Green Multicomponent One‐Pot Synthesis of 2‐(2′‐Hydroxyphenyl)Imidazo[1,2‐a]Pyridine Analogs with an Intramolecular Hydrogen‐Bonded Eight‐Membered Ring Exhibiting Excited‐State Intramolecular Proton Transfer Luminescence

Multicomponent reactions are excellent tools to generate complex structures with broad chemical diversity and fluorescent properties. The sonochemical multicomponent one‐pot synthesis of novel organic luminescent heterocycles, such as 2‐(2′‐hydroxyphenyl)imidazo[1,2‐a]pyridine (2‐HPIP) analogs, is described. The Groebke–Blackburn–Bienaymé reaction (GBBR) affords good to excellent yields (75–95%). Notably, the compound 4b forms an intramolecular hydrogen‐bonded eight‐membered ring (8‐MR) in the crystalline state and is luminescent in this phase; in solution, this compound exhibits dual band emission with a very large Stokes shift of 18 382 cm −1 attributed to an excited‐state intramolecular proton transfer (ESIPT) process. Time‐dependent density functional theory (TD‐DFT) and additional calculations are performed to evaluate the HOMO–LUMO distributions and theoretical absorption spectra, being in agreement with the experimental data. Additionally, the TD‐DFT calculations in solution (chloroform) show the ESIPT process and 8‐MR formation become thermodynamically favorable in 4b . This work represents the first synthesis of prompts feasibility ESIPT heterocyclic luminescent materials via an eight‐membered ring (8‐MR) with an N···HO connection.