Photophysical Properties Of Porphyrins Research Articles

Анизотропия и спектроскопические свойства комплексов молекул мезо-тетра(4-карбоксифенил)порфирина с алмазными наночастицами

Meso-tetra (4-carboxyphenyl) porphyrin complexes with nano-sized diamonds were studied spectroscopically. The polarization characteristics of their steady-state fluorescence indicate the formation of a covalently bound complex between porphyrin molecules and diamond nanoparticles. The hydrodynamic volumes of the studied complexes were estimated on the basis of data on steady-state fluorescence anisotropy. Measurements have shown that the photophysical properties of porphyrin do not change significantly when an organo-inorganic hybrid complex with nanodiamonds is formed. The studied complexes can be promising in the field of biomedical research, in particular, for diagnostic purposes and for the development of new generation photosensitizers for practical medicine.

Photophysical properties of porphyrins with sterically distorted and partially screened macrocycles

We have experimentally studied the spectral-luminescent and photophysical properties, as well as interaction processes with molecular oxygen, of eclipsed β-alkyl-substituted porphyrins para-methoxyphenyl rings of which in opposite meso-positions of the macrocycle are linked with each other in the ortho-position with the (-OCH2)-Ph-(CH2O-) bridge. Using methods of the density functional theory, we have calculated the structures of these porphyrins in the ground and lowest triplet states, electronic transitions and vibrational states, and matrix elements of the direct spin-orbit interaction. It has been found that the lifetime of the T 1 state of the investigated compounds is noticeably shortened due to the enhancement of the internal conversion. This enhancement is caused by the conformational dynamics, which promotes increasing Franck-Condon factors and the spin-orbit interaction between the T 1 and S 0 states. Nevertheless, this does not lead to a considerable decrease in the singlet-oxygen formation quantum yield. We have calculated the structures of a porphin dimer and possible dimeric forms of examined porphyrins. It has been shown that distortion of the porphyrin macrocycle according to type of ruffling weakly affects the binding energy of the porphyrin macrocycles in the dimer, this effect being unable to prevent aggregation. At the same time, the screening of the macrocycle by the phenyl ring lowers the probability of formation of oligomeric structures, which, in view of the determined photophysical properties of investigated compounds, may be used in photochemical applications that require elevated concentrations of porphyrins.

Photophysical properties of porphyrins as a selection criterion of porphyrins for study of their effectiveness against microorganisms

Photophysical properties of porphyrins as a selection criterion of porphyrins for study of their effectiveness against microorganisms

Characteristic electronic perturbation by asymmetric arrangements of p-aminophenyl substituents in free-base porphyrins.

We have investigated the perturbed electronic properties of meso-substituted free-base porphyrins with symmetric and asymmetric arrangements of substituents using time-resolved spectroscopic measurements and theoretical calculations. The extent of electronic perturbation by substituents in meso-substituted porphyrins is mainly affected by the isoenergetic condition of frontier MOs of porphine and substituent units, nonorthogonal geometry, and geometrical arrangement of substituents. By using the asymmetric arrangements of p-aminophenyl and pentafluorophenyl substituents, we can induce the electron-rich condition on the porphine unit and the intramolecular charge transfer character in the excited state. On the basis of this work, we can gain further insight into the energetic and geometric factors of substituents, the interaction between porphine and substituent units, and the perturbed photophysical and electronic properties by substituents, which provides a firm basis for further understanding of the catalytic activities or photophysical properties of porphyrins in porphyrin-based molecular catalysts and electronics.

Egg-Citing! Isolation of Protoporphyrin IX from Brown Eggshells and Its Detection by Optical Spectroscopy and Chemiluminescence

A simple and cost-effective laboratory experiment is described that extracts protoporphyrin IX from brown eggshells. The porphyrin is characterized by UV−vis and fluorescence spectroscopy. A chemiluminescence reaction (peroxyoxalate ester fragmentation) is performed that emits light in the UV region. When the porphyrin extract is added as a fluor to this chemiluminescence reaction, an eye-catching deep red glow is emitted from the solution. Using a familiar object, an egg, the experiment touches upon many aspects in chemistry (natural products isolation, structure and photophysical properties of porphyrins, photochemistry). Focus is placed on the understanding of the optical properties of protoporphyrin that enable the final chemiluminescence experiment. This project is appropriate for upper-level organic chemistry students, but might also serve in the advanced physical chemistry laboratory to facilitate a more detailed discussion of photophysical phenomena. Finally, the chemiluminescence experiment is suitable as an impressive stand-alone demonstration.

Comparison of the resonance-enhanced multiphoton ionization spectra of pyrrole and 2,5-dimethylpyrrole: Building toward an understanding of the electronic structure and photochemistry of porphyrins

The photophysical properties of porphyrins have relevance for their use as light-activated drugs in cancer treatment and sensitizers in solid-state solar cells. However, the appearance of their UV-visible spectra is usually explained inadequately by qualitative molecular-orbital theories. We intend to gain a better insight into the intense absorption bands, and excited-state dynamics, that make porphyrins appropriate for both of these applications by gradually building toward an understanding of the macrocyclic structure, starting with studies of smaller pyrrolic subunits. We have recorded the (1+1) and (2+1) resonance-enhanced multiphoton ionization (REMPI) spectra of pyrrole and 2,5-dimethylpyrrole between 25 600 cm(-1) (390 nm) and 48 500 cm(-1) (206 nm). We did not observe a (1+1) REMPI signal through the optically bright (1)B(2) (pipi( *)) and (1)A(1) (pipi( *)) states in pyrrole due to ultrafast deactivation via conical intersections with the dissociative (1)A(2) (pisigma( *)) and (1)B(1) (pisigma( *)) states. However, we did observe (2+1) REMPI through Rydberg states with a dominant feature at 27 432 cm(-1) (two-photon energy, 54 864 cm(-1)) assigned to a 3d<--pi transition. In contrast, 2,5-dimethylpyrrole has a broad and structured (1+1) REMPI spectrum between 36 000 and 42 500 cm(-1) as a result of vibronic transitions to the (1)B(2) (pipi( *)) state, and it does not show the 3d<--pi Rydberg transition via (2+1) REMPI. We have complemented the experimental studies by a theoretical treatment of the excited states of both molecules using time-dependent density functional theory (TD-DFT) and accounted for the contrasting features in the spectra. TD-DFT modeled the photochemical activity of both the optically dark (1)pisigma( *) states (dissociative) and optically bright (1)pipi( *) states well, predicting the barrierless deactivation of the (1)B(2) (pipi( *)) state of pyrrole and the bound minimum of the (1)B(2) (pipi( *)) state in 2,5-dimethylpyrrole. However, the quantitative agreement between vibronic transition energies and the excited-state frequencies calculated by TD-DFT was hampered by inaccurate modeling of Rydberg orbital mixing with the valence states, caused by the lack of an asymptotic correction to the exchange-correlation functionals used.

Synthesis and photophysical properties of porphyrins with fluorenyl pendant arms

Symmetrical-A 4-porphyrins bearing four fluorene donor moieties TOFP (5,10,15,20-tetra(4-(2 methyloxyfluorenyl)phenyl)porphyrin) as well as eight fluorene arms OOFP (5,10,15,20-octa(3,5-(2-methyloxyfluorenyl)phenyl)porphyrin) were synthesized and characterized. Preliminary photophysical properties are reported. In comparison to the reference tetraphenylporphyrin TPP, the luminescence properties are slightly improved. The fluorescence quantum yields of tetrafluorenylporphyrin TOFP ( 1) and octafluorenylporphyrin OOFP ( 2) are 0.10 and 0.13, respectively.

Mesoscopic Donor−Acceptor Multilayer by Ultrahigh-Vacuum Codeposition of Zn-Tetraphenyl-Porphyrin and C70

The peculiar electrochemical and photophysical properties of porphyrin and fullerene molecules make them promising candidates for the construction of two- and three-dimensional organic-based materials. An important question is how pristine fullerene and porphyrin will organize when deposited on surfaces via in vacuum molecular beam evaporation. Here we show that codeposition of C(70) and Zn-tetraphenyl-porphyrin (ZnTPP) induces the self-assembly of electron-rich flat aromatic molecules at the curved surface of C(70), thus enhancing the chromophore interaction and forming a supramolecular multilayer donor-acceptor structure. While the ground-state electronic spectra almost reflect a simple summation of ZnTPP and C(70) components, the excited-state electrons at the porphyrin macrocycle can rapidly delocalize to the fullerene. The excited charge transfer time scale is faster than 1-2 fs, as shown by resonant photoemission for the core-excited charges.

Dextrin‐Microencapsulated Porphyrin: Luminescent Properties

Photophysical properties of porphyrins in aqueous solutions are strongly affected by aggregation. One possible solution to this problem is to encapsulate the porphyrin into polymeric spheres, to provide an environment where the photosensitizer can be administered in its monomeric form in such treatments as photodynamic therapy. Here we report the microencapsulation of the meso-tetrakis(4-sulphonatophenyl) porphyrin (TPPS(4)) photosensitizer by the ultrasonic spray-drying technique. The encapsulated TPPS(4) was morphologically characterized by scanning electron microscopy, and its photophysical properties were studied and compared with those of a physical blend of dextrin and TPPS(4). We successfully encapsulated TPPS(4) into dextrin microspheres, and the encapsulated photosensitizer displays higher luminescence intensity than that of the prepared physical blends.

Tuning of redox and photophysical properties of porphyrins by successive introduction of one, two, three and four meso-furyl groups

The electrochemical and photophysical studies were carried out on 12 meso-furylporphyrins with three porphyrin cores such as N 4, N 3S and N 2S 2. The studies supported a systematic variation of redox potentials, absorption and emission band shifts, quantum yields and lifetimes by successive replacement of one, two, three and four six membered meso-aryl groups of porphyrin with five membered meso-furyl groups. The maximum effects in electrochemical and spectral properties were observed for porphyrins with four meso-furyl groups.

Photophysical properties of boron-dipyrrin appended porphyrins with heteroatom cores

The photophysical properties of porphyrins with N 3S and N 3O cores appended with two boron-dipyrrin units and porphyrins with N 2S 2 and N 4 cores appended with four boron-dipyrrin units are described. The steady-state fluorescence measurements indicate that the energy transfer from boron-dipyrrin units to the porphyrin unit is efficient with N 4 and N 3O porphyrin cores and less efficient with N 3S and N 2S 2 cores. The energy transfer rates calculated from lifetime measurements are also in support with these observations.

Synthesis and photophysical properties of porphyrins containing viologen units for ultrafast molecular photonics

Several 5,15-diarylporphyrin derivatives containing viologen units as an electron acceptor for ultrafast intramolecular electron transfer have been synthesized. The fluorescence of the porphyrin–viologen linked systems was appreciably quenched by the attached viologens. In accordance with this, the formation of a charge-separated state was observed upon excitation with a femtosecond (fs) laser at 400 nm. The rate of electron transfer and back transfer was controlled by the different length of alkyl chain spacers between porphyrin and viologen. Attempts to use these porphyrin molecules as a thin film component of ultrafast parallel data processing by guided wave mode geometry were limited by gradual deterioration upon repeated fs laser excitation.

Photophysical properties of porphyrins, phthalocyanines, and benzochlorins

This work examines the photophysical properties of a series of porphyrin, phthalocyanine, and benzochlorin derivatives. The porphyrin group includes tetraphenylporphyrin, divinylporphyrin ether, dihematoporphyrin ether, the trivinylporphyrin ether, and the trihematoporphyrin ether. The phthalocyanine group includes phthalocyanine tetrasulfonate, chloroaluminum phthalocyanine tetrasulfonate, zinc phthalocyanine tetrasulfonate, and aluminum naphthalocyanine tetrasulfonate. The chlorins include octaethylbenzochlorin, zinc octaethylbenzochlorin, octaethylbenzochlorin sulfonic acid, and zinc octaethylbenzochlorin sulfonic acid. Ethyl etiopurpurin is also studied. The UV-Vis and fluorescence emission spectra, fluorescence quantum yields, fluorescence rate constants, radiative and singlet state lifetimes are compared for the series of compounds. Results indicate that while the octaethylbenzochlorin and phthalocyanine photosensitizers profile, this profile is very different from that observed for the porphyrin photosensitizers.

Aggregation effects on the photophysical properties of porphyrins in relation to mechanisms involved in photodynamic therapy.

The use of porphyrin preparations in conjunction with visible light in Photodynamic Therapy (PDT) is dependent on two important properties exhibited by these compounds, i.e. their preferential uptake and localisation in malignant tissue and the fact that such porphyrins are very efficient photosensitisers. By direct absorption of light they are electronically excited to higher energy levels from which they can, by energy transfer processes, donate this energy to acceptor molecules giving porphyrin deactivation and elevation of acceptor to excited states possibly not attainable by direct absorption under these conditions.