The Cyclic Hydrogen‐Bonded 6‐Azaindole Trimer and its Prominent Excited‐State Triple‐Proton‐Transfer Reaction

Abstract

The compound 6-azaindole undergoes self-assembly by formation of N(1)ÀH···N(6) hydrogen bonds (H bonds), forming ac yclic, triply H-bonded trimer.T he formation phenomenon is visualizedb ys canning tunneling microscopy. Remarkably,t he H-bonded trimer undergoes excited-state triple proton transfer (ESTPT), resulting in ap roton-transfer tautomer emission maximized at 435 nm (325 nm of the normal emission) in cyclohexane.C omputational approaches affirm the thermodynamically favorable H-bonded trimer formation and the associated ESTPT reaction. Thus,n early half ac entury after Michael Kasha discovered the double H-bonded dimer of 7-azaindole and its associated excited-state double-proton-transfer reaction, the triply H-bonded trimer formation of 6-azaindole and its ESTPT reaction are demonstrated.[ + + ]T hese authors contributed equally to this work.Supportinginformation, includinge xperimental details, spectroscopic and dynamic measurements, computational approaches, and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.