Synthesis of a Highly Fluorescent Quinoxalino[2,3-b]quinoxaline Polycyclic Derivative via Intramolecular Michael Addition to a Squaramide Ring

Picci G.

First

;Milia J.;Lippolis V.;Ricci P. C.;Frontera A.;Gomila R. M.;Ojah E. O.;De Silva Weerakonda Arachchige R. D.;Orton J. B.;Coles S. J.;Busschaert N.

;Caltagirone C.

2026-01-01

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Abstract

In the presence of TBAOH, bis-indolylsquaramide (1) converts into the highly emissive, novel bis(3H-pyrrolo[1,2,3-de]quinoxaline) exa-cyclic derivative 2. This compound was fully characterized in solution and the solid state, with emission properties supported by DFT calculations. Derivative 2 exhibits high quantum yield in solution with aggregation-induced quenching, and a large spectral shift between solid state and solution. Reaction conditions were optimized, and a mechanism involving a double intramolecular Michael addition triggered by deprotonation, oxidation and photodecarbonylation was proposed on the basis of DFT calculations and LC-MS measurements. In addition to reporting a novel, highly pi-conjugated emissive compound, this manuscript highlights an unprecedented squaramide reactivity under basic conditions, resulting in the first example of intramolecular quinoxaline moiety formation from a squaramide derivative.