Gianluca Azzellini - Academia.edu (original) (raw)
Papers by Gianluca Azzellini
Foram sintetizadas duas novas classes de porfirinas aquosolúveis pela quaternização dos resíduos ... more Foram sintetizadas duas novas classes de porfirinas aquosolúveis pela quaternização dos resíduos piridínicos da TPyP empregando halelos de benzila e alila. Os produtos dessas reações de quaternização TBzPyP e TAlPyP. são mais facilmenle obtidos que a TMPyP, exingindo menores tempos de reação e menores quantidades de agente alquilante para que a quaternização total da TPyP seja efetuada. Esse procedimento surge como uma rota alternativa para a obtenção de porfirinas aquosolúvei s e vale-se da alta estabilidade dos cátions benzílicos e alílicos. Os respectivos complexos de zinco e paládio foram obtidos da reação de quaternização de ZnTPyP e PdTPyP ou por reações de metalação de TBzPyP e TAlPyP. As bases livres e os metalocomplexos foram estudados quanto às suas propriedades espectroscópicas, eletroquímicas e fotoquímicas. Os novos derivados apresentam deslocamentos batocrômicos das posições dos máximos de absorção e emissão se comparados com a série metil-piridil substituída, indicand...
Program and Abstracts, 2002
Biophysical Chemistry, 1992
Optical absorplion and fluorescence spectruscopies were employed in the study of the interaction ... more Optical absorplion and fluorescence spectruscopies were employed in the study of the interaction between synthetic I.-dopa (dihydroxyphenylalanine) melanin and the cationic porphyrins tetrakis(4WmethyIpyridyl) porphyrin (TMPyP), tetrakis(4-N-benzylpyridyl)porphyrin (TBzPy?), zinc tetrakis(4-iV-methylpyridyl)porphyrin (ZnTMPyP) and zinc tetrakis (4-N-benzylpyridyl)porphyrin (ZnTBzPyP). Optical absorption and fluorescence properties of the porphyrins were dependent on the symmetry ol tbc central ring. No evidence was found for dimerization of the porphyrins in phosphate buffer, pH 7, in the concentration r;u~yc: bct+.vccn 4 S lO-H to 5 x 10ms Ad. Addition of I_-dopa melanin red shifted the optical absorption spectra of porphyrins, concomil:lW to broadening and reduction in intensity of the bands. r.-Dopa melanin also strongly quenched the fluorescence of the porphyrins. Time resolution of the fluorescence decay of porphyrins showed at least two lifetimes that were only slightly modified in the presence of melanin. The interaction between mti!tinin anu porphyrin resulted in the formation of non-fluorescent ground state complexes. It was found that there are two different classes of binding sites in melanin for complexation with cationic porphyrins and the values of dissociation constants arc of the order of 10-H M. These values and the number of binding sites arc dependent on the nature of the porphyrins. It was shown that the binding has electrostatic origin, but it is also affected by metal coordination and hydrophobic interaction.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Program and Abstracts, 2006
Phthalocyanines (Pc’s) are specially well-suited building blocks for the preparation of a wide va... more Phthalocyanines (Pc’s) are specially well-suited building blocks for the preparation of a wide variety of materials with useful properties ranging from nonlinear optical applications to photoconductors or therapeutic agents. These properties may be modulated by means of a wise selection of the central atom and/or the substituents. Among Pc's, the silicon ones are of great interest because of the possibility of axial substitution precluding aggregation in solution, and therefore, they could demonstrate appealing phenomena. Thus, substituents like dendritic structures, ferrocene, tetrathiafulvalene, carotenoids, among others, have been axially attached. Here we report the synthesis, electrochemistry and the study of the isomerization of the silicon Pc-modulated azo-based photoswitch 1. Compound 1 is the first example of a silicon Pc-azobenzene conjugate and, unlike other Pc-conjugate systems, the properties of both moieties in 1, Pc and azoarene, can be mutually modulated by light...
Modern Research in Catalysis, 2013
Metalloporphyrins immobilized into NaY zeolite are described as catalysts for hydrocarbon oxyfunt... more Metalloporphyrins immobilized into NaY zeolite are described as catalysts for hydrocarbon oxyfuntionalization. Manganese(III) and iron(III)tetrakis(4-N-methylpyridyl)-porphyrin (MnP1 and FeP1), and manganese(III) and iron(III) tetrakis(4-N-benzylpiridil)-porphyrin (MnP2 and FeP2) were impregnated (MnP1-NaY imp , FeP1-NaY imp , MnP2-NaY imp , FeP2-NaY imp , respectively) and encapsulated (MnP1-NaY, FeP1-NaY, MnP2-NaY and FeP2-NaY) into the NaY zeolite. These catalysts were used in the oxidation of (Z)-cyclooctene, cyclohexane, and adamantane by iodosylbezene (PhIO). These systems were able to epoxidize (Z)-cyclooctene with cis-epoxycyclooctane yields as high as 100%. By using cyclohexane and adamantane as substrate, the susceptibility of the benzyl groups on the porphyrin ring of the MnP materials, led to a different distribution of the oxidized products. With FePs, this susceptibility was not detected because the species responsible for the oxidations, Fe IV (O)P •+ , is more active than Mn V (O)P. In conclusion, cationic metalloporphyrins immobilized into NaX zeolites, are good cytochrome P-450 models is less polar solvents since the selectivity of the system indicates the "in cage" solvent oxygen rebound oxidative process.
Talanta, 2002
The present work describes an alternative technique for monitoring the rate of oxygen consumption... more The present work describes an alternative technique for monitoring the rate of oxygen consumption during the oxidation of HSO(3)(-) catalyzed by manganese and iron ions. The method is based on the spectrofluorimetric monitoring of the quenching effect of molecular oxygen on the emission of the photoexcited [Ru(bipy)(3)](2+) ion, added to the reaction mixtures. The effects of Fe(III), at very low concentrations, and of Mn(II) on the oxidation of HSO(3)(-) by dissolved oxygen, have been investigated. The metal ions in the trivalent oxidation state react with HSO(3)(-) to initiate a radical chain reaction in which HSO(3)(-) is oxidized to sulfate and the metal ion is reduced to the divalent state. The synergistic effect of Mn(II) and Fe(III) was clearly evaluated. Possible parallel reactions with the oxygen indicator, [Ru(bipy)(3)](2+), are considered.
Pigment Cell Research, 1993
Electron Paramagnetic Resonance (EPR) spectroscopy was employed in the study of the interaction b... more Electron Paramagnetic Resonance (EPR) spectroscopy was employed in the study of the interaction between L-3,4-dihydroxyphenylalanine (L-Dopa) melanin and the cationic porphyrins meso-tetrakis(1-methylpyridinium-4yl)-porphyrin (TMPyP), meso-tetrakis-(1-benzylpyridinium-4-yl)-porphyrin (TBzPyP), and their respectives complexes ZnTMPyP and ZnTBzPyP. By monitoring signal intensities and progressive microwave power saturation it was shown that the interaction increases the equilibrium concentration of free radicals in L-Dopa melanin in the dark. The extent of increase is dependent on the presence of molecular oxygen and on the type of porphyrin. Not all interacting sites available for complexation in L-Dopa melanin are involved in the formation of free radicals. It was also observed that the interaction with porphyrins promotes an increase in the number of photoinduced free radicals in L-Dopa melanin during illumination with visible light.
Journal of the Brazilian Chemical Society, 2003
![Research paper thumbnail of Dendrimers with a Photoactive and Redox-Active [Ru(bpy)3]2+-Type Core: Photophysical Properties, Electrochemical Behavior, and Excited-State Electron-Transfer Reactions](https://attachments.academia-assets.com/93846502/thumbnails/1.jpg)
](Journal of the American Chemical Society, 1999
We report the synthesis of six new dendrimers built around a [Ru(bpy) 3 ] 2+-type core (bpy) 2,2′... more We report the synthesis of six new dendrimers built around a [Ru(bpy) 3 ] 2+-type core (bpy) 2,2′bipyridine) and bearing up to 24 4′-tert-butylphenyloxy or 48 benzyl units in the periphery. The metallodendrimers were obtained by complexation of ruthenium trichloride or Ru(bpy) 2 Cl 2 with bipyridine ligands carrying dendritic wedges in the 4,4′-positions. The absorption spectra and luminescence properties (spectra and lifetimes at 77 and 298 K; quantum yields at 298 K) of the six novel compounds are reported. All of them show the characteristic luminescence of the [Ru(bpy) 3 ] 2+-type core unit. The dendritic branches protect the luminescent excited state of the core by dioxygen quenching. For the three compounds containing the 4′-tert-butylphenyloxy peripheral units, the electrochemical behavior and the excited-state quenching via electron transfer were also studied. The electrochemical experiments have evidenced an oxidation and three reduction one-electron processes centered in the [Ru(bpy) 3 ] 2+-type core and two multielectron oxidation processes involving the dioxybenzeneand oxybenzene-type units of the dendritic branches. The core of the largest dendrimer shows an electrochemical behavior typical of encapsulated electroactive units. The reaction of the luminescent excited state of the [Ru-(bpy) 3 ] 2+-type core with three electron-transfer quenchers (namely, methyl viologen dication, tetrathiafulvalene, and anthraquinone-2,6-disulfonate anion) was found to take place by a dynamic mechanism in all cases. The quenching rate constants, obtained by Stern-Volmer kinetic analysis, are compared with those found for the simple [Ru(bpy) 3 ] 2+ complex. The results show that, for each quencher, the value of the rate constant decreases with increasing number and size of the dendritic branches. For the second-generation dendrimer containing 24 4′-tert-butylphenyloxy units at the periphery, the rate constant of the reaction with methyl viologen is more than 1 order of magnitude smaller than that of the "naked" [Ru(bpy) 3 ] 2+ complex. All the experiments were performed in acetonitrile solution, except for luminescence experiments at 77 K where butyronitrile was used.
Journal of the American Chemical Society, 1998
Two poly(propyleneimine) dendrimers bearing up to 32 photoisomerizable azobenzene groups in the p... more Two poly(propyleneimine) dendrimers bearing up to 32 photoisomerizable azobenzene groups in the periphery have been used as potential hosts for eosin Y (2′,4′,5′,7′-tetrabromofluorescein dianion). The all-E azobenzene dendrimers can be reversibly switched to their Z form by light excitation. Both the E and Z forms of the dendrimers quench the eosin fluorescence by a static mechanism. The quenching is most likely due to an electron-transfer reaction between the singlet excited state of eosin and the tertiary amine units present along the branches of the dendrimers. Quenching by the Z form of the dendrimers is more efficient than quenching by the E form. The E f Z and Z f E photoisomerization reactions of the azobenzene units of the dendrimers are sensitized by eosin via a triplet-triplet energy transfer mechanism. The results obtained indicate that eosin is hosted by the dendrimers and suggest that the Z forms are more efficient hosts than the E forms.
Inorganica Chimica Acta, 2009
The heteroaggregation behavior between a new class of nonplanar cationic b-octabrominated meso-al... more The heteroaggregation behavior between a new class of nonplanar cationic b-octabrominated meso-alkylpyridinium zinc(II)-porphyrins (b-Br 8 (ZnP)) and anionic tetrasulfonated metallophthalocyanines (MTSPc, M = Ni(II) and Cu(II)) has been studied by UV-Vis electronic spectroscopy, in dimethylsulfoxide (DMSO) solution. The heteroaggregate stoichiometry and the association constants were determined by means of Job plots. Dimers and unexpected trimers, taking into account the existence of axially coordinated DMSO molecules to the central metal in both b-Br 8 (ZnP) and MTSPc complexes, are formed in solution. The spectroscopic properties of the heteroaggregates are markedly different from those observed in the correspondent planar cationic derivatives, the heteroaggregates showing major changes predominantly in the b-Br 8 (ZnP) Soret band region and minor effects in the MTSPc Q bands. The observed changes in the Soret band region (red/blue shifts, decrease in the absorption intensities) depend on the nature of the alkyl substituent attached to the meso-pyridinium group. The greater versatility of the nonplanar porphyrins accommodating the meso-substituents in out-of-plane and in-plane conformations is proposed to explain the observed stoichiometries and the differences on the heteroaggregates spectroscopic properties for each b-Br 8 ZnP compound. The likely conformations assumed by the meso-substituents in these b-Br 8 (ZnP) compounds and its spectroscopic characteristics are in accordance with the participation of the substituents as the main factor on the extent of the observed red-shifted spectra in nonplanar porphyrins. The obtained association constants (K IP) for the dimers and trimers are lower than those previously found for the similar planar cationic porphyrin systems, due to the lack of extensive p-p interactions and to the less effective approximation between the ionic groups, resulting in loosened heteroaggregates, particularly for the trimeric systems. Furthermore, the experimental results suggest that the NiTSPc is more distorted in DMSO solution than the CuTSPc derivative, favoring the interaction with the nonplanar b-Br 8 (ZnP) compounds.
Chemistry - A European Journal, 1998
Azobenzene-Functionalized Cascade Molecules: Photoswitchable Supramolecular Systems ... Isomeriza... more Azobenzene-Functionalized Cascade Molecules: Photoswitchable Supramolecular Systems ... Isomerization of azobenzene involves a large structural rearrangement. ...
Foram sintetizadas duas novas classes de porfirinas aquosolúveis pela quaternização dos resíduos ... more Foram sintetizadas duas novas classes de porfirinas aquosolúveis pela quaternização dos resíduos piridínicos da TPyP empregando halelos de benzila e alila. Os produtos dessas reações de quaternização TBzPyP e TAlPyP. são mais facilmenle obtidos que a TMPyP, exingindo menores tempos de reação e menores quantidades de agente alquilante para que a quaternização total da TPyP seja efetuada. Esse procedimento surge como uma rota alternativa para a obtenção de porfirinas aquosolúvei s e vale-se da alta estabilidade dos cátions benzílicos e alílicos. Os respectivos complexos de zinco e paládio foram obtidos da reação de quaternização de ZnTPyP e PdTPyP ou por reações de metalação de TBzPyP e TAlPyP. As bases livres e os metalocomplexos foram estudados quanto às suas propriedades espectroscópicas, eletroquímicas e fotoquímicas. Os novos derivados apresentam deslocamentos batocrômicos das posições dos máximos de absorção e emissão se comparados com a série metil-piridil substituída, indicand...
Program and Abstracts, 2002
Biophysical Chemistry, 1992
Optical absorplion and fluorescence spectruscopies were employed in the study of the interaction ... more Optical absorplion and fluorescence spectruscopies were employed in the study of the interaction between synthetic I.-dopa (dihydroxyphenylalanine) melanin and the cationic porphyrins tetrakis(4WmethyIpyridyl) porphyrin (TMPyP), tetrakis(4-N-benzylpyridyl)porphyrin (TBzPy?), zinc tetrakis(4-iV-methylpyridyl)porphyrin (ZnTMPyP) and zinc tetrakis (4-N-benzylpyridyl)porphyrin (ZnTBzPyP). Optical absorption and fluorescence properties of the porphyrins were dependent on the symmetry ol tbc central ring. No evidence was found for dimerization of the porphyrins in phosphate buffer, pH 7, in the concentration r;u~yc: bct+.vccn 4 S lO-H to 5 x 10ms Ad. Addition of I_-dopa melanin red shifted the optical absorption spectra of porphyrins, concomil:lW to broadening and reduction in intensity of the bands. r.-Dopa melanin also strongly quenched the fluorescence of the porphyrins. Time resolution of the fluorescence decay of porphyrins showed at least two lifetimes that were only slightly modified in the presence of melanin. The interaction between mti!tinin anu porphyrin resulted in the formation of non-fluorescent ground state complexes. It was found that there are two different classes of binding sites in melanin for complexation with cationic porphyrins and the values of dissociation constants arc of the order of 10-H M. These values and the number of binding sites arc dependent on the nature of the porphyrins. It was shown that the binding has electrostatic origin, but it is also affected by metal coordination and hydrophobic interaction.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Program and Abstracts, 2006
Phthalocyanines (Pc’s) are specially well-suited building blocks for the preparation of a wide va... more Phthalocyanines (Pc’s) are specially well-suited building blocks for the preparation of a wide variety of materials with useful properties ranging from nonlinear optical applications to photoconductors or therapeutic agents. These properties may be modulated by means of a wise selection of the central atom and/or the substituents. Among Pc's, the silicon ones are of great interest because of the possibility of axial substitution precluding aggregation in solution, and therefore, they could demonstrate appealing phenomena. Thus, substituents like dendritic structures, ferrocene, tetrathiafulvalene, carotenoids, among others, have been axially attached. Here we report the synthesis, electrochemistry and the study of the isomerization of the silicon Pc-modulated azo-based photoswitch 1. Compound 1 is the first example of a silicon Pc-azobenzene conjugate and, unlike other Pc-conjugate systems, the properties of both moieties in 1, Pc and azoarene, can be mutually modulated by light...
Modern Research in Catalysis, 2013
Metalloporphyrins immobilized into NaY zeolite are described as catalysts for hydrocarbon oxyfunt... more Metalloporphyrins immobilized into NaY zeolite are described as catalysts for hydrocarbon oxyfuntionalization. Manganese(III) and iron(III)tetrakis(4-N-methylpyridyl)-porphyrin (MnP1 and FeP1), and manganese(III) and iron(III) tetrakis(4-N-benzylpiridil)-porphyrin (MnP2 and FeP2) were impregnated (MnP1-NaY imp , FeP1-NaY imp , MnP2-NaY imp , FeP2-NaY imp , respectively) and encapsulated (MnP1-NaY, FeP1-NaY, MnP2-NaY and FeP2-NaY) into the NaY zeolite. These catalysts were used in the oxidation of (Z)-cyclooctene, cyclohexane, and adamantane by iodosylbezene (PhIO). These systems were able to epoxidize (Z)-cyclooctene with cis-epoxycyclooctane yields as high as 100%. By using cyclohexane and adamantane as substrate, the susceptibility of the benzyl groups on the porphyrin ring of the MnP materials, led to a different distribution of the oxidized products. With FePs, this susceptibility was not detected because the species responsible for the oxidations, Fe IV (O)P •+ , is more active than Mn V (O)P. In conclusion, cationic metalloporphyrins immobilized into NaX zeolites, are good cytochrome P-450 models is less polar solvents since the selectivity of the system indicates the "in cage" solvent oxygen rebound oxidative process.
Talanta, 2002
The present work describes an alternative technique for monitoring the rate of oxygen consumption... more The present work describes an alternative technique for monitoring the rate of oxygen consumption during the oxidation of HSO(3)(-) catalyzed by manganese and iron ions. The method is based on the spectrofluorimetric monitoring of the quenching effect of molecular oxygen on the emission of the photoexcited [Ru(bipy)(3)](2+) ion, added to the reaction mixtures. The effects of Fe(III), at very low concentrations, and of Mn(II) on the oxidation of HSO(3)(-) by dissolved oxygen, have been investigated. The metal ions in the trivalent oxidation state react with HSO(3)(-) to initiate a radical chain reaction in which HSO(3)(-) is oxidized to sulfate and the metal ion is reduced to the divalent state. The synergistic effect of Mn(II) and Fe(III) was clearly evaluated. Possible parallel reactions with the oxygen indicator, [Ru(bipy)(3)](2+), are considered.
Pigment Cell Research, 1993
Electron Paramagnetic Resonance (EPR) spectroscopy was employed in the study of the interaction b... more Electron Paramagnetic Resonance (EPR) spectroscopy was employed in the study of the interaction between L-3,4-dihydroxyphenylalanine (L-Dopa) melanin and the cationic porphyrins meso-tetrakis(1-methylpyridinium-4yl)-porphyrin (TMPyP), meso-tetrakis-(1-benzylpyridinium-4-yl)-porphyrin (TBzPyP), and their respectives complexes ZnTMPyP and ZnTBzPyP. By monitoring signal intensities and progressive microwave power saturation it was shown that the interaction increases the equilibrium concentration of free radicals in L-Dopa melanin in the dark. The extent of increase is dependent on the presence of molecular oxygen and on the type of porphyrin. Not all interacting sites available for complexation in L-Dopa melanin are involved in the formation of free radicals. It was also observed that the interaction with porphyrins promotes an increase in the number of photoinduced free radicals in L-Dopa melanin during illumination with visible light.
Journal of the Brazilian Chemical Society, 2003
Journal of the American Chemical Society, 1999
We report the synthesis of six new dendrimers built around a [Ru(bpy) 3 ] 2+-type core (bpy) 2,2′... more We report the synthesis of six new dendrimers built around a [Ru(bpy) 3 ] 2+-type core (bpy) 2,2′bipyridine) and bearing up to 24 4′-tert-butylphenyloxy or 48 benzyl units in the periphery. The metallodendrimers were obtained by complexation of ruthenium trichloride or Ru(bpy) 2 Cl 2 with bipyridine ligands carrying dendritic wedges in the 4,4′-positions. The absorption spectra and luminescence properties (spectra and lifetimes at 77 and 298 K; quantum yields at 298 K) of the six novel compounds are reported. All of them show the characteristic luminescence of the [Ru(bpy) 3 ] 2+-type core unit. The dendritic branches protect the luminescent excited state of the core by dioxygen quenching. For the three compounds containing the 4′-tert-butylphenyloxy peripheral units, the electrochemical behavior and the excited-state quenching via electron transfer were also studied. The electrochemical experiments have evidenced an oxidation and three reduction one-electron processes centered in the [Ru(bpy) 3 ] 2+-type core and two multielectron oxidation processes involving the dioxybenzeneand oxybenzene-type units of the dendritic branches. The core of the largest dendrimer shows an electrochemical behavior typical of encapsulated electroactive units. The reaction of the luminescent excited state of the [Ru-(bpy) 3 ] 2+-type core with three electron-transfer quenchers (namely, methyl viologen dication, tetrathiafulvalene, and anthraquinone-2,6-disulfonate anion) was found to take place by a dynamic mechanism in all cases. The quenching rate constants, obtained by Stern-Volmer kinetic analysis, are compared with those found for the simple [Ru(bpy) 3 ] 2+ complex. The results show that, for each quencher, the value of the rate constant decreases with increasing number and size of the dendritic branches. For the second-generation dendrimer containing 24 4′-tert-butylphenyloxy units at the periphery, the rate constant of the reaction with methyl viologen is more than 1 order of magnitude smaller than that of the "naked" [Ru(bpy) 3 ] 2+ complex. All the experiments were performed in acetonitrile solution, except for luminescence experiments at 77 K where butyronitrile was used.
Journal of the American Chemical Society, 1998
Two poly(propyleneimine) dendrimers bearing up to 32 photoisomerizable azobenzene groups in the p... more Two poly(propyleneimine) dendrimers bearing up to 32 photoisomerizable azobenzene groups in the periphery have been used as potential hosts for eosin Y (2′,4′,5′,7′-tetrabromofluorescein dianion). The all-E azobenzene dendrimers can be reversibly switched to their Z form by light excitation. Both the E and Z forms of the dendrimers quench the eosin fluorescence by a static mechanism. The quenching is most likely due to an electron-transfer reaction between the singlet excited state of eosin and the tertiary amine units present along the branches of the dendrimers. Quenching by the Z form of the dendrimers is more efficient than quenching by the E form. The E f Z and Z f E photoisomerization reactions of the azobenzene units of the dendrimers are sensitized by eosin via a triplet-triplet energy transfer mechanism. The results obtained indicate that eosin is hosted by the dendrimers and suggest that the Z forms are more efficient hosts than the E forms.
Inorganica Chimica Acta, 2009
The heteroaggregation behavior between a new class of nonplanar cationic b-octabrominated meso-al... more The heteroaggregation behavior between a new class of nonplanar cationic b-octabrominated meso-alkylpyridinium zinc(II)-porphyrins (b-Br 8 (ZnP)) and anionic tetrasulfonated metallophthalocyanines (MTSPc, M = Ni(II) and Cu(II)) has been studied by UV-Vis electronic spectroscopy, in dimethylsulfoxide (DMSO) solution. The heteroaggregate stoichiometry and the association constants were determined by means of Job plots. Dimers and unexpected trimers, taking into account the existence of axially coordinated DMSO molecules to the central metal in both b-Br 8 (ZnP) and MTSPc complexes, are formed in solution. The spectroscopic properties of the heteroaggregates are markedly different from those observed in the correspondent planar cationic derivatives, the heteroaggregates showing major changes predominantly in the b-Br 8 (ZnP) Soret band region and minor effects in the MTSPc Q bands. The observed changes in the Soret band region (red/blue shifts, decrease in the absorption intensities) depend on the nature of the alkyl substituent attached to the meso-pyridinium group. The greater versatility of the nonplanar porphyrins accommodating the meso-substituents in out-of-plane and in-plane conformations is proposed to explain the observed stoichiometries and the differences on the heteroaggregates spectroscopic properties for each b-Br 8 ZnP compound. The likely conformations assumed by the meso-substituents in these b-Br 8 (ZnP) compounds and its spectroscopic characteristics are in accordance with the participation of the substituents as the main factor on the extent of the observed red-shifted spectra in nonplanar porphyrins. The obtained association constants (K IP) for the dimers and trimers are lower than those previously found for the similar planar cationic porphyrin systems, due to the lack of extensive p-p interactions and to the less effective approximation between the ionic groups, resulting in loosened heteroaggregates, particularly for the trimeric systems. Furthermore, the experimental results suggest that the NiTSPc is more distorted in DMSO solution than the CuTSPc derivative, favoring the interaction with the nonplanar b-Br 8 (ZnP) compounds.
Chemistry - A European Journal, 1998
Azobenzene-Functionalized Cascade Molecules: Photoswitchable Supramolecular Systems ... Isomeriza... more Azobenzene-Functionalized Cascade Molecules: Photoswitchable Supramolecular Systems ... Isomerization of azobenzene involves a large structural rearrangement. ...