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

## TL;DR

This paper describes the creation of a new fluorescent compound through a unique chemical reaction involving squaramide.

## Contribution

The study introduces a novel emissive compound and a new reactivity pathway for squaramides under basic conditions.

## Key findings

- Derivative 2 shows high quantum yield in solution and aggregation-induced quenching.
- A mechanism involving double intramolecular Michael addition was proposed.
- The compound exhibits a large spectral shift between solid state and solution.

## 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 π-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.