Multiple Hydrogen Bonds Tuning Guest/Host Excited-State Proton Transfer Reaction:  Its Application in Molecular Recognition

Abstract

A molecular recognition concept exploiting multiple-hydrogen-bond fine-tuned excited-state proton-transfer (ESPT) was conveyed using 3,4,5,6-tetrahydrobis(pyrido[3,2-g]indolo)[2,3-a:3',2'-j]acridine (1a). The catalytic type 1a/carboxylic acids hydrogen-bonding (HB) complexes undergo ultrafast ESPT, resulting in an anomalously large Stokes shifted tautomer emission (lambdamax approximately 600 nm). Albeit forming a quadruple HB complex, ESPT is prohibited in the noncatalytic-type 1a/urea complexes (lambdamax approximately 430 nm). The HB configuration tuning ESPT properties lead to a feasible design for sensing multiple-HB-site analytes of biological interest.

Solvent-Dependent Ground- and Excited-State Tautomerism in 2-(6‘-Hydroxy-2‘-pyridyl)benzimidazole

“…It is well-known that the excited-state acid−base properties of molecules may differ markedly from those in the ground state, leading to proton-transfer processes in the excited state. Molecules with acid and basic functionalities may undergo an excited-state intramolecular proton transfer (ESIPT) from the acidic to the basic site, yielding a phototautomer. − Many bifunctional molecules without the geometrical requirements for an ESIPT can still undergo an excited-state proton transfer (ESPT) assisted by species with hydrogen bond accepting and donating abilities, these acting as bridges between the acid and the basic site. − The understanding of these processes is of importance in chemistry and biology, as they could help to unravel complex problems as the mechanism of proton-relay processes in biological systems, the transport of protons in water, − the mutagenesis mechanisms, − and molecular recognition …”

Towards Smart Drug Delivery: Exploration of a Molecularly Imprinted Polymer Network

“…26 Some of the weak interactions include, but are not limited to: hydrophobicity, [27][28][29] dipole-dipole, cation-π interactions, charge transfer (π-π staking), and hydrogen bonding. 30,31 Hydrogen bonds are in the energy range from 5-30 kJ/mol, weaker than ionic bonds but stronger than van der Waals forces. 15 They are attributed to the interaction of an electron cloud polarized by nuclei with the energy less than 5 kJ/mol.…”

Photoinduced coupled twisted intramolecular charge transfer and excited-state proton transfer via intermolecular hydrogen bonding: A DFT/TD-DFT study

“…Upon photoexcitation, molecules in chemistry and biology can undergo excited-state proton transfer (ESPT) associated with hydrogen bond accepting and donating abilities [13][14][15]. Specifically, it has been demonstrated that ground-state proton transfer (PT) and/or ESPT via hydrogen bonding are essential to unravel complex problems, such as the mechanism of proton-relay processes in biological systems, transport proton in water, mutagenesis and molecular recognition [16][17][18][19][20][21][22], etc. In fact, PT and ESPT can be enhanced or restrained by intermolecular and/or intramolecular hydrogen-bonding interactions [23][24][25][26][27][28][29].…”