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Resonance Raman scattering (RRS) spectra of the complexes of 5,10,15,20-tetrakis[4-(N-methylpyridyl)]porphyrin with Co(II) and Cu(II) (CoIITMpyP4 and CuTMpyP4) in various solvents and in complexes with DNA are studied. Under nanosecond pulsed excitation, additional lines have been found in the RRS spectra of CoIITMpyP4 in a dimethylformamide (DMF) solution containing formic acid as an impurity and in a complex with DNA. At the same time, such lines are absent in the spectra of CoIITMpyP4 in pure DMF, dimethyl sulfoxide, water, and alcohols under the same excitation conditions. To interpret the experimental data, we have calculated the structure and vibrations of the solvate complexes of CoIITMpyP4 and CuTMpyP4 with water, methanol, and formic acid in the ground and in excited states. Based on the obtained data, additional lines in the Raman spectra are assigned to the dd excited state corresponding to the d(z2) → d(x2 – y2) transition, the lifetime of which increases with the formation of complexes of CoIITMpyP4 with formic acid. According to the calculation results, this correlates with a decrease in rate constant kic of the internal conversion due to an increase in energy gap ΔE between the ground and dd states of CoIITMpyP4. A decrease in the kic value in the case of binding of CoIITMpyP4 and CuTMpyP4 to DNA is caused by the additional interaction of the extra-ligand water molecule with one of its bases directly or via several water molecules immobilized on DNA surface. This complicates the conformational rearrangement of the water molecule in the dd excited state, which gives rise to an increase in the ΔE value.

The study of the excited states and photophysical characteristics of β-nitro-tetraphenylporphyrin (TPP–NO2) has been carried out using resonance Raman scattering (RRS) spectroscopy and methods of the density functional theory. The appearance of new lines, the intensity of which depends on the composition of the matrix and excitation wavelength, has been found in the TPP–NO2 RRS spectra in the low-temperature matrix. The calculation of the vibrational states of TPP–NO2 allowed the linking of the additional lines with the asymmetric vibrations of the nitro group and valence C–C vibrations of the phenyl ring (Ph1) that was nearest to it. The activation of these modes is related to the specific features of the TPP–NO2 geometry in the charge transfer (CT) state from Ph1 to the porphyrin macrocycle. It has been concluded on the basis of the analysis of the data of the study of the RRS spectra and the results of calculations that use the СAM-B3LYP and wB97XD functionals that the CT states do not play a significant role in the TPP–NO2 fluorescence quenching, as previously assumed. The fluorescence quenching owes to strengthening channels of internal and inter-conversion by reducing the energy gaps ΔE(S1 – T1) and ΔE(S1 – S0) as well as increasing the spin-orbit coupling between the S1 and T1 states. It has been shown that TPP–NO2 is characterized by conformational heterogeneity both in the ground and in the excited states, which explains the absence of the monoexponentiality of fluorescence decay kinetics.

The present work gives an overview of the developments in surface-enhanced Raman scattering (SERS) with metal-coated porous silicon used as an active substrate. We focused this review on the research referenced to SERS-active materials based on porous silicon, beginning from the patent application in 2002 and enclosing the studies of this year. Porous silicon and metal deposition technologies are discussed. Since the earliest studies, a number of fundamentally different plasmonic nanostructures including metallic dendrites, quasi-ordered arrays of metallic nanoparticles (NPs), and metallic nanovoids have been grown on porous silicon, defined by the morphology of this host material. SERS-active substrates based on porous silicon have been found to combine a high and well-reproducible signal level, storage stability, cost-effective technology and handy use. They make it possible to identify and study many compounds including biomolecules with a detection limit varying from milli- to femtomolar concentrations. The progress reviewed here demonstrates the great prospects for the extensive use of the metal-coated porous silicon for bioanalysis by SERS-spectroscopy.

Nanostructured silver films with different thicknesses were prepared by vapor deposition onto the surface of the anodic aluminum oxide (AAO) template to be used as surface-enhanced Raman scattering (SERS) active substrates. Both the peak position of the surface plasmon resonance (SPR) band and SERS enhancement of silvered AAO samples displayed non-monotonous dependence on Ag layer thickness. Using 441.6 nm excitation and a water-soluble cationic porphyrin, Cu(ii)-tetrakis(4-N-methylpyridyl) (CuTMPyP4), as a SERS-reporting analyte, two maxima of the SERS enhancement were obtained for Ag layers of 15 and 120 nm thickness. Thickness dependencies have been analyzed taking into account the type of SPR modes identified by means of quasicrystalline approximation (QCA) of statistical theory of multiple scattering of waves and multi-Lorentzian deconvolution. The analysis revealed that SERS enhancement is related to the absolute magnitude of the distance between excitation wavelength and spectral position of collective SPR mode. It was shown that matching of excitation wavelength and the most intensive SPR modes with non-radiative decay, generated mainly by coherent interaction of higher-order plasmon resonant modes (quadrupole and octupole), plays a dominate role in SERS performance. Besides, it has been observed that more intense SERS signal can be obtained when the analyte deposited on the Ag/AAO substrate was excited through the AAO template rather than from the silvered side. Our results demonstrate that appropriate excitation geometry and fine-tuning of the optical properties of the Ag/AAO substrate by adjusting the thickness of the Ag layer with respect to particular excitation wavelength can contribute to more effective SERS enhancement.

A facile, one-step, and environmentally friendly fabrication of anisotropic gold nanostructures and size-controlled spherical silver nanoparticles (NP) using biopolymer pectin is reported. The reduction of Au and Ag ions was carried out at room temperature using an increasing concentration of pectin, which acts as the single source of reducing and stabilizing agent. The as-formed NPs were studied by UV-vis, infrared Fourier transform and surface-enhanced Raman spectroscopies, as well as transmission electron microscopy and energy dispersive X-ray spectroscopy. A high yield of anisotropic gold nanostructures was observed at low concentrations of pectin, while its increase results in the formation of smaller sharp edged perfect triangles with a considerable number of quasi-spherically shaped gold NP. On the other hand, the size of spherical silver NP decreased as the biopolymer concentration in the solution increased. The surface-enhanced Raman scattering enhancement of different NPs was evaluated using a Cu-complex of cationic tetrakis(4-N-methylpyridyl)porphyrin as a probe molecule at 441.6 and 532 nm excitation. Great enhancement of Raman signal was obtained with a pectin–silver NP and for most of them their levels were higher than that for the routinely synthesized citrate silver NP.

A highly sensitive method for the detection and quantitative evaluation of antimony(III) using the surface-enhanced Raman scattering (SERS) technique is demonstrated. The method is based on the analysis of SERS spectra intensity of antimony bound to phenylfluorone (Sb-PhF). Phenylfluorone is widely used as an organic reagent for the spectrophotometric determination of some heavy metals. For the SERS experiment a Sb-PhF complex was adsorbed onto the silvered porous silicon substrate. The significant degradation of the SERS signal was observed during measurements in the air. The time evolution of SERS spectra at ambient and degassed conditions was investigated to find an optimal regime for SERS measurements. The limit of Sb detection in degassed samples was determined to be near 1 ng/mL, which is one order of magnitude less than that attainable by the photometric approach. The linear range of the method to Sb(III) was found to a mass concentration range of 1–10 ng/mL. This approach permits an absolute quantity of Sb(III) to be detected at the picogram level (∼50 pg). It is remarkable that a very small sample volume (50 μL) is required for SERS analysis. Moreover this technique offers high selectivity owing to the distinctive vibrational features for the metallorganic complex and to the resonance character of Raman spectra. The proposed SERS-based detection of Sb is a fast and highly sensitive method for use in environmental and industrial waste monitoring as well as for forensic science to determine gunshot residue. We expect that the approach reported herein can be further extended to develop new detection techniques for other heavy metals.

Since its discovery surface enhanced Raman scattering (SERS) has been attracting a constantly increasing attention of the scientific community as this method demonstrates an extremely high sensitivity and allows detection of the lowest possible concentration of substances including biological specimens up to single molecule [1]. The enormous increase of the Raman signal is observed for the molecules adsorbed on the surfaces consisted of metallic nanoparticles (NPs), especially of the noble metals. The electromagnetic mechanism plays the most valuable role in such enhancement and is caused by plasmon resonance in the certain places on the metallic surfaces. Recently, use of ordered arrays of metallic nanovoids has been found to significantly improve reproducibility and enhancement of SERS signal due to specificity of the plasmon modes within metallic cavities which geometry is well controlled at the fabrication process [2, 3]. However, engineering of such arrays is often connected with an alternation of a number of liquid and dry operations which is desirable to avoid for technology simplification [4]. An urgent problem as well is still a development of the technology that provides an integration of SERS-active substrate with other elements on the single Si substrate. In the present work we propose fabrication of SERS-active metallic/macro porous silicon (PS) nanovoid arrays consisted of only electrochemical and electroless liquid steps. As an initial template we used PS formed by anodizing of p-Si (100) wafer in solution of HF:DMSO=10:46 at 8 mA/cm for 7 min. The depth and diameter of pores varied in the ranges 700-1200 nm and 500-1500 nm, respectively. It is in good agreement with the dimensions of nanovoids usually applied for SERS [24]. Two types of metallized nanovoids (single and hybrid) were fabricated by liquid deposition of Ag and Ni on PS. To form first type of substrate based on single metal (Ag), PS was immersed into the 3mM AgNO3+0.5M HF water solution for 40-200 min. As reaction of Ag reduction has positive standard potential, Ag ions attract electrons from Si atoms. In that way in water-based solutions Si is oxidized to SiO2 while Ag is reduced. The addition of HF provides removing of SiO2 for continuous supplying of Ag ions with electrons. To form hybrid metallization (Ag/Ni), Ni was electrochemically deposited on PS from the solution of 213 g/l NiSO4—7H2O+5 g/l NiCl2—6H2O+25 g/l H3BO3+3 g/l saccharin at 10 mA/cm 2 for 2.5 min. Such regime resulted in covering PS surface with continuous Ni film of 70 nm thickness. After that Ag was deposited by electroless method from the previously described solution for 5-30 min. The morphology and structure of the samples were studied with SEM Hitachi S-4800. SERS activity of substrates was tested using water-soluble CuTMpyP4 as an analyte compound. Raman spectra were registered with the spectrometer Solar TII DM160MS3504I, equipped with CCDdetector. The source of continuous excitation was the HeCd laser Liconix (λ=441.6 nm). Figure 1 shows typical spectra of CuTMpyP4 on the initial PS (a), Ag/PS (b) and Ag/Ni/PS (c). Both of metallized substrates demonstrated SERS-activity. However, hybrid metallization resulted in six orders of magnitude increase of the signal intensity in comparison to pure PS while Ag/PS provided enhancement of five orders of magnitude.

Plasmonic nanostructures demonstrating an activity in the surface-enhanced Raman scattering (SERS) spectroscopy have been fabricated by an immersion deposition of silver nanoparticles from silver salt solution on mesoporous silicon (meso-PS). The SERS signal intensity has been found to follow the periodical repacking of the silver nanoparticles, which grow according to the Volmer-Weber mechanism. The ratio of silver salt concentration and immersion time substantially manages the SERS intensity. It has been established that optimal conditions of nanostructured silver layers formation for a maximal Raman enhancement can be chosen taking into account a special parameter called effective time: a product of the silver salt concentration on the immersion deposition time. The detection limit for porphyrin molecules CuTMPyP4 adsorbed on the silvered PS has been evaluated as 10(-11) M.

We present the resonance Raman scattering and surface enhanced Raman scattering (SERS) spectra of a complex of antimony with phenylfluorone (Sb-PF). Using the quantum-mechanical density functional method, we have calculated the geometric structure and frequencies of vibrations of the Sb-PF molecule and proposed for the first time an interpretation of its Raman spectra. Based on analysis of spectral changes that occur upon formation of a complex of phenylfluorone with Sb, we have found lines—markers—that can be used for detection and quantitative determination of the content of antimony by the SERS spectroscopy method.

A study of the water-soluble cationic CoII-tetrakis(N-methyl-4-pyridiniumyl)porphyrin, CoIITMpyP(4), complexed with calf thymus DNA and synthetic double-stranded and single-stranded adenine and thymine containing polynucleotides, was carried out by resonance Raman (RR) and transient absorption spectroscopies. Under high intensity nanosecond pulsed excitation, transient ν4* and ν2* bands appear in the RR spectra of CoIITMpyP(4) in the presence of DNA, poly(dA-dT)2 and poly(dT). On the basis of picosecond transient absorption measurements the lifetime of the corresponding transient species, ascribed to CoIITMpyP(4) electronic excited states of charge transfer (CT) origin (π, dz2), was found to be 10 ± 4 ns, i.e. three orders of magnitude longer than the excited state lifetime of free CoII porphyrin in aqueous solution. Such a considerable lengthening of the CT state is interpreted in terms of electron transfer from the pyridyl groups to the core ring, owing to the rotation of these groups and subsequent molecular flattening necessary to accommodate the porphyrin within the minor groove nearby T and AT sites.

A method for fabricating surface-enhanced Raman scattering (SERS)-active substrates by immersion deposition of silver on a macroporous silicon (macro-PS) template with pore diameters and depth ranging from 500-1000 nm is developed. The procedure for the formation of nanostructured silver films in the layers of macro-PS was optimized. Silver particles of dimensions in the nano- and submicron-scale were formed on the external surface of the macro-PS immersed in the water-ethanol solution of AgNO3, while the inner pore walls were covered by smaller, 10-30 nm diameter, silver nanoparticles. Upon introducing the hydrofluoric acid to the reaction mixture, the size of nanoparticles grown on the pore walls increased up to 100-150 nm. Such nanostructures were found to yield SERS-signal intensities from CuTMpyP4 analyte molecules of the same order to those obtained from silvered mesoporous silicon reported previously. The tested storage stability for the silvered macro-PS-based samples reached up to 8 months. However, degradation of the SERS intensity under illumination by the laser beam during spectral measurements was observed. To improve the stability of the SERS-signal a hybrid structure involving graphene oxide deposited on the top of analyte molecules adsorbed on the Ag/macro-PS was formed. A systematic observation of the time evolution of the characteristic peak at 1365 cm-1 showed that the addition of the oxidized graphene layer over the analyte results in ∼2 times slower decay of the Raman intensity, indicating that the graphene coating can be used to enhance the stability of the SERS-signal from the CuTMpyP4 molecules.

We have optimized the procedure for preparation of nanostructured silver films on the surface of mesoporous silicon (PSi) to use them as active substrates in surface-enhanced Raman scattering (SERS) spectroscopy. The greatest enhancement of the SERS signal was observed for samples obtained when the silver was deposited on PSi from an aqueous AgNO3 solution with concentration 1⋅10–2 M over a 10–15 minute period. The detection limit for rhodamine 6G on SERS-active substrates prepared by the optimized procedure was 1⋅10–10 M. The enhancement factor for the SERS signal on these surfaces was estimated as ≈2⋅108. We have shown that SERS-active substrates based on mesoporous silicon are promising for detection and study of complex organic compounds, in particular tetrapyrrole molecules.

Electron-deficient metallocomplexes of dodeca- and octanitroporphyrins produced by the introduction of 8 β-nitro substituents or 8 β-nitro and a meta-nitro substituent on each meso-aryl ring of Zn (II) and Ni (II) [meso-tetra-(2,6-dichlorophenyl)porphyrin] (Zn8, Ni8 and Zn12, Ni12, respectively) and their air-stable reduced species have been characterized by steady-state absorption and Soret-excited resonance Raman spectroscopies. One-electron reduced species of the metallocomplexes were produced by three different procedures (in deprotonated tetrahydrofuran in air ambient, in tetralhydrofuran with the addition of piperidine in air ambient, and in contact with a sodium mirror under vacuum) and demonstrated similar absorption and RR spectra. It is concluded on the basis of the RR spectra that the one-electron reduction products of the studied polynitrosubstituted metalloporphyrins are π–anion radicals in character.

By the resonance Raman scattering spectroscopy (RRS) method, photoinduced processes involving cationic Ni-5,10,15,20-tetrakis(4-N-methylapyridiniumyl)porphyrin (Ni(TMpy-P4)) in a phosphate water buffer have been investigated. Excitation into different regions of the Soret band at wavelengths of 397, 423, 441.6, and 457.9 nm permitted separate investigation of the behavior of the 4- and 6-coordinated forms of Ni(TMpy-P4). It has been found that Ni(TMpy-P4) is characterized by two photoinduced processes: the deactivation of initially 4-coordinated Ni(TMpy-P4) is followed by the addition to it, as axial ligands, of two water molecules from the environment to form a nonequilibrium 6-coordinated form Ni(TMpy-P4)(H2O)2 in the ground state, whereas in the process of deactivation of the excited 6-coordinated complex there occurs a dissociation of the axial water ligands to form a nonequilibrium 4-coordinated complex Ni(TMpy-P4) in the ground state. Some of the 4-coordinated molecules of Ni(TMpy-P4) are deactivated through the excited B 1g *-state without undergoing extracoordination. Quantitative analysis of the RRS spectra using the global fitting method has shown that in the course of deactivation ∼33% of photoexcited 6-coordinated molecules of Ni(TMpy-P4)(H2O)2 retain their axial ligands, relaxing through the “dark” long-lived intermediate state of the 6-coordinated form.

Resonance Raman spectra (RRS) of Co(II)‐ and Co(III)‐5,10,15,20‐tetrakis(4‐N‐methylpyridinium)porphyrin ((CoII(Tmpy‐P4), and CoIII(TMPy‐P4)) in aqueous solutions at different pH as well as in organic solvents (methanol, ethanol, DMSO, DMF) are obtained. The increased sensitivity of the oscillation frequencies ν2, ν4, ν8, and ν6 — the “markers” of the oxidation state of a metal — to the nature of an axial ligand has been revealed. For CoIII(Tmpy‐P4), the shifts of the indicated frequencies in extracoordination have turned out to be twofold larger than those for CoII(Tmpy‐P4). The spectral effects observed are related to different electron influence of the extraligands on the π‐system of the porphyrin ring. In the case of Co(III)‐porphyrin, interaction of the dπ‐orbitals of the metal and the eg*‐orbitals of the macrocycle is more efficient since its ionic radius is smaller than for the Co(II)‐complex. For CoIII(Tmpy‐P4), a linear correlation between the oscillation frequencies ν2, ν4, ν8, and ν6 and the experimental Gutmann parameters characterizing the electron‐acceptor properties of solvents is found.

The resonance Raman scattering (RS) spectra of a series of nitro-substituted derivatives of the free base of tetraphenyl porphyrin that were obtained on continuous excitation near the Soret band have been investigated. For the molecules in which the NO2 group is located in the β-position of pyrrole rings or in the para-position of meso-phenyl substituents, an intense line of the mode within the range 1340–1355 cm−1 is discovered. Based on the obtained resonance RS spectra of the diprotonated derivatives of nitro-tetraarylporphyrins, it is assigned to symmetrical vibration of a nitro group (ν s NO2). Activation of the ν s NO2 vibration is indicative of the existence of the π-delocalization effect for a number of nitro-substituted porphyrins at which interaction between the molecular orbitals of the nitro-substituents and the porphyrin macrocycle occurs. Moreover, the π-delocalization is typical of both direct addition of a nitro-substituent to the porphyrin ring and of its binding via a meso-phenyl group. The results obtained demonstrate the informative value of the resonance RS spectroscopy for creating and studying model donor–acceptor systems with the participation of porphyrins.

2-NO2-5,10,15,20-tetraphenylporphyrin (H2TPP−NO2) is shown to exist in solution as an equilibrium mixture of two NH tautomers with different spectral and photophysical properties. At 77 K in a rigid glass solution the fluorescence spectra of the tautomers contain two well-resolved narrow bands that are slightly (∼300 cm-1) Stokes-shifted with respect to the corresponding QX00 absorption bands, with the spectrum of the more stable tautomer being ∼500 cm-1 red-shifted as compared to the spectrum of the less stable tautomer. At room temperature, the tautomers show almost identical broad and structureless fluorescence spectra, markedly red-shifted relative to the longest wavelength absorption band. The Stokes shift increases with an increase of solvent polarity, being as large as ∼2000 cm-1 in N,N-dimethylformamide. Fluorescence lifetimes of the tautomers are found to be markedly (about a factor of 2) different, with both decreasing with an increase of solvent polarity. The reasons for these peculiar fluorescence properties can be understood on the basis of semiempirical quantum chemical calculations. Charge-transfer (CT) states are found to be located between the porphyrinic Q and B states for both tautomers, and a different energy of the CT states gives rise to different fluorescence lifetimes of the tautomers. The calculations also predict a lowering of the QX state energy and an increase of its dipole moment μ with a decrease of the angle θ between the plane of the NO2 group and the porphyrin plane (relative to the ground-state equilibrium geometry with θ = 80°). We suggest that, in solution, such an increase in the μ value should result in an increase of the stabilization interaction between the polar porphyrin and solvent molecules and, consequently, in flattening of the QX state energy curve as a function of θ and a shift of the minimum of this curve to θ values less than 80°. Both quantum chemical calculations and picosecond transient absorption measurements of the S1 → Sn absorption show that the fluorescent QX state of H2TPP−NO2 has mainly 1(π,π*) character with a relatively small charge-transfer admixture.

SERS-active arrays of bimetallic nanovoids have been fabricated by Ni electrochemical plating followed by Ag immersion deposition on macroporous silicon (PS). Presence of HF in the solution for Ag deposition has been found to result in fabrication of the SERS-active substrates with 20 times enhanced Raman intensity in comparison with those formed in HF-free solution. The detection limit of R6G adsorbed on the bimetallic substrates has been determined to reach 10 M.

Photoreduction is observed for Fe III (TPP)Cl (TPP is tetraphenylporphyrin) in some oxygen (O)-containing solvents under anaerobic conditions using resonance Raman (RR) and absorption spectroscopy. This process is found to be initiated by visible light in the 390–450 nm region. The coincidence of RR and absorption spectra of photoinduced species and of chemically reduced ones reveals that the final product of photoreduction is the high-spin Fe II (TPP)L complex, where L = THF (tetrahydrofuran), DMF (dimethyl formamide) or 1,4-dioxane. Such a photoreduction is not observed under anaerobic conditions for the Fe III (TPP)Cl complex in benzene, pyridine or CH 2 Cl 2 , nor in the abovementioned solvents under aerobic conditions. No photoreduction is observed for Fe III (OEP)Cl (OEP = octaethylporphyrin). A mechanism for the photoinduced phenomenon observed for Fe III (TPP)Cl in O-containing solvents under anaerobic conditions is proposed.

Three types of Ag-coated arrays from porous anodic aluminum oxide (AAO) were prepared and studied as substrates for surface-enhanced Raman scattering (SERS). They were compared with Ag-coated porous silicon (PSi) samples. AAO-based substrates were prepared by the vapor deposition of silver directly onto the surface of porous AAO with different morphologies of the pores, whereas SERS-active island films on the PSi were prepared by immersion plating. The resulting metallic nanostructures were characterized by UV-vis absorption spectroscopy and scanning electron microscopy (SEM). Thermal evaporation leads to the formation of granular arrays of Ag nanoparticles on the surface of AAO. SERS activity of the substrates was tested using water-soluble cationic Zn(II)-tetrakis (4-N-methylpyridyl) porphyrin (ZnTMPyP4) as a probe molecule. The results indicate that all AAO-based substrates studied here exhibit some degree of SERS activity. Noteworthy, for excitation at 532 nm, signals from AAO-based substrates were comparable with those from the PSi-based ones, whereas for 441.6 nm excitation they were about twice higher. The strongest SERS-enhancement at 441.6 nm excitationwas provided by the AAO substrates with silver deposited on the monolith (originally nonporous) side of AAO. Preferential SERS-enhancement of the bands ascribed to the vibrations of the N-methylpyridinium group of ZnTMPyP4 when going to blue excitation was found. Copyright © 2010 John Wiley & Sons, Ltd.

Porous silicon (PS) prepared from n-type Si crystal is proposed as a new material for the fabrication of sensitive substrates for surface-enhanced Raman scattering (SERS). The formation procedure for nanostructured silver films on the surface of PS was optimized. Maximum of SERS enhancement for rhodamine 6G probing molecule is observed for samples obtained by the immersion plating from the water solution of AgNO 3 with the 10 mM concentration during 5 min. The dependence of morphological parameters of PS and corresponding silvered surfaces on the anodization current density has been studied. It is shown that the most SERS activities possess substrates produced from PS with lower porosity. The optimum of the PS layer thickness for high Raman signal is about 5 μm. The detection limit for rhodamine 6G adsorbed on Ag-coated PS from the 100 pM solution is established to be comparable with that for p-type PS-based substrates. Thus, the n-type porous silicon is suitable material for the preparation of sensitive SERS-active substrates.

A fabrication of the surface-enhanced Raman scattering (SERS) active substrates has been developed by immersion plating of the silver onto porous silicon (Ag- por -Si). Effects of the porous silicon morphology on the structure of the Ag films have been analyzed by scanning electronic microscope. Activity of the Ag-coated por-Si toward SERS was estimated using water-soluble porphyrins as analyte molecules. The Ag- por -Si samples were appeared to be sensitive and stable SERS-active substrates. It has been found that the variation of SERS signal scanned over the sample surface is less than 9%. Additionally, plates of Ag- por -Si displayed high sensitivity being stored within 1 month in the air. It was shown that even several minutes incubation of Ag- por -Si in solution is enough to obtain well-defined SERS signal. SERS spectra of the water-soluble cationic tetrakis(N-methylpyridyl)porphyrin (H 2 TMPyP4) and anionic tetrakis(sulfonatophenyl)porphyrin (H 2 TPPS) were compared with their resonance Raman (RR) spectra. For the cationic H 2 TMPyP4 the partial metallation has been detected during impregnation of the porphyrin molecules on the Ag- por -Si surface. In case of the anionic H 2 TPPS there was no evidence of the silver complex formation.

In the present work we study the spectral and photophysical properties of a relatively simple porphyrin system with an electron-withdrawing substituent, namely 2-nitro-5, 10, 15, 20-tetraphenylporphyrin (H2TPP-NO2). Similar β-nitro-substituted tetraaryl-porphyrins have been studied recently in [1–4], for which unusual fluorescence properties were reported. In particular, it has been shown that these compounds exhibit broad, structureless and significantly Stokes-shifted fluorescence spectra. The Stokes shift was found to increase with an increase of solvent polarity (dielectric constant). The authors [1–4] have interpreted this fluorescent state as having intramolecular chargetransfer (ICT) character of the [(P+) — (NO2)-] type. It has been even suggested [1, 3, 4] that the fluorescent state may be of the “Twisted Intramolecular Charge-Transfer” (TICT) origin, that corresponds to full electron transfer from the porphyrin ring to the NO2 group. The lifetimes of this unusual fluorescence state were found to be in the range of ∼1–3 ns [1–4].

Cationic complexes of 5, 10, 15, 20-tetrakis[4-(N-methylpyridyl)]porphyrin with cobalt(II) (CoII(TMpy-P4)) and cobalt(III) (CoIII(TMpy-P4)) in phosphate water buffer solution (PBS) (pH=6.8, μ=0.2) and in interaction with calf thymus DNA have been studied by absorption and resonance Raman spectroscopies.

The first attempts to obtain resonance Raman (RR) spectra of metalloporphyrin ir-anions1 and the works that followed24 showed that RR spectroscopy could be regarded as a method for studying the electronic structure of these compounds. This paper deals with the RR study of ir-anions of Zn-porphyrin complexes. We focus on the analysis of changes in the electronic structure, force field and ir-orders of bonds which take place in the porphyrin cycle as a result of successive single-electron reduction: from monoanion to tetraanion.

The transformation of metalloporphyrin molecules into their mono- and di-π-anions during contact of the metalloporphyrin solution with the Na and K metals has been examined by electronic absorption spectroscopy, ESR, 1 H and 13 C NMR, IR and Raman spectroscopy. The charge distribution is calculated by the CNDO/2 method. It is shown that the generation of anions is accompanied by characteristic changes in all the spectra and in the charge distribution. Hyperfine splitting in the ESR spectra of anion radicals of zinc complexes of monoaza- and diazaetioporphyrins is detected. ESR spectra are simulated on the basis of McConnel and Chesnut's relation and unpaired electron distribution. In 1 H NMR spectra of dianions large upfield shifts of proton signals under the influence of paramagnetic ring current are observed. The 13 C chemical shifts of neutral porphyrins correlate with the charge distribution, while those of the corresponding dianions are determined by changes in the mean average excitation energy, paramagnetic ring current, and electron density. The majority of the bands of IR and Raman spectra undergo a low-frequency shift on passing to anions. A comprehensive analysis reveals a qualitative picture of changes in specific bonds of a molecule and the electronic structure as a whole. These data are confirmed by quantum-chemical calculation of the electron density in dianions.

The paper covers two aspects: 1) regularities of manifestation of metalloporphyrin reduction by alkali metals (Na, K) in vibrational spectra (IR, resonance Raman spectra) and a possibility of determining the electron structure of ionization products using these data; 2) the usage of spectra variations in the series starting molecule-monoanion-dianion for matching up the bands in the spectra of deuterized modificationes, choosing the model of the force field, and determining the form of normal vibrations.