Novel pH-sensitive catechol dyes synthesised by a three component one-pot reaction

Area of Science:

• Organic Chemistry
• Materials Science

Background:

• Indolizine derivatives are known for their diverse applications.
• Catechol groups offer unique chemical properties for functionalization.

Purpose of the Study:

• To synthesize and characterize novel indolizine-based dyes containing catechol moieties.
• To evaluate the potential of these dyes as pH indicators.

Main Methods:

• A one-pot, three-component reaction involving pyridine-2-carbaldehyde, an aromatic alkyne, and a catechol-functionalized tetrahydroisoquinoline (THIQ).
• Copper nanoparticles on carbon (CuNPs/C) were used as a catalyst.
• UV-Vis and NMR spectroscopies were employed to study the pH-dependent behavior of the synthesized dyes.

Main Results:

• The synthesis yielded indolizine dyes with catechol groups in acceptable yields (30%-34%) without protecting the hydroxyl groups.
• Product 3aa displayed distinct color changes (light red to deep orange) across a pH range of 2-12.
• Spectroscopic analysis revealed two deprotonation events for product 3aa at pKa values of 4.4 and 9.5.

Conclusions:

• The synthesized indolizine dyes with catechol groups are effectively prepared via a straightforward synthetic route.
• Product 3aa demonstrates reversible pH-dependent color changes, indicating its suitability as a pH indicator.
• This new class of compounds holds potential for applications in chemical sensing and materials science.