Spectroscopic analysis of porphyrin compounds irradiated with visible light in chloroform with addition of β-myrcene

Photodegradation of free base and zinc porphyrins in the presence and absence of oxygen

Comparison of photostability in degassed and aerated toluene solutions is reported for 5,10,15,20-tetraphenylporphyrin, 5,10,15-tri(p-tolyl)porphyrin, and their zinc analogues. After degassing, quantum yields of photodegradation are higher, but the photodecomposition rates decrease. Lower stability in deoxygenated solutions is due to much longer triplet lifetimes: 200-300 microseconds, compared to 200-360 ns in non-degassed toluene. For the zinc porphyrins, the LC-MS results show that the initial photoproduct contains two oxygen atoms. Based on electronic absorption and calculations, it is assigned to dehydrated zinc biladienone structure, relatively stable in toluene, but readily demetallated in dichloromethane. A similar species is formed also in the case of free bases, but it then undergoes hydration due to traces of water present in the solvent. Zinc derivatives were found to form biladienones even in degassed solutions. To explain this observation, we postulate formation of a complex with remaining oxygen or oxygen-containing species which is not removed by freeze-thaw procedure. This hypothesis is confirmed by MS results and by the analysis of photodegradation products obtained when zinc porphyrin is complexed with dimethylsulfoxide (DMSO). Under these circumstances, changes in absorption are the same as in the absence of DMSO when non-degassed toluene is used, but irradiation of deoxygenated solutions leads to a different photoproduct. For both degassed and non-degassed solvents, complexation with DMSO results in the enhancement of photostability.

Photophysics and visible light photodissociation of supramolecular meso-tetra(4-pyridyl) porphyrin/RuCl2(CO)(PPh3)2 structures

In the last decades, supramolecular structures have been explored in many technological efforts. One example of such supramolecules is attained when ruthenium complexes are attached in the outer sites of a porphyrin. Ruthenium complexes act as modulators of the photophysical processes of macrocyclic molecules. Besides the investigation of the main changes introduced by the ruthenium complexes in the electronic and vibronic properties, and in the excited state deactivation processes of porphyrins, discussions concerning the photostability of these supramolecules are much needed. Here, we investigate the supramolecular free-base meso-tetra(4-pyridyl) porphyrin decorated with "RuCl₂(CO)(PPh₃)₂" ruthenium species linked at each of its (4-pyridyl) moieties. The modifications in the photophysical processes introduced by the metallic outlying species are discussed and our results suggest an energy transfer process from the porphyrin B-band to the ruthenium complex MLCT-band. The demonstration of visible light photodissociation of the supramolecule, via both pulsed and continuous laser, is also addressed.

Two spectral QSPR models of porphyrin macromolecules for chelating heavy metals and different ligands released from industrial solvents: CH2Cl2, CHCl3 and toluene

Two simple and reliable correlations are introduced for the prediction of emission and absorption of porphyrins and their derivatives, i.e. metalloporphyrins and ligand coordinated metalloporphyrins. They can be used to sense the extracted precious metals. The proposed models require only simple structural parameters such as the number of carbon, metal and metal-free molecular fragments of desirable porphyrins or their derivatives. Since the proposed models depend on molecular structures of the desired compounds, they can be easily applied for complex molecular structures. Experimental data of 272 porphyrin derivatives were used to derive and test the novel models for the assessment of their emission (Em.) and absorption (Abs.) values in three solvents namely dichloromethane, toluene and chloroform. The values of the coefficients of determination (r ²) for the training set (183 compounds) in dichloromethane and three different test sets, corresponding to the three mentioned solvents, for the emission and absorption correlations were greater than 0.70. The calculated values of the root-mean-square error (RMSE) for the training sets of Em. and Abs. correlations were equal to 7.56 and 4.86 nm, respectively. Further statistical parameters also confirm the high reliability of the new models.

Fabrication of carbon nanotube-multiporphyrin array composites as light-sensitizer for photocurrent generation, photochromism of viologen and catalytic degradation of methyl orange

Multiporphyrin arrays were assembled on the surface of MWNTs to produce light-sensitive nano-composites with improved opto-electric conversion efficiency, photochromic, and photocatalytic performance.