Search

At the present time, photodynamic inactivation (PDI) is receiving considerable interest for its potential as an antimicrobial therapy. The results of our study indicate that enhancement of the phototoxic effect on Pseudomonas aeruginosa can be achieved by combination of tetrasulfonated hydroxyaluminum phthalocyanine (AlPcS4) and bimetallic gold/silver nanoparticles (Au/Ag-NPs) synthesized by the cell-free filtrate of Aureobasidium pullulans. The bimetallic nanoparticles were characterized by a number of techniques including UV-vis, XPS, TEM, and SEM-EDS to be 14 ± 3 nm spherical particles coated with proteins. The effect of diode lasers with the peak-power wavelength ʎ = 650 nm (output power of 10 and 40 mW; radiation intensity of 26 and 105 mW/cm2) in combination with the AlPcS4 and the bimetallic nanoparticles mixture on the viability of P. aeruginosa rods was shown. Particularly high efficiency of killing bacterial cells was obtained for the light intensity of 105 mW/cm2, after 20, 30, and 40 min of irradiation corresponding to 126, 189, and 252 J/cm2 energy fluences. For AlPcS4+Au/Ag-NPs treatment, the viable count reduction were equal to 99.90, 99.96, and 99.975%, respectively. These results were significantly better than those accomplished for irradiated separated assays of AlPcS4 and Au/Ag-NPs.

Aggregation of soluble sulfonated phthalocyanines (Pcs) containing di- and trivalent central atoms in binary water-alcohol solvents has been studied. The equilibrium constants of dimerization in solutions of Pcs with divalent central atoms (Zn, Cu) were found dependent on the electrical permittivity of the solvent and on the degree of sulfonation (i.e., on the charge on the phthalocyanine anions). Our results show that in Pcs with the trivalent central atom (Al(OH)) the dimerization occurs preferentially by formation of oxygen bridges or hydrogen bonds. Disulfonated aluminum phthalocyanine anions dissolved in water-rich binary solvents seem to form both π -stacked dimers and chemical dimers, due to a decrease in the Coulombic repulsive energy. The experiments reported in the paper indicate that the aggregation of soluble phthalocyanines can be controlled by the choice of a suitable electric permittivity of the solvent.

Fluorescence of nonlinear optical organic single crystal of 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) excited by a nonabsorbed light pulses from Q-switched Nd:YAG laser λ = 1064 nm as well as absorbed λ = 532 nm light is reported. Two mechanisms of two-photon excited fluorescence are considered: (i) direct two-photon excited fluorescence and (ii) single-photon excitation due to reabsorption of light generated in process of second harmonic generation (SHG) by the crystal due to its nonlinear optical properties. Strong anisotropy of fluorescence that has been observed is linked with uniaxial molecular alignment. Fluorescence decay profile shows two- exponential decay with lifetimes of emitting species of 3.7 and 5.6 ns at 293 K. The excitation and fluorescence spectra of the DCNP single crystal have been measured at 294 K and in function of temperature down to 77.4 K. The strong bathochromic shift of fluorescence spectrum in crystal with respect to fluorescence of DCNP molecule in solution is observed and interpreted with possible formation of molecular aggregates.

Dimerization of sulfonated phthalocyanines of divalent metals (Zn, Cu, and Co) in binary water-alcohol solutions was studied by spectroscopic techniques. The dimerization manifests itself in changes in the absorption spectra and in a decrease of fluorescence intensity. The equilibrium constants of dimerization depend on the electric permittivity of the solvent and on degree of sulfonation. The process can be semi-qualitatively described by a simple model taking into account solvation and electrostatic interactions between phthalocyanine anions. The effect of electric permittivity has not been observed in sulfonated Al and Si phthalocyanines. Experimentally determined fluorescence quantum yields in alcoholic solutions range between 0.74 and 0.015.

Luminescence and amplified spontaneous emission (ASE) phenomenon of 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) dissolved in a polymethyl methacrylate (PMMA) matrix have been studied. We analyzed luminescence from thin films of DCNP–PMMA excited by the neodymium doped yttrium aluminum garnet (Nd:YAG) nanosecond pulsed laser doubled and tripled in frequency. We report on ASE in function of different excitation pulse energy densities (ASE threshold was estimated to be 10 and 13 mJ/cm2 for pumping beams wavelengths of 532 and 355 nm, respectively). We observed the photo-degradation process of a dye and performed exponential gain coefficient measurements (up to 10 cm−1) in the system.

Energy transfer between CdSe quantum dots (QDs) as donors and Zn phthalocyanine (Zn-Pc) molecules as acceptors was studied using steady-state photoluminescence and time-correlated single photon counting techniques. With the latter technique it is evaluated that the lifetime of Zn-Pc emission increases from 4 ns to ca. 30 ns on 460 nm excitation in the presence of the QDs. The concomitant decrease in the lifetime of the QDs emission (from 23.5 to 18.4 ns) indicates that the excitation of Zn-Pc occurs not only through reabsorption but also through fluorescence resonance energy transfer.

Sodium salts of sulfonated hydroxyaluminum phthalocyanines [Al(OH)Pc(SO3Na)i] containing various numbers of sulfonate groups (i = 1–4), were studied by spectroscopic techniques. The lifetimes of the singlet states were found to range between 5 and 8 ns, experimentally determined fluorescence quantum yields ranging between 0.45 and 0.74. Both parameters depend on the number of sulfonate groups, the singlet lifetime depending additionally on concentration. The triplet lifetime was indirectly estimated for aqueous solutions of Al(OH)Pc(SO3Na)3 to amount to ca. 0.6 μs. The decay time of singlet oxygen in the same system was also found to be close to 0.6 μs. The molecules were found to dimerize in acidic and neutral solutions, the second order rate constants of the dimerization being of the order of 10 mol−1 dm3 s−1, and the equilibrium constants of the order of 104. The experiments were supplemented with quantum chemical calculations allowing us to assign electronic transitions in monomers and dimers.

The morphology of thin films of N,N′-dimethyl-3,4,9,10-perylenetetracarboxylic acid diimide (DMe-PTCDI), vacuum deposited onto quartz substrates, kept at various temperatures (Ts) between 300 and 450 K, was investigated by the Atomic Force Microscopy. The samples were polycrystalline, with no appreciable amount of amorphous phase. Below Ts = 330 K, the dominating forms are oval crystallites, whereas above this temperature ribbon-like crystallites prevail. Optical spectra of the films in the visible spectral region were measured and correlated with the morphology of the samples. Details of the spectra can be explained assuming the effect of two types of interactions in the films, related to the crystal structure. Photovoltage spectra of indium tin oxide/DMe-PTCDI structures were measured on samples deposited at various temperatures. The diffusion lengths of excitons, estimated from a combination of the optical and photovoltage spectra, vary with Ts. For Frenkel excitons, the exciton diffusion length amounts to (25 ± 5) nm for the films deposited at 300 K and (55 ± 5) nm for the films deposited at 370 K, whereas for charge-transfer excitons the respective values amount to (10 ± 5) nm for the films deposited at 300 K and (25 ± 5) nm for the films deposited at 370 K.

A convenient and higher yielding synthetic route to N-alkyl-bis(thiophene)phenothiazine derivatives is reported and their aggregation, electrochemical properties and polymerization are characterized. The key step in the synthesis of this group of compounds has been the Stille type coupling reaction between the N-alkyldibromophenothiazine and tin derivatives of thiophene as the best way for preparation of conjugated N-alkylphenothiazine derivatives. For this group of compounds we also present an electrochemical polymerization effect and widely adopted approach to prepare structurally ordered thin, electroconducting films by Langmuir–Blodgett technique.

Highly resolved luminescence and luminescence excitation spectra of recently synthesized LnL 3 bpy complexes, where Ln=Eu 3+ , Tb 3+ , bpy=2,2′- bipyridyne and L=phosphoroazo derivative of β-diketone: CCl 3 C(O)NP(O)(OCH 3 ) 2 , in solid state and dissolved in nematic liquid crystal 6CHBT [4-(isothiocyanatophenyl)-1-( trans -4-hexyl)cyclohexane] were measured. The photoluminescence intensity of the complexes dissolved in 6CHBT was found to exhibit a strong dependence on the electric field. The mechanism of the effect and reason of its asymmetry with respect to the sign of electric field are discussed in the paper. Luminescence decay time in various environments and experimental quantum yields of the luminescence of these compounds in CDCl 3 and CHCl 3 solutions were measured.

Highly resolved fluorescence and phosphorescence excitation and emission spectra of [5]-helicene in the Shpol'skii-type matrix n -pentane were measured at 4.2 K. New additional narrow lines have been found in emission and excitation spectra upon irradiation of [5]-helicene solutions. These lines have been attributed to dihydrobenzoperylene (DHBP)—a product of the reversible photocyclization of [5]-helicene. Energies of the singlet and triplet states of [5]-helicene, DHBP and benzoperylene (BP) (a product of a subsequent dehydrogenation of DHBP) were compared with the results of quantum-chemical calculations. Fundamental frequencies of [5]-helicene and DHBP in the states S 0 and S 1 were determined from the vibrational analysis of the excitation and emission spectra. Vibrational frequencies detected in the emission and excitation spectra of [5]-helicene, DHBP and BP as well as data for [5]-helicene and BP obtained from IR and Raman spectra are in good agreement with the calculated vibrational frequencies.

Fluorescence excitation and emission spectra of perylene in n-alkane Shpol'skii matrixes have been studied at liquid helium temperature. The presence of a dominant Shpol'skii site has been detected in all matrixes and attributed to perylene molecules substitutionally entering the host lattice. The character of the highest-energy site observed in all matrixes was found to be strongly dependent on the nature of solvent. Three matrixes were selected for a comparative study: n-hexane, forming a “good” matrix, and n-decane and n-undecane, forming “poor” matrixes. A vibrational analysis of all Shpol'skii sites was performed, and an additional low-frequency out-of-plane vibration at ca. 190 cm-1 was observed for the highest energy site in n-decane and n-undecane matrixes in highly resolved two-dimensional spectra. Vibrational frequencies detected in “conventional” emission and excitation spectra and in two-dimensional spectra, as well as data from infrared and Raman spectra, are in a good agreement with recalcu...

We present a combined quantum mechanics/molecular mechanics study of the Shpol’skii system perylene/n-hexane. The system was modeled utilizing a customized pcff-derived force field optimized with a balanced set of optimization criteria based on geometry, vibrational modes, and the energies and forces in an ensemble of molecular geometries. Spectral shifts were calculated perturbatively using the method of Shalev et al. [J. Chem. Phys. 95, 3147 (1991)]. The calculated shifts are within the experimental uncertainty of the observed 0–0 lines and allow an unambiguous assignment of the three most prominent sites. The proposed assignment differs from that of a previous study.

The solvatochromic effect was studied in the family of benzimidazole-based zwitterionic betaine dye molecules. The ground-state dipole moments of the molecules were determined from dielectric measurements; depending on the substituents, they ranged from ca. 6 to over 13 Debye units. A pronounced shift of the lowest-lying absorption band was found depending on the polarity of solvents: the betaine dyes substituted with the dimethylamine group in the terminal phenyl ring exhibit a bathochromic shift whereas the dye unsubstituted or substituted with the nitro group exhibit a hypsochromic shift. The comparison of the experimental results with the quantum-chemical calculations seems to indicate that the reason for this difference rests in enhanced probability of specific interactions in the former betaines (possible formation of hydrogen bond to the imidazole nitrogen).

We report on results of measurements of the solvatochromic effect in two benzimidazole-based betaines (hereafter referred to as IB1 and IB2). The solvatochromic shifts exceed 2000 cm−1 in both molecules; however, the directions of the shift were found opposite in spite of similar chemical structures of the molecules under study. The ground-state dipole moments in both betaines exceed 13 Debye units, whereas the excited-state moments, calculated from the solvatochromic shift, differ markedly amounting to ca. 3 D in IB1 and 18 D in IB2. Quantum-chemical calculations indicate that betaines enjoy some freedom of orientation of their fragments which may influence the energies and intensities of the electronic transitions. The second-order hyperpolarizabilities, estimated from the measurements amount to ca. 20×10−40 m4/V (4.8×10−30 esu) for IB1 and 55×10−40 m4/V (13.8×10−30 esu) for IB2.

The ground- and excited-state dipole moments of a zwitterionic benzimidazole-based pyridinium betaine dye [2,4,6-triphenylpyridinium-1-(1H-benzimidazol-2-ide), hereafter referred to as IB1] were determined. The ground-state dipole moment, calculated from measurements of the static electric permittivity of IB1 in 1,4-dioxane, exceeds 13 D units. The charge distribution in the molecule changes significantly upon excitation: the excited-state dipole moment, calculated from the solvatochromic shift of the low-energy UV−vis absorption band, is equal to ca. 3 D. The experimental results are supported by quantum-chemical calculations, which indicate that both the molecular geometry and positions of the energy levels are crucially influenced by solute−solvent interactions. The vectorial part of the second-order hyperpolarizability of IB1 molecules was estimated from the experimental data employing the two-state model: its off-resonance value amounts to ca. −15 × 10-40 m4/V (−3.6 × 10-30 esu).

Results of measurements of the solvent-dependent shift of the low-energy absorption band solvatochromic effect in a benzimidazole-based betaine are reported in the paper. Measurements of absorption spectra in several solvents of different polarities were performed. The solvatochromic shift of the low-lying absorption band was found to exceed 3000 cm -1 ; the results obtained were then employed to calculate the groundand excited-state dipole moment of the molecule. The spectroscopic measurements were supplemented by measurements of the ground-state dipole moment. A remarkable change in the charge distribution was found to occur upon the electronic excitation: both the experimental results and the calculations indicate that the ground-state dipole moment is close to 13 D, whereas in the excited state it amounts to ca. 3 D. The second-order hyperpolarizability of the molecule was calculated from the measurements; its off-resonance value amounts to ca. 20 x 10 -40 m4 /V (4.8 x 10 -30 esu), depending on the solvent used. PACS numbers: 33.20.—t, 42.65.An, 42.70.Jk, 78.40.-q

Organic nanocrystals (ONCs) similarly to inorganic ones show interesting size effects. It has been already observed that their luminescence properties can be changed in terms of enhanced luminescence and spectral shift of fluorescence bands as compared to bulk materials. Usually these effects are observed for much larger size of nanoparticles from 50 nm up to 1000 nm. Noncentrosymmetric and fluorescent organic crystals are rare but particularly interesting as they exhibit both nonlinear optical properties like Second Harmonic Generation (SHG) and fluorescence. Such ONC's could serve as fluorescent and SHG probes for bio-imaging purposes simultaneously. This could be beneficial for situation in which the dynamics of ordering of biological systems has to be studied. Here, we report on 3-(1,1-dicyanoethenyl)-1-phenyl-4,5- dihydro-1H-pyrazole (DCNP) compound which forms nanocrystals, exhibits large shifts of fluorescence maximum with size and strong SHG signals. When embedded in polymeric or biopolymeric matrix DNA-CTMA shows efficient amplified spontaneous emission. The unique properties of this compound in its various forms from molecules, ONC's to macroscopic single crystals are studied and discussed.

Dispersion of the vectorial part of DCNP molecular second order hyperpolarizability βCT(-2ω;ω,ω) was calculated from solatochromic method supplemented with a separately measured ground state dipole moment of DCNP and from quantum-mechanical calculations basing on two-level model. Photoconductivity and pyroelectric properties of DCNP combined with large electrooptic coefficient observed in this material may be useful in formation of transient gratings.

Results of calorimetric studies of C70 fullerene obtained from toluene-containing solutions are described. The measurements allowed us to identify a phase transition occurring at 195 K in a 1:1 C70-toluene adduct. The transition is probably of the second order, the corresponding entropy being close to the value of R ln 2 expected of an order-disorder transition. The results presented confirm earlier literature reports concerning an irreversible process occurring at 430 K, and associated with the decomposition of the adduct.

Results of calorimetric studies of C70 fullerene are reported. A phase transition at 195 K was found in pristine C70 samples crystallized from toluene-containing solutions, the material being identified as a 1:1 C70-toluene adduct. Heating pristine samples over 430 K results in an irreversible decomposition of the adduct. Measurements of the specific heat of thermally treated C70 samples allow for identification of three phase transitions between 274 and 337 K: in addition to transitions at 274 and 337 K described in the literature, we found a transition at 307 K. The order-disorder transition at 274 K is associated with rotation of C70 molecules around their long axes and is characterized by an insignificant hysteresis between heating and cooling runs. We determined the transition entropy to amount approximately to R ln 4. The other transitions occurring at 307 and 337 K and exhibiting important hystereses are probably due to release of remaining rotational freedom associated with a re-arrangement of the crystal lattice between hexagonal and regular packings.

Two-dimensional luminescence and luminescence excitation spectra of C[sub 60] and C[sub 70] fullerenes were recorded in glassy toluene solutions, polycrystalline toluene, and benzene matrices and in a Shpolskii type n-hexane matrix at 77 K. The energies of the lowest excited singlet states of C[sub 60] and C[sub 70] as well as of the lowest triplet state of C[sub 70] were determined experimentally and compared with respective values calculated using a modified INDO method. The calculated S[sub 1]-S[sub 2] energy difference in C[sub 70] was found to be quite large and the S[sub 1]-T[sub 1] splitting in both C[sub 60] and C[sub 70] very small. The spectra exhibit a pronounced dependence on the nature of the solvent used. 25 refs., 9 figs., 1 tab.

Fluorescence, phosphorescence and excitation spectra, of [4]-, [5]-, [6]-,and [7]-helicenes in policrystalline matrices were obtained at 4.2 K. Highly-resolved electronic spectra were observed for [4]-, [5]-,and [6]-helicene whereas for [7]-helicene only broad bands were monitored in emission and excitation spectra. Irradiation of [5]-helicene at 4. 2 K leads to its photocy- clization to dihydrobenzoperylene. The observed concentration effects in [4]-, and [6]-helicene as well as influence of the crystallinity of the medium on the nuorescence-to-phosphorescence intensity ratios are explained assuming the presence of the fluorescent but not phosphorescent preaggregates. The vibronic structures of the site-selected [4]-, and [6]-helicene phosphorescence excitation spectra point to site-dependent distortions of the helicene molecules. Calculations of electronic transitions helicene molecules were performed with the modified Warshel-Karplus method.

Highly resolved fluorescence, phosphorescence and phosphorescence excitation spectra of tetrahelicene (THL) and hexahelicene (HHL) in polycrystalline matrices were obtained at liquid helium temperature. The observed concentration effects as well as the influence of the crystallinity of the medium on the fluorescence-to-phosphorescence intensity ratios are explained assuming the presence of fluorescent but not phosphorescent preaggregates and aggregates of the helicenes in crystalline matrices. The vibronic structures of the site-selected THL phosphorescence excitation spectra point to site-dependent distortions of the THL molecules. Calculations of electronic transitions of the HHL molecule were performed with the modified Warshel-Karplus method. The activity of out-of-plane skeletal modes in S 1 ↔S 0 and T 1 →S 0 HHL spectra correlates with the calculated HHL helix pitch changes in S 1 and T 1 states, respectively.

The total luminescence spectroscopy (TLS) method was used to study electronic spectra of aromatic hydrocarbons in polycrystalline and glassy matrices. Characteristic patterns of zero-phonon lines with their phonon wings, single-site spectra, multiplet spectra, and strongly inhomogeneously broadened spectra are discussed in terms of discretely and continuously distributed electronic energy levels of guest molecules. An overview of different types of excitation-emission dependences is presented.

In this paper, we present results of detailed studies on amplified spontaneous emission (ASE) and lasing achieved in a double-layer system consisted of a biopolymer based matrix loaded with 3-(1,1-dicyanoethenyl1)-1phenyl-4,5dihydro-1H-pyrazole organic nonlinear optical dye and photochromic polymer. The laser action was achieved via distributed feedback configuration with third order of Bragg scattering on surface relief grating generated in photochromic polymer. To excite the luminescence, we have used 6 ns pulses of Nd:YAG laser at 532 nm. The ASE and lasing thresholds were estimated to be 17 mJ/cm2 and 11 mJ/cm2, respectively.

Highly resolved fluorescence and phosphorescence excitation and emission spectra and two-dimensional total luminescence spectra of tetrabenzonaphthalene (TBN) in the Shpol'skii-type matrices n-hexane and n-heptane were measured at 4.2 K. Two different vibrational patterns could be observed in the multisite spectra under site-selective excitation and emission conditions. These patterns are attributed to two TBN stereoisomers with non-planar geometries D2 and C2h, occupying different sites in the polycrystalline matrices. A vibrational analysis of the most intense excitation and emission subspectra was performed, providing the fundamental frequencies of one stereoisomer in the S0 and S1 states. The energies of the singlet states of the TBN molecules calculated for D2 and C2h geometry are compared with experimental data.

Quasilinear absorption, fluorescence and phosphorescence spectra of 7,8,8a,9,10,10c-hexahydrohexahelicene (HHHL) were obtained in a polycrystalline n-pentane matrix at 77 K. 1,2-dimethylnaphthalene fundamental vibration frequencies appear in the emission spectra of HHHL. No exciton splitting of lines in the electronic spectra of HHHL was detected. Both naphthalene units of the HHHL molecule, almost perpendicular to each other, are coupled very weakly. The phosphorescence to fluorescence quantum yield ratio is greater for HHHL than for naphthalene and amounts of 0.16. Multiplet structure of quasilinear HHHL spectra has been discussed.

Quasilinear absorption and luminescence spectra of 1,2-benzotetraphene were obtained in polycrystalline matrices at 77 K. Tne energies of successive excited singlet states as well as the energy of the lowest excited triplet state were found experimentally and compared with those calculated by the PPP CI method. The fluorescence lifetime and quantum yield were determined experimentally. Moreover, the radiationless transition probabilities, lifetime of triplet state and phosphorescence quantum yield were estimated employing the Siebrand-Williams model. The results obtained suggest that radiationless ISC processes are the main deactivation channel of the S 1 and T 1 states. The vibrational analysis of quasilinear absorption and luminescence spectra was performed and fundamental frequencies of ground and first excited singlet states were determined.

Quasilinear absorption and fluorescence spectra of 1,2-dimethylnaphthalene (1,2-DMN) were obtained in a polycrystalline n-hexane matrix, at 4.2 K. The vibrational analysis of the spectra was carried out and fundamental frequencies of ground and first excited states were determined. The equilibrium geometries, normal coordinates and vibrational frequencies of the 1,2-DMN molecules in the So and S1 states were calculated by applying the QCFF/PI method. The Franck—Condon factors were evaluated and the frequencies and intensities of the observed transitions were compared with the calculated ones. The differences between the vibrational structure of 1,2-DMN and naphthalene spectra below 1100 cm−1 are mainly due to the mixing between ag or b3g naphthalene modes with other skeletal ones having out-of-plane contributions in the low-frequency range. The role of the coupled in-phase torsion of the two CH3 groups is discussed.

The reversible photocyclization reaction of [5]helicene to dihydrobenzoperylene (DHBP) was studied in the Shpolskii matrices n-pentane and n-hexane at 4.2 K. The well-resolved transitions from the photochemical product are attributed to DHBP, occupying a distinct site in n-hexane. The photoinduced formation of DHBP at 4.2 K was monitored during illumination by sequentially recording fluorescence spectra. The multiplet structure of [5]helicene and DHBP in fluorescence and in phosphorescence in n-pentane were determined by high-resolution total luminescence spectroscopy (TLS). The subsequent dehydrogenation of DHBP to benzoperylene (BP), which occurs rapidly at higher temperatures in fluid media and in the presence of hydrogen acceptors, was found to be inhibited in solid matrices.

Quasilinear absorption and fluorescence spectra of 1,2-dimethylnaphthalene (1,2-DMN) were obtained in a polycrystalline n-hexane matrix, at 4.2 K. The vibrational analysis of the spectra was carried out and fundamental frequencies of ground and first excited states were determined. The equilibrium geometries, normal coordinates and vibrational frequencies of the 1,2-DMN molecules in the So and S1 states were calculated by applying the QCFF/PI method. The Franck—Condon factors were evaluated and the frequencies and intensities of the observed transitions were compared with the calculated ones. The differences between the vibrational structure of 1,2-DMN and naphthalene spectra below 1100 cm−1 are mainly due to the mixing between ag or b3g naphthalene modes with other skeletal ones having out-of-plane contributions in the low-frequency range. The role of the coupled in-phase torsion of the two CH3 groups is discussed.