Thiazole-linked π-conjugated frameworks synthesized via sequential Pd-catalyzed arylation: synthetic strategy and structure-property correlations.

Authors

Pranali Prabhakar Thakur, Mahendra Patil

Published in

Organic & biomolecular chemistry. Aug 03, 2026. Epub Aug 03, 2026.

Abstract

A versatile palladium-catalyzed sequential arylation strategy has been developed for the efficient synthesis of structurally diverse 2,5-diarylated thiazoles (4a-4s). This modular approach enabled the synthesis of three distinct substitution motifs, donor-A-donor (D-A-D, Series I), acceptor-π-donor (A-π-D, Series II), and donor-π-acceptor (D-π-A, Series III), with thiazole serving as the electronically active bridge. Regioselective C5 and C2 arylation, achieved under tailored conditions, offered broad functional-group tolerance, accommodating both electron-rich donors and electron-deficient acceptors. The method delivered the targeted scaffolds in moderate to excellent yields (40-70%), underscoring both its synthetic efficiency and broad applicability. Comprehensive photophysical studies established clear structure-property relationships. D-A-D systems showed localized π-π* absorption with moderate emission, whereas A-π-D systems displayed pronounced intramolecular charge transfer (ICT), with several derivatives, most notably 4j (TPA donor), achieving near-unity fluorescence quantum yields (Φ_F = 89%). Importantly, the D-π-A framework also exhibited strong ICT, evidenced by substantial Stokes shifts (up to 7660 cm^-1), extensive solvatochromic responses, and red-shifted, tunable emission extending into the green-yellow region (420-550 nm). The Lippert-Mataga and Bilot-Kawski analyses confirmed pronounced excited-state dipole reorganization in representative compounds such as 4b, 4j, 4m, and 4q, thereby identifying them as sensitive, polarity-responsive fluorophores. Conversely, anthracene-substituted thiazoles, despite their intense absorption, showed low quantum yields. Overall, this work demonstrates the strategic utility of Pd-catalyzed sequential arylation in accessing a versatile library of thiazole fluorophores. By integrating synthesis, photophysical and solvatochromic studies, and DFT analysis, we validate thiazole as a versatile π-bridge scaffold with significant potential for OLEDs, laser dyes, and fluorescence sensing platforms.

PMID:
42544485
Bibliographic data and abstract were imported from PubMed on 03 Aug 2026.

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