2-(2′-Pyridyl)benzimidazole as a Fluorescent Probe of Hydration of Nafion Membranes

Abstract

2,2'-(Pyridyl)benzimidazole is used as a probe to explore proton transfer through nafion membranes. The probe marks the availability of water in native as well as cation-exchanged membrane. Using steady state and time-resolved fluorescence studies, it has been shown that the rotation of the pyridyl and benzimidazole rings with respect to each other, which is ultrafast in higher water contents, is hindered as the water content in the membranes is decreased. In cation-exchanged membranes, it is observed that the formation of the ESPT (excited state proton transfer) state is reduced to a large extent. Thus, it may be inferred that the proton transport is observed to be hindered even in molecular dimensions of one water molecule thereby bolstering the contention that it may not be essential for water channels to break for proton conductivity to decrease.

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

“…The anomalous emission at 435 nm, observed immediately after excitation, is ascribed to this conformationally strained geometry of the tautomer. Similar observations have been reported for 2PBI in Nafion membrane . Upon conformational relaxation, T* with coplanar rings, can be formed.…”

“…The reason for this assignment is that the time‐resolved fluorescence spectra at longer times have maxima at the same position (460–470 nm) (Figure a) as the steady‐state emission spectra of 4PBI in hydrated films, in which conformationally relaxed T* is expected to occur. Such conformational relaxation is slow at low hydration levels . At high hydration levels, the rotation around the two rings can be expected to be very fast; therefore, the fluorescence decays are independent of wavelength of emission and emission band is redshifted.…”

Enhancing NMR Sensitivity of Natural‐Abundance Low‐γ Nuclei by Ultrafast Magic‐Angle‐Spinning Solid‐State NMR Spectroscopy

“…The reason for this assignment is that the time-resolvedf luorescencespectra at longert imes have maxima at the same position (460-470 nm) ( Figure 5a)a st he steady-state emission spectra of 4PBI in hydrated films, in which conformationally relaxed T* is expectedt oo ccur.S uch conformationalr elaxation is slow at low hydration levels. [41] At high hydration levels, the rotation aroundt he two rings can be expected to be very fast;t here-fore, the fluorescenced ecaysa re independent of wavelength of emission and emission band is redshifted.…”

“…The anomalouse mission at 435 nm, observed immediately after excitation, is ascribed to this conformationallys trained geometry of the tautomer.S imilar observations have been reported for 2PBI in Nafion membrane. [41] Upon conformational relaxation, T* with coplanar rings,c an be formed. The reason for this assignment is that the time-resolvedf luorescencespectra at longert imes have maxima at the same position (460-470 nm) ( Figure 5a)a st he steady-state emission spectra of 4PBI in hydrated films, in which conformationally relaxed T* is expectedt oo ccur.S uch conformationalr elaxation is slow at low hydration levels.…”

Synthesis Crystal Structure and Properties of Iodide, Hexafluoro- phosphate and Bis(trifluoromethane sulfonamide) Salts of 1-Ferrocenyl Methyl-2-ferrocenyl-3-alklybenzimidazolium

“…研究表明, 该类化合物对高氯酸铵的热分解具有较 好的催化性能. 苯并咪唑类化合物具有生物活性及结构 易修饰性, 其广泛应用于药物开发 [13] 、离子液体的合 成 [14] 、有机光电功能分子 [15] 、金属配合物的合成 [16] 、离 子识别主体分子的合成 [17] 氧气的含量, 及体系的 pH 值都能影响反应主产物的形 成. 3-位置引入的官能团的空间位阻大小及产物中阴离子 的类型对产物在电化学曲线中的峰电位无明显的影响.…”