most intensive fluorescence band at 498 nm, which can be assigned to emission transition π* → n of Schiff base ligand. For copper(II) layers the most intensive band from intraligand transition at 550 nm was observed. The highest intensity band was registered for the layer obtained when rotation speed was 1000 rpm and time 20 s. The nickel(II) complex layers fluorescence spectra exhibit an intensive band at 564 nm. The emission maxima of the copper(II) and nickel(II) complexes are shifted towards longer wavelength in comparison to the free ligand layers. CD spectra of the complexes in solution are characteristic for tetrahedral planar distortion of the chelate ring. The (1)H NMR NOE diff were measured and the position of the nearest hydrogen atoms in the cyclohexane and aromatic rings were discussed, suggesting the tetrahedral distortion of the central ion of the coordination sphere in solution.