Role of intramolecular hydrogen bonding in the excited-state intramolecular double proton transfer (ESIDPT) of calix[4]arene: A TDDFT study

Abstract

Abstract:The time-dependent density functional theory (TDDFT) method was performed to investigate the excitedstate intramolecular double proton transfer (ESIDPT) reaction of calix [4]arene (C4A) and the role of the intramolecular hydrogen bonds in the ESIDPT process. The geometries of C4A in the ground state and excited states (S 1 , S 2 and T 1 ) were optimized. Four intramolecular hydrogen bonds formed in the C4A are strengthened or weakened in the S 2 and T 1 states compared to those in the ground state. Interestingly, upon excitation to the S 1 state of C4A, two protons H1 and H2 transfer along the two intramolecular hydrogen bonds O1-H1· · · O2 and O2-H2· · · O3, while the other two protons do not transfer. The ESIDPT reaction breaks the primary symmetry of C4A in the ground state. The potential energy curves of proton transfer demonstrate that the ESIDPT process follows the stepwise mechanism but not the concerted mechanism. Findings indicate that intramolecular hydrogen bonding is critical to the ESIDPT reactions in intramolecular hydrogen-bonded systems.

Supramolecular Calix[n]arenes-Intercalated Graphene Oxide Membranes for Efficient Proton Conduction

“…The enhancement of proton conductivity under low RH was attributed to the reasons below: (i) the high density of sulfonic acid groups of SC­[ n ]­A (5.37 mmol g –1 ) favored the construction of well-connected channels for proton transfer even under low humidity; and (ii) the phenolic hydroxyl groups along the lower edge were able to form intramolecular hydrogen bonds. When a proton left, the oxygen anion could be stable due to the special structure of the SC­[ n ]­A and the generation of intramolecular H-bonding conjugate effect, and then other protons nearby would hop to this site easily, which was different from small molecules, promoting the proton hopping between SC­[ n ]­A, according to the Grotthuss mechanism …”