Evidence of porphyrin monoanion by simple spectrophotometric titration in dimethyl sulfoxide

Abstract

We present a simple spectrophotometric titration to illustrate the existence of stable porphyrin monoanion in dimethyl sulfoxide by tetrabutylammonium hydroxide towards justifying the term 'free-acid porphyrin' for metal-free porphyrin.

Deprotonation‐Induced Aromaticity Enhancement and New Conjugated Networks in meso‐Hexakis(pentafluorophenyl)[26]hexaphyrin

“…[11] Herein, as a part of our continuous efforts to explore novel electronic states of expanded porphyrins, we propose a new method for controlling the aromaticity of neutral [26]hexaphyrin by deprotonation with tetrabutylammonium fluoride (TBAF). In the excited states of porphyrins, inner NH tautomerism has been identified to play an important role in radiationless decays, and thus, deuterium exchange [12] and deprotonation experiments [13] have been conducted to reveal the influence of NH tautomerism on excited-state decay.…”

Excited-State Quenching of Porphyrins by Hydrogen-Bonded Phenol-Pyridine Pair: Evidence of Proton-Coupled Electron Transfer

“…However, interaction at core sites of the porphyrin macrocycle brings a split in the Soret band with a peak at around 450 nm. 58,59 As shown in the figure, addition of 5 M TMPy in the solution brings a little change in the Soret band with a small red shift of the peak. This suggests that even such high concentration of TMPy does not interact or very weakly interact with the N−H group of pyrrole.…”

“…Hence, in comparison to the earlier observation by Guo et al about two-stage deprotonation (first peripheral phenolic-H then inner core pyrrolic-H) of (4,0)­TPP, we affirm that, in lower additive concentration, interaction (H-bonding) occurs at peripheral sites; in the studied systems, it is the OH group of phenol, while it occurs at the inner core site at very higher concentration of respective additives. However, interaction at core sites of the porphyrin macrocycle brings a split in the Soret band with a peak at around 450 nm. , As shown in the figure, addition of 5 M TMPy in the solution brings a little change in the Soret band with a small red shift of the peak. This suggests that even such high concentration of TMPy does not interact or very weakly interact with the N–H group of pyrrole.…”

“…The photophysical properties of the porphyrins are generally manipulated by peripheral or central substitutions, which lead to charge movement in or out of the macrocycle. Substitutions on the phenyl ring of the tetraphenylporphyrins (TPP) resulted in the change in the shape of absorption spectra depending upon the extent of resonative interactions between porphyrin macrocycle and peripheral substitutions. − In a basic solution, quinonoid resonance structures comprising charge transfer were observed in (4,0)­TPP . Notably, (4,0)­TPP is a class of TPP-based molecules whose sensitive and specific response to peripheral H-bonding to the H atom of the −OH group of phenol with bases occurs prior to the H atom of inner core pyrrole, and this makes (4,0)­TPP and other derivatives useful candidates in exploring the role of H-bonding in electron transfer events.…”