Absorption Spectra Of Porphyrins Research Articles

Understanding structure–properties relationships of porphyrin linked to graphene oxide through π–π-stacking or covalent amide bonds

Two graphene oxide nanoassemblies using 5-(4-(aminophenyl)-10,15,20-triphenylporphyrin (TPPNH2) were fabricated by two synthetic methods: covalent (GO-CONHTPP) and noncovalent bonding. GO-CONHTPP was achieved through amide formation at the periphery of GO sheets and the hybrid material was fully characterized by FTIR, XPS, Raman spectroscopy, and SEM. Spectroscopic measurements together with theoretical calculations demonstrated that assembling TPPNH2 on the GO surface in DMF-H2O (1:2, v/v) via non-covalent interactions causes changes in the absorption spectra of porphyrin, as well as efficient quenching of its emission. Interestingly, covalent binding to GO does not affect notably neither the porphyrin absorption nor its fluorescence. Theoretical calculations indicates that close proximity and π–π-stacking of the porphyrin molecule with the GO sheet is possible only for the non-covalent functionalization. Femtosecond pump–probe experiments revealed that only the non-covalent assembly of TPPNH2 and GO enhances the efficiency of the photoinduced electron transfer from porphyrin to GO. In contrast to the non-covalent hybrid, the covalent GO-CONHTPP material can generate singlet oxygen with quantum yields efficiency (ΦΔ = 0.20) comparable to that of free TPPNH2 (ΦΔ = 0.26), indicating the possible use of covalent hybrid materials in photodynamic/photothermal therapy. The spectroscopic studies combined with detailed quantum-chemical analysis provide invaluable information that can guide the fabrication of hybrid materials with desired properties for specific applications.

Ethyne Functionalized Meso-Phenothiazinyl-Phenyl-Porphyrins: Synthesis and Optical Properties of Free Base Versus Protonated Species.

Synthesis, structural characterization and photophysical properties for a series of new trans-A2B2- and A3B-type ethynyl functionalized meso-phenothiazinyl-phenyl porphyrin derivatives are described. The new compounds displayed the characteristic porphyrin absorption spectra slightly modified by weak auxochromic effects of the substituents and fluorescence emission in the range of 651–659 nm with 11–25% quantum yields. The changes recorded in the UV-vis absorption spectra in the presence of trifluoroacetic acid (TFA) are consistent with the protonation of the two internal nitrogen atoms of the free-base porphyrin (19 nm bathochromic shift of the strong Soret band and one long wave absorption maxima situated in the range of 665–695 nm). Protonation of the phenothiazine substituents required increased amounts of TFA and produced a distinct hypsochromic shift of the long wave absorption maxima. The density functional theory (DFT) calculations of a porphyrin dication pointed out a saddle-distorted porphyrin ring as the ground-state geometry.

Porphyrins and flavins as endogenous acceptors of optical radiation of blue spectral region determining photoinactivation of microbial cells

It is shown that exposure of suspensions of gram-positive Staphylococcus aureus, gram-negative Escherichia coli and yeast-like fungi Candida albicans to laser radiation of blue spectral region with 405 and 445 nm causes their growth inhibition without prior addition of exogenous photosensitizers. It is experimentally confirmed that compounds of flavin type capable of sensitizing the formation of reactive oxygen species can act as acceptors of optical radiation of blue spectral region determining its antimicrobial effect along with endogenous metal-free porphyrins (the role of endogenous porphyrins has been confirmed earlier by a number of researchers).The participation of these compounds in the antimicrobial effect of laser radiation is supported by the registration of porphyrin and flavin fluorescence in extracts of microbial cells upon excitation by radiation used to inactivate the pathogens. In addition, the intensity of the porphyrin fluorescence in extracts of microbial cells in the transition from radiation with λ = 405 nm to radiation with λ = 445 nm decreases by 15–30 times, whereas the photosensitivity of the cells under study in this transition decreases only 3.7–6.2 times. The contribution of porphyrin photosensitizers is most pronounced upon exposure to radiation with λ = 405 nm (absorption maximum of the Soret band of porphyrins), and flavins – upon exposure to radiation with λ = 445 nm (maximum in the flavin absorption spectrum and minimum in the absorption spectrum of porphyrins). The ratio between the intensity of the porphyrin and flavin components in the fluorescence spectrum of extracts depends on the type of microbial cells.

Binding Mode of Cationic Porphyrin with CT-DNA: Importance of the Location and the Number of Positively Charged of Periphery Cationic Ions of Porphyrin.

The binding modes of o-, m-, and p-trans-BMPyP with DNA were studied using their spectroscopic properties. Also, the binding modes were compared based on the location and number of periphery cationic methylpyridine ions of the cationic porphyrins. The optical absorption spectra of the o-, m-, and p-trans-BMPyP when bound to DNA presented red shifts and hypochromicity compared to the optical absorption spectrum of DNA-free cationic porphyrins. m-trans-BMPyP–DNA presented the largest red shifts and hypochromicity. The results of the circular dichroism spectral analysis indicated positive and negative bisignate absorption bands in the Soret band of the porphyrins in the case of all concentration ratios of o- and p-trans-BMPyP–DNA, and two negative absorption bands were observed in m-trans-BMPyP–DNA. Compared to the size of the absorption band of the DNA optical absorption spectrum, the results of the reduced linear (LDr) spectral analysis indicated mainly small sizes of Soret absorption bands (the absorption spectrum of porphyrins) and positive LDr values for o- and p-trans-BMPyP–DNA. In consideration of several of such spectroscopic properties, the binding of o- and p-trans-BMPyP with DNA can be said to be distant to insertion modes. Although the case of m-trans-BMPyP to DNA is an insertion mode, the m-trans-BMPyP molecular surface presented much tilt within the intercalation pocket. The results of comparing the binding modes of TMPyP having four periphery cationic methylpyridine ions of cationic porphyrin indicated that regardless of the number of periphery cationic methylpyridine ions of cationic porphyrin, in the case of the ortho-position, nonplanarity due to steric hindrance of the periphery cationic methylpyridine ions presented outside or groove-binding modes indicative of interaction with DNA phosphates. Unlike the ortho-position, the para-position presented different binding modes based on the number of periphery cationic methylpyridine ions. Only cationic porphyrins having four periphery cationic methylpyridine ions were inserted into the DNA. Lastly, regardless of the number of periphery cationic methylpyridine ions, all meta-positions were inserted into the DNA. This indicated that at the least the location and the number of periphery cationic methylpyridine ions of the porphyrins used in this experiment were important elements that determine insertion into DNA base pairs.

Efficient Energy Transfer (EnT) in Pyrene- and Porphyrin-Based Mixed-Ligand Metal–Organic Frameworks

Designing and synthesizing the ordered light-harvesting systems, possessing complementary absorption and energy-transfer process between the chromophores, are essential steps to accomplish successful mimicking of the natural photosynthetic systems. Metal-organic frameworks (MOFs) can be considered as an ideal system to achieve this due to their highly ordered structure, superior synthetic versatility, and tailorable functionality. Herein, we have synthesized the new light-harvesting mixed-ligand MOFs (MLMs, MLM-1-3) via solvothermal reactions between a Zr6 cluster and a mixture of appropriate ratio of 1,3,6,8-tetrakis(p-benzoic acid)pyrene and [5,10,15,20-tetrakis(4-carboxy-phenyl)porphyrinato]-Zn(II) ligands. The identical symmetry and connectivity of the two ligands of the MLMs was the key parameter of successful synthesis as a single MOF form, and the ample overlap between the emission spectrum of pyrene and the absorption spectrum of porphyrin provided the ideal platform to design an efficient-energy transfer (EnT) process within the MLMs. We obtained the nanoscale maps of the fluorescence intensities and lifetimes of microsize MLM grains for unambiguous visualization of EnT phenomena occurring between two ligands in MLMs. Moreover, due to complementary absorption and energy transfer between the two ligands in the MLMs, our MLMs performed as superior photoinduced singlet-oxygen generators, verifying the enhanced light-harvesting properties of the pyrene- and porphyrin-based MLMs.

Structural, spectroscopic and electrochemical investigations on fluorinated meso-tetraaryl porphyrins

Two series of meso-phenyl fluorinated porphyrins and their metal complexes, 5,10,15,20-tetrakis(2[Formula: see text],4[Formula: see text],6[Formula: see text]-trifluorophenyl)porphyrin, MT(2[Formula: see text],4[Formula: see text],6[Formula: see text]-TFP)Ps (2a–2d) and 5,10,15,20-tetrakis[3[Formula: see text],5[Formula: see text]-bis(trifluoromethylphenyl)]porphyrin, MT(3[Formula: see text],5[Formula: see text]-BTFMP)Ps (3a–3d); where M [Formula: see text] 2H; Ni(II); Cu(II) and Zn(II) have been synthesized and characterized using various spectroscopic techniques including UV-visible, fluorescence and [Formula: see text]H NMR and mass spectrometry. Electronic absorption spectra of porphyrins show the typical Soret (B) and visible (Q) bands. Free ligands and zinc(II) derivatives display two well-defined emission bands around 600–660 nm and 650–720 nm upon exciting the Soret band. Porphyrins, 1d, 2a, 2b, 2c, 3a and 3d were structurally characterized by single crystal XRD analysis, and various intermolecular interactions present in them were quantified on the basis of Hirshfeld surfaces and 2D fingerprint plots. Electrochemical studies were performed and the HOMO–LUMO energy gap is high for all the porphyrins compared to MTPPs.

Size-Dependent Optical Properties of Grana Inside Chloroplast of Plant Cells.

Well-packed thylakoids known as grana are one of the major functional sites for photosynthesis in algae and plants. Their highly ordered structures can be considered as a few hundred nanometer-sized particles having distinct scattering cross sections from other various macromolecular organizations inside plant cells. With this background we show that elastic light scattering imaging and microspectroscopy is an important tool for investigating structure and organization of grana inside a single chloroplast in plant cells. We have demonstrated this noninvasive method to identify the distribution of grana in intact fresh leaf of robust and rapidly growing Egaria densa, which is also known as Anachris and among the most popular aquarium plants. The scattering efficiency spectra of their individual grana fairly resemble cooperative absorption spectra of porphyrins and carotenoids. We found that the electronic structure of the stacked thylakoids shows granum size-dependence, indicating that size of grana is one of the critical parameters in the regulation of the photochemical functions in the thylakoid.

The origin of the absorption spectra of porphyrin N- and dithiaporphyrin S-oxides in their neutral and protonated states.

meso-Tetraphenylporphyrin N-oxide (1) and meso-tetraphenyl-21,23-dithiaporphyrin S-oxide (3) possess optical spectra that are distinctly different from their parent porphyrins, meso-tetraphenylporphyrin (2) and meso-tetraphenyl-21,23-dithiaporphyrin (4), respectively. The hyperporphyrin spectra were reproduced and classified using TD CAM-B3LYP and SCS-CC2 computational methods. Calculations revealed the electronic and conformational influences of the N- and S-oxide functionalities. While the N-oxide under acidic conditions forms a dication with a UV-vis spectrum that is nearly indistinguishable from that of the diprotonated parent porphyrin, the diprotonated S-oxide possesses a much different UV-vis spectrum from diprotonated parent dithiaporphyrin. A computational study of the protonation events revealed the site and degree of protonation and rationalized the regular and hyperporphyrin UV-vis spectra of the neutral and protonated species, respectively. The study illuminates the electronic effects of the relatively rare modification of the inner porphyrin heteroatoms. It also illustrates a case in which TD CAM-B3LYP reaches its limits to make reliable predictions about the optical properties of a porphyrinoid, making the use of higher methods essential.

Exploration of charge transfer and absorption spectra of porphyrin–polyoxometalate hybrids to search for high performance sensitizers

Lindqvist-, Keggin-, and Anderson-type polyoxometalate organic–inorganic hybrids were designed to investigate their charge transfer character and screen them as high performance p-type sensitizers.

Theoretical model for optical properties of porphyrin.

We propose a simple model to interpret the optical absorption spectra of porphyrin in different solvents. Our model successfully explains the decrease in the intensity of optical absorption at maxima of increased wavelengths. We also prove the dependence of the intensity and peak positions in the absorption spectra on the environment. The nature of the Soret band is supposed to derive from π plasmon. Our theoretical calculations are consistent with previous experimental studies.

Spectroscopic evidence of xanthine compounds fluorescence quenching effect on water-soluble porphyrins

The formation of π-stacked complexes between water-soluble porphyrins: 4,4′,4″,4″′-(21H,23H-porphine-5,10,15,20-tetrayl)tetrakis-(benzoic acid) (H2TCPP), 5,10,15,20-tetrakis(4-sulfonatophenyl)-21H,23H-porphine (H2TPPS4), 5,10,15,20-tetrakis[4-(trimethylammonio)phenyl]-21H,23H-porphine tetra-p-tosylate (H2TTMePP), 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine tetra-p-tosylate (H2TMePyP), the Cu(II) complexes of H2TTMePP and H2TMePyP, as well as chlorophyll a with xanthine, theophylline (1,3-dimethylxanthine) and theobromine (3,7-dimethylxanthine) has been studied analysing their absorption and steady-state fluorescence spectra in aqueous (or acetone in case of chlorophyll a) solution. During titration by the compounds from xanthine group the bathochromic effect in the porphyrin absorption spectra as well as the hypochromicity of the porphyrin Soret maximum can be noticed. The fluorescence quenching effect observed during interactions in the systems examined suggests the process of static quenching. The association and fluorescence quenching constants are of the order of magnitude of 103−102mol−1. The results obtained show that xanthine and its derivatives can quench the fluorescence of the porphyrins according to the number of methyl groups in the molecule of quencher.

Effect of Axial Ligand on the Binding Mode of M-Meso-Tetrakis(N-Methylpyridinium-4-Yl)Porphyrin to DNA and their Efficiency as an Acceptor in DNA-Mediated Energy Transfer

The binding modes of cationic porphyrins, namely M-meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (MTMPyP, where M=free base, Cu(II), Ni(II), Co(III), Mn(III), V(IV)=O and Ti(IV)=O), to native DNA were systematically investigated by polarized light spectroscopies. At low [porphyrin]/[DNA] ratio, planar porphyrins including TMPyP, CuTMPyP and NiTMPyP exhibited intercalative binding mode. In the intercalation pocket, the molecular plane of porphyrin is skewed to a large extent. As the mixing ratio was increased the coupling of the electric transition moments of the intercalated porphyrins was observed. Coupling can occur between the porphyrins when they are separated at least two DNA base. The porphyrins with axial ligands, namely VOTMPyP, TiOTMPyP, MnTMPyP and CoTMPyP bind to the exterior of the DNA at a low [porphyrin]/[DNA] ratio. The angle of one the two electric transitions of the porphyrin is in the range of 56°∼59°, while the other is in the range of 59°∼65°. Increasing the porphyrin density resulted in the appearance of an interaction between the bound porphyrins. All porphyrins were able to quench the fluorescence of intercalated ethidium. The mechanism behind the energy transfer is, at least in part, the Forster type resonance energy transfer (FRET). The minimum distance in base pairs between ethidium and porphyrin required to permit the excited ethidium to emit a photon was the longest for CoTMPyP being 17.6 base-pairs and was the shortest for CuTMPyP and NiTMPyP at 8.0 base-pairs. The variation in the distance was almost proportional to the extent of the spectral overlap, the common area under emission spectrum of ethidium and absorption spectrum of porphyrin, supporting the FRET mechanism, while the effect of the orientation factor which was considered by relative binding geometry was limited.

Excited states absorption spectra of porphyrins – Solvent effects

We propose a combination of different techniques to obtain the absorption cross-section spectra of triplet- and singlet-states in porphyrin-like molecules. Two extensions of the Z-scan technique are employed (pulse train Z-scan and white-light Z-scan) together with absorbance spectroscopy and laser flash photolysis. This approach allowed us to investigate features of excited-states absorption of meso-tetrakis (methylpyridiniumyl) porphyrin (TMPyP) that revealed the influence of solvents on the vibronic structuration of the transitions assigned to triplet-states, probably caused by hydrogen bonds established between the porphyrin and solvent molecules.

ANTIPHAGE ACTIVITY OF ASYMMETRICALLYSUBSTITUTED PYRIDYLPORPHYRINS

Aim. Study of the new synthetic asymmetrically-substituted porphyrins antiviral properties with the use of bacteriophages as model viruses. Materials and methods. In this work the ability of 5,10,15-tri(N-methyl-4-pyridyl)-20-(n-nonyl) porphyrin free base and its zinc complex to inhibit staphylococcal phage, phage T4 and T7 activity had been studied. Bacteriophages were incubated in presence of studied porphyrins in the dark and during irradiation, and then plated using the standard double-layer method. Final porphyrin concentrations were 0,1 μМ, 1 μМ and 10 μМ. Porphyrin absorption spectra were recorded after incubation with phage suspension with spectrophotometer “Spekol-10” and then were digitized. Results. It was shown, that staphylococcal phage is more sensible to the porphyrin action. Porphyrin free base suppress its activity on 68% in the dark and 80% after photoactivation. Phage inactivation with porphyrin zinc complex reached up to 100% in the dark and after irradiation. Phage Т4 is more sensible to the porphyrins action in the dark. Decrease of the phage activity in the dark reached up to 68% in presence of porphyrin free base, and 88% in presence of porphyrin zinc complex, and 24% and 35%, respectively, after photoactivation. Inversely, phage Т7 is more sensible to the photoactivated compounds action. Decrease of its activity in the dark reached up 21% in presence of porphyrin free base, and 16% in presence of porphyrin zinc complex, and 28% and 53%, respectively, after irradiation. Spectroscopic studies show that studied porphyrins bind to the phage nucleoproteins. Conclusion. Synthetic asymmetrically-substituted porphyrins affect the studied bacteriophage activity due to complex formation with phage particles.

Low‐irradiance red LED traffic lamps as light source in PDT for actinic keratoses

LED light sources for photodynamic therapy have become increasingly popular due to their narrow emission spectra that accurately match the absorption spectrum of porphyrins. Photodynamic therapy at low fluence rates has been shown to be as effective as high output irradiation for treatment of non-melanoma skin cancers. Fifteen patients with multiple non-hypertrophic actinic keratoses covering the scalp and the face were treated with aminolaevulinic acid photodynamic therapy using ordinary red LED traffic lamps as light source. All 15 patients improved clinically after one photodynamic therapy session. Only two patients required a second session to obtain satisfactory remission. Pain was minimal during these sessions. Red LED traffic lights constitute a simple alternative to far more complicated and expensive PDT light sources.

Systematic Investigation on the Central Metal Ion Dependent Binding Geometry of M-meso-Tetrakis(N-methylpyridinium-4-yl)porphyrin to DNA and Their Efficiency as an Acceptor in DNA-Mediated Energy Transfer

Binding geometry to DNA and the efficiency as a donor for energy transfer of various metallo- and nonmetallo-porphyrins were investigated mainly by polarized light spectrscopy and fluorescence measurements. Planar porphyrins including nonmetallo meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP), CuTMPyP, and NiTMPyP produced large red-shift and hypochromism in absorption spectrum and a negative circular dichroism (CD) in the Soret band suggesting that these porphyrins intercalate between DNA base-pairs as expected. In the intercalation pocket, the molecular plane of these porphyrins tilts to a large extent. From a linear dichroism (LD) study, the angle between the two electric transition moments in the Soret band were 16°, 12°, and 11° for TMPyP, NiTMPyP, and CuTMPyP, respectively. On the other hand, porphyrins with axial ligands namely, VOTMPyP, TiOTMPyP, and CoTMPyP, produced a positive CD signal in the Soret band. Hyperchromism and less red-shift were apparent in the absorption spectrum. These observations indicated that the porphyrins with an axial ligand bind outside of the DNA. The angles of both the B(x) and B(y) transition with respect to the local DNA helix were 39°~46° for all porphyrins. From these results, the conceivable binding site of porphyrins with axial ligands is suggested to be the minor groove. All porphyrins were able to quench the fluorescence of intercalated ethidium. Strong overlap between emission spectrum of ethidium and the absorption spectrum of porphyrins when they simultaneously bound to DNA was found suggesting the mechanism behind energy transfer is, at least in part, the Förster type resonance energy transfer (FRET). The minimum distance in base pairs between ethidium and porphyrin required to permit the excited ethidium to emit a photon was the longest for CoTMPyP being 17.6 base pairs and was the shortest for CuTMPyP and NiTMPyP at 8.0 base pairs. The variation in the distance was almost proportional to the extent of the spectral overlap, the common area under emission spectrum of ethidium and absorption spectrum of porphyrin, supporting the FRET mechanism, whereas the effect of the orientation factor which was considered by relative binding geometry was limited.

A Systematic Study of Electrochemical and Spectral Properties for the Electronic Interactions in Porphyrin–Triphenylamine Conjugates

AbstractA series of mono‐, di‐, tri‐, and tetra‐triphenylamine (TPA)‐substituted porphyrinatozinc complexes have been synthesized to investigate their spectral and electrochemical properties. The varied shapes of absorption spectra of porphyrin–triphenylamine (Por–TPA) conjugates in comparison with tetramesitylporphyrinatozinc (ZnTMP) indicate that there are strong interactions between porphyrin and TPA moieties. In general, the electron‐donating capability of a substituent on TPA and the number of TPA derivatives that bond with porphyrin would cause Soret band broadening and intensification of the Q(0,0) band. Due to the antenna effect of these conjugates, the fluorescence quantum yields were enhanced when more TPA moieties were linked. Cyclic voltammetry and spectroelectrochemical methods revealed the redox properties of Por–TPA conjugates. Axial ligation of porphyrinatozinc with N‐methylimidazole was useful in differentiating the oxidation site of Por–TPA conjugates. The first one‐electron oxidations of these conjugates are at the porphyrin ring. The charge‐transfer bands present in the near‐IR region in the absorption spectra of Por–TPA radical cations are evidence of an electronic interaction between porphyrin and TPA. The electron‐donating strength of the TPA group and the symmetry of the Por–TPA conjugate affect the intensity of the charge‐transfer band.

Layer-by-layer assembly of Zn(ii) and Ni(ii) 5,10,15,20-tetra(4-ethynylphenyl)porphyrin multilayers on Au using copper catalyzed azide-alkyne cycloaddition

We have developed a versatile layer-by-layer (LbL) fabrication method to assemble porphyrin based multilayer thin-films on electron-beam evaporated Au surfaces utilizing copper(I) catalyzed azide-alkyne cycloaddition (CuAAC) as both a means of anchoring the films to the Au surface and coupling the individual molecular layers together. The molecular based multilayer films are comprised of Zn(II) and Ni(II) 5,10,15,20-tetra(4-ethynylphenyl)porphyrin and a bis-azido linker layer. Herein, we describe the fabrication and characterization of multilayer films on Au surfaces modified with an azido-terminated alkanethiol self assembled monolayer. The absorbance growth trends, as followed by UV-vis absorption, show a consistent linear increase that extends over tens of bilayers. Multilayer film thicknesses were obtained from spectroscopic ellipsometry, using a Cauchy model applied over the transparent range, and resulted in a consistent linear growth trend. Optical constants, index of refraction and extinction coefficients, were then determined using an oscillator model over the entire visible region. The resulting extinction coefficients were consistent with those typical of Zn(II) and Ni(II) porphyrin absorption spectra. The topology of the films and surface roughness was analyzed by tapping mode atomic force microscopy (TM-AFM) and confirmed the continuous nature of the films. X-Ray photoelectron spectroscopy (XPS) was consistent with the expected elemental composition of the porphyrin based films assembled on Au surfaces. Additionally, XPS was used to examine the utility of ethylenediaminetetraacetic acid disodium salt (Na2EDTA) as a Cu chelator to remove adventitious catalyst following multilayer fabrication.

Photophysical Investigation of Neutral and Diprotonated Free-Base Bis(Arylethynyl)porphyrins

The photophysical properties for a series of free-base arylethynyl porphyrins and the corresponding trans-disubstituted tetraphenylporphyrin (H(2)TPP) derivatives lacking arylethynyl functionalities have been studied via electronic absorption and emission spectroscopy in both neutral and diacid forms. Enhanced substituent effects on porphyrin absorption spectra are observed in the arylethynyl porphyrins relative to the H(2)TPP derivatives, owing to the presence of the ethynyl spacer that allows for a coplanar geometry between the porphyrin macrocycle and the appended phenyl substituents. Upon protonation, both series of porphyrins exhibit substantially red shifted absorption and emission spectra and enhanced oscillator strengths, with the magnitude of the spectral shifts being more substantial in the presence of the ethynyl functionalities. Spectral features of the arylethynyl porphyrin bearing p-dimethylamino substituents closely resemble those previously classified as "hyperporphyrin spectra" and are indicative of excited-state charge-transfer character. Protonation of both series of porphyrins results in reduced fluorescence lifetimes and enhanced nonradiative decay rates, and the impact of protonation on these parameters is attenuated in the presence of the arylethynyl functionalities. Our results coupled with previous structural data showing that arylethynyl porphyrins exhibit less structural distortion upon diacid formation relative to H(2)TPP further substantiate the proposal that significant alteration of porphyrin photophysical properties upon diacid formation can be attributed to nonplanar structural distortions induced by protonation.

Synthesis and characterization of porphyrin sensitizers with various electron-donating substituents for highly efficient dye-sensitized solar cells

A series of porphyrin dyes with an electron-donating group (EDG) attached at a meso-position (YD1–YD8) have been designed and synthesized for use as sensitizers in dye-sensitized solar cells (DSSC). The nature of the EDG exerts a significant influence on the spectral, electrochemical and photovoltaic properties of these sensitizers. Absorption spectra of porphyrins having an amino group show broadened Soret band and red-shifted Q bands with respect to those of reference porphyrin YD0. This phenomenon is more pronounced for porphyrins YD7 and YD8 that have a π-conjugated triphenylamine at the meso-position opposite the anchoring group. Upon introduction of an EDG at the meso-position, the potential for the first oxidation alters significantly to the negative whereas that for the first reduction changes inappreciably, indicating a decreased HOMO-LUMO gap. Results of density-functional theory (DFT) calculations support the spectroelectrochemical data for a delocalization of charge between the porphyrin ring and the amino group in the first oxidative state of diarylamino-substituted porphyrins YD1–YD4, which exhibit superior photovoltaic performance among all porphyrins under investigation. With long-chain alkyl groups on the diarylamino substituent, YD2 shows the best cell performance with JSC = 13.4 mA cm−2, VOC = 0.71 V, and FF = 0.69, giving an overall efficiency 6.6% of power conversion under simulated one-sun AM1.5 illumination.