Structural Effects of the β-Vinyl Linker in Pyridinium Porphyrins: Spectroscopic Studies in Organic Solvents and AOT Reverse Micelles

Abstract

Two isomeric β-vinylpyridinium porphyrins, 2-[2-(2-methylpyridinium)vinyl]-5,10,15,20-tetraphenylporphyrin (1, ortho isomer) and 2-[2-(4-methylpyridinium)vinyl]-5,10,15,20-tetraphenylporphyrin (2, para isomer), which have shown different photodynamic behavior were investigated in organic solvents and sodium 1,4-bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles. In organic systems, the absorption spectra present a red-shifted band that is more intense in the para isomer, in addition to the usual Soret band. This new band presents interesting solvatochromic effects which obey the multiparametric Kamlet-Taft equation. In AOT reverse micelles, the ortho isomer exhibits a strong dependence with the parameter ω0 = [H2O]/[AOT] which indicates that the molecule resides at the interface toward the organic phase. By contrast, no evidence was detected for the encapsulation of para isomer 2 in AOT reverse micelles. The hypothesis of two ground state isomers with different contributions of trans and quinoid structures is advanced on the basis of the overall data collected from electronic absorption, steady-state, and transient-state fluorescence emission. A charge transfer state in which an electron is fully transferred from the porphyrin to the pyridinium moiety is associated to a quinoid structure in isomer 2. The trans/quinoid relative proportions may be accounted for by the orientation of the ortho-/para-pyridinium isomers relatively to the porphyrin core.

Synthesis, spectroscopic, electrochemical redox, solvatochromism and anion binding properties of β-tetra- and -octaphenylethynyl substitutedmeso-tetraphenylporphyrins

“…† The Soret band of H 2 TPP(PE) 8 in various solvents lies between 506 and 524 nm and is seen to have red-shi with increasing solvent polarity. This positive solvatochromism [17][18][19] is ascribed to the possibility of charge transfer between the electron rich porphyrin core and the electron decient peripheral PE groups. Notably, the b-phenylethynyl substituted porphyrins have been shown to exhibit charge transfer characteristics.…”

“…These results suggests an internal charge transfer which results from stabilization of polar excited state by polar solvents and is well documented with donor-acceptor uorophores. [17][18][19]21 H 2 TPP(PE) 8 exhibited blue shied emission (negative solvatochromism) in DMF. This is possibly due to less stable and less polar excited state than the ground state which is further supported by the lower life time (0.66 ns) as compared to other solvents such as CH 2 Cl 2 , toluene, THF and dioxane (life time 1.3 to 1.6 ns) (Table S4, ESI †).…”

“…This is possibly due to less stable and less polar excited state than the ground state which is further supported by the lower life time (0.66 ns) as compared to other solvents such as CH 2 Cl 2 , toluene, THF and dioxane (life time 1.3 to 1.6 ns) (Table S4, ESI †). 17 To investigate further solvatochromism behaviour of PE groups, we recorded the uorescence life time decay and analysed using a multi exponential decay. In more polar solvents, H 2 TPP(PE) 8 and ZnTPP(PE) 8 exhibited di-or triexponential uorescence decay, this is may be due to the emission of porphyrin core is partially quenched by the acceptor PE moieties.…”

β-Formyl- and β-Vinylporphyrins: Magic Building Blocks for Novel Porphyrin Derivatives

“…It was also found that the different gas phase behaviour is less effective when the corresponding zinc(II) complexes were studied. The structural effects of the β-vinyl linker in the electronic properties of isomeric pyridinium porphyrins 16a and 16b were accessed later by steady state and transient spectroscopies both in organic solvents and in AOT reverse micelles, the biomimetic models of natural membranes [ 102 ]. Different contributions of the trans and quinoid resonance structures in the ground state were proposed for both isomers.…”