Excited‐State Proton Transfer and Conformational Relaxation of 2‐(4′‐Pyridyl)benzimidazole in Nafion Films

Abstract

The effect of annealing on the acidity and water uptake of Nafion films has been studied by using the acidity sensing fluorophore 2-(4'-pyridyl)benzimidazole (4PBI). The difference in acidity and the microenvironment of the fluorophore in annealed and nonannealed films is brought out in this study. The annealed film is found to have less water uptake than nonannealed films. The amount of water uptake increases upon acid treatment of the films, as all the steady-state and time-resolved behaviour of the molecule in nonannealed films is restored. These observations are rationalised by the formation of anhydrides upon annealing and their hydrolysis to sulfonic acid groups upon acid treatment. Interestingly, the acidity of annealed films is found to be even less than that of Na exchanged films, indicating that annealing removes more protons from the Nafion films than cation exchange can.

Reversible pH‐Controlled Catenation of a Benzobisimidazole‐Based Tetranuclear Rectangle

“…Figure S39 illustrates the spectral variations recorded during absorption spectrophotometric titration of BBI as a function of pH, which are in agreement with reported results on 4-pyridylbenzimidazole (4PBI). [28] Under neutral pH conditions (MeOH/H 2 O 80/20 w/w, Figure S39), BBI is characterized by an intense absorption band in the UV region centered at 357 nm (ɛ 357 = 3.50 × 10 4 M À 1 cm À 1 ) in agreement with the data recorded in methanol. Increasing the pH from ~6.5 to ~11.9 induces a bathochromic shift of 23 nm of the ππ* transitions.…”

A combined experimental and computational study on the deactivation of a photo-excited 2,2′-pyridylbenzimidazole–water complex via excited-state proton transfer

“…22,23 Moreover, the PBI molecule exhibits excellent bioactivity, and the metal clusters of the PBI molecule have demonstrated applications in the field of medicinal chemistry. [24][25][26][27][28][29] The molecule is vastly studied, focusing on the tautomerization pathway in the solution phase, 22,23,[30][31][32][33] but there is no investigation of the competing excited-state processes in the isolated molecular complexes. The proximity of the pyridine N and benzimidazole N-H groups makes the molecule an excellent candidate for investigating the above processes.…”

Excited State Proton Transfer of a Versatile Fluorescent Probe in Different Reverse Micelles: An Overview

“…Since proton transfer is extremely sensitive to the structure and dynamics of the surrounding water molecules, these reactions can be used as convenient reporters of the solvent microenvironment. In fact, studies on excited state prototropic behavior of fluorescent molecules have led to a wealth of knowledge about the microenvironments in micelles, reverse micelles, biological cells, proteins, macrocyclic hosts, membrane films and other supramolecular structures (Amdursky et al, 2014;Chowdury et al, 2015;Cohen et al, 2011;Douhal et al, 2007;Gepshtein et al, 2006;Singhal et al, 2016).…”