Andrzej Boguta

Study of the influence of substituents on spectroscopic and photoelectric properties of zinc phthalocyanines

Abstract In this paper we describe conversion of light energy into electric energy in a photoelectrochemical cell containing zinc phthalocyanine (ZnPc) dyes. For all dyes investigated in liquid polyvinyl alcohol with dimethyl sulfoxide solution and located in the photoelectrochemical cell the following measurements have been done: absorption, fluorescence, photoacoustic spectra, photovoltaic spectra, kinetics of photocurrent and current–voltage characteristics. It has been shown that all dyes located in the photoelectrochemical cell are able to convert light into electric energy but with different effectiveness. The influence of substituted different peripheral groups to ZnPc core and the correlation between the molecular structure and effectiveness of solar to electric energy conversion were observed and described. The unique behavior of ZnPc substituted with fluorines was indicated.

Mixtures of synthetic organic dyes in a photoelectrochemical cell

Abstract Spectroscopic and photoelectric properties of phthalocyanine (Pc), tetranaphtyloporphyrin (TNP) and merocyanine (Me) and their mixtures have been studied. Dyes dissolved in polyvinyl alcohol in dimethylsulfoxide were immersed in a semiconducting/metallic photoelectrochemical cell. Absorption, fluorescence and photoacoustic spectroscopies have been used as methods to follow deactivation pathways of radiative and non-radiative processes of excited states as a competitive processes to charge separation process. The dependence of photovoltage signal on excitation wavelength (photovoltage action spectrum), kinetics of photocurrent rise and decay in second time scale have been presented. Electric parameters of the photoelectrochemical cell with dyes (conductivity, capacitance) and their mixtures in the dark and upon illumination have been estimated. It was shown that all investigated dyes are able to generate photosignal but the values of photocurrent generated were dependent on the dye used in the experiment. The complexity of photoconversion process in the electrochemical cell fulfilled with the dye mixtures has been discussed. The presence of Me dye was found to improve TNP photovoltaic effect, whereas weak enhancement of photoeffects were observed in photoelectrochemical cell based on Me and Pc. This different tetraphenyloporphyrin and Pc conversion effectiveness in the presence of Me was discussed in aspects of various mechanisms of interaction between dyes. It has been indicated that dye aggregation, energy transfer, charge recombination and other processes can lead to improvement or inhibition of the photovoltaic effects and of the conversion effectiveness depending on the composition of dyes embedded in an electrochemical cell.

Yield of intersystem (singlet-triplet) crossing in phthalocyanines evaluated on the basis of a time in resolved photothermal method

The yields of triplet state formation for seven various phthalocyanines (Pc) unsubstituted by metal and substituted by Mg, Zn, Cu and Al in dimethyl-sulfoxide (DMSO) solutions were compared on the basis of time resolved photothermal measurements. The sample with atmospheric oxygen and bubbled by nitrogen were investigated. Absorption, fluorescence, and steady state photoacoustic spectra (PAS) of the same samples were also measured. The yields of triplet state formation for most of metal substituted dyes were higher than for investigated metal-free dyes. The triplets for various dyes were differently quenched by oxygen. The possibility of the application of investigated dyes in photodynamic therapy and diagnosis was discussed.

Spectroscopic and photoelectric studies of phthalocyanines in polyvinyl alcohol for application in solar energy conversion

Phthalocyanines are synthetic dyes which are shown to be good photoconverters which can be applied in a photoelectrochemical cell constructed of semiconducting and metallic electrodes. By means of spectroscopic investigation (absorption,fluorescence and photoacoustics) we have followed spectral properties of phthalocyanines complexed with metals dissolved in polyvinyl alcohol solution in order to determine the pathways of deactivation of their excited states. Spectroscopic investigations were accompanied with photovoltaic/photocurrent and current-voltage characteristics of the photoelectrochemical cell with dyes. It has been shown that there is a correlation between dye fluorescence feature and dye ability to electric photoconversion. The comparison of new data for metallic phthalocyanines with those obtained for porphyrins is discussed.

Photovoltaic effects in substituted metal-free and metallic sulfophthalocyanines in the photoelectrochemical cell

Abstract Metal-free and magnesium phthalocyanines substituted with long (CH 2 CH 2 N + (CH 3 ) 3 CH 3 SO 4 − ) chains and amino/nitro groups have been investigated as photoconverters in a sandwich-like photoelectrochemical cell. Photoelectric (photovoltaic spectrum, photocurrent kinetics), electric (current–voltage characteristics) and spectroscopic studies (absorption, fluorescence, photoacoustics) have been presented. Magnesium phthalocyanine with amino group has been found as the best photosensitizer whereas metal-free phthalocyanine substituted with nitro group shows weak effectiveness in photocurrent generation. The correlation between spectroscopic/photoelectric properties and molecular structure of dyes is discussed.

Non-radiative deactivation pathways of subphthalocyanine and subnaphthalocyanine dyes and of their mixture.

Subphthalocyanine and subnaphthalocyanine dyes and their mixture were investigated by means of the spectroscopic and photoelectric methods. Absorption, fluorescence, steady-state and time-resolved photothermal measurements for the dyes and their mixture were done in order to get information about the radiative and non-radiative deactivation processes as competetive processes to charge separation. It was shown that energy transfer between the dyes improved the photocurrent generation in photoelectrochemical cells (PEC) based on In(2)O(3) and SnO(2) as an electrode. The possible participation of the dye triplet states in non-radiative processes was discussed.

Scanning force microscopy investigations of (semi)conductive surfaces coated with Langmuir-Blodgett dye layers

The morphology of semiconducting (In2O3 and SnO2) and metallic (Au) surfaces without organic dyes and when coated with the Langmuir–Blodgett (LB) dye layer was investigated with the scanning force microscopy (SFM) technique. In the experiments the following dyes were used: magnesium tetranaphtylporphyrin (MgTNP), magnesium phthalocyanine (MgPc) and lead phthalocyanine (PbPc). On the ground of the SFM results the roughness parameter of the surfaces and its change upon dye deposition was estimated. It was shown that images of the surface morphology are closely connected with the relation between the magnitude of the substrate grains and the geometrical size of the dye molecules. The substrates of the large grains (Au and SnO2) preserve their own topography after coating with the dye layer whereas the change in the morphology was observed for the substrate of low granularity (In2O3). Absorption spectroscopy (also in the polarized light) was used to determine the dye spectral species when the dye LB layers were deposited on the surface and the dye orientation with respect to the substrate surface. It was showed that only MgTNP was kept in the monomeric form whereas PbPc and MgPc tend to form the aggregated species. The tilt angle between the dye layer and the substrate was estimated. It was shown that MgTNP is the in-plane arrangement and PbPc and MgPc are oriented perpendicularly to the substrate surface. The correlation between the topography of the substrate surface and the molecular arrangement of dyes (orientation, aggregation) was shown and discussed.

Fluorescein and Phenolphthalein—Correlation of Fluorescence and Photoelectric Properties

Two phthalein dyes in aqueous polyvinyl alcohol solutions of pH 8.5 have been investigated: fluorescein and phenolphthalein. Competitive pathways of deactivation of their energetically excited states have been followed by the use of spectroscopic and photoelectric techniques. Radiative, nonradiative, and charge separation processes followed by electron transfer have been measured by absorption, fluorescence, and photoacoustic spectroscopy accompanied by photovoltage/photocurrent generation in a photoelectrochemical cell. It is shown that, despite their being only a slight difference in molecular structure between the two dyes, their spectral as well as photoelectric behavior is significantly different.

Photothermal methods as tools for investigation of weakly interacting non-fluorescent phthalocyanines

In this paper, we report the spectroscopic properties of two newly synthesized phthalocyanines when substituted with short and long alkyl chains dissolved in dimethyl sulfoxide. The dyes are non-fluorescent and show a weak tendency for dimer formation. The aggregation process is not clearly visible in the absorption spectra. Therefore, steady-state and time-resolved photothermal methods were applied to evaluate the existence of the dye aggregates and their influence on spectral parameters of the investigated dyes.

Photothermal Properties of 3-Substituted Benzanthrone Dyes

ABSTRACT The paper presents spectral properties of six 3-substituted benzanthrone dyes dissolved in ethanol. Absorption, fluorescence, photoacoustics and time-resolved photothermal spectroscopy were used to follow radiative and non-radiative deactivation pathways occurring in dyes with participation of their excited singlet and triplet states. Thermal deactivation parameters were evaluated. They show that global non-radiative deactivation of excited energy depends on a kind of peripheral groups attached to the main molecular core. The yields of triplet state population and times of thermal deactivation decay were estimated and discussed in terms of the conformational changes in dyes and the differences in the dye molecular structures.