20.500.12556/DiRROS-27351 Serendipitous discovery of nitrogen bridgehead fused pyridines photophysical properties and live-cell imaging potential A novel synthetic route to fluorescent nitrogen bridgehead fused pyridines (NBFPs) was discovered serendipitously during attempts to synthesize a thiazole derivative via a Hantzsch-type thiazole reaction from 2-cyanoethanethioamide and chloroacetone. A mechanism was proposed to rationalize the formation of NBFPs, which guided the subsequent expansion of the reaction scope and optimization of reaction conditions. The scope of the reaction was extended to include arylacetonitriles and esters of 2-(heteroaryl)acetic acids bearing an ortho-positioned pyridine-type nitrogen as a starting material. The structures of selected compounds were confirmed by single-crystal X-ray diffraction. All synthesized NBFPs exhibited pH-sensitive fluorescence and Stokes shifts exceeding 100 nm in several cases. Two compounds, methylthiazole derivative 1 and quinoline derivative 8, displayed pH-dependent emission suitable for lysosomal labelling. However, live-cell microscopy revealed limited colocalization with lysosomal probe Lysotracker Red, suggesting that these probes may localize to other acidic environments as well. Both compounds showed pronounced spectral responsiveness and fluorescence lifetime variations, indicating potential for use as environment-sensitive intracellular sensors. The methyl thiazole derivative 1 exhibited particularly favourable properties, including high photostability, low background fluorescence, minimal cytotoxicity and polarity sensitivity. These findings position NBFPs as a promising class of fluorophores for live-cell imaging and intracellular sensing applications, and warrant further investigation into their structure–function relationships and environmental responsiveness. nitrogen bridgehead fused pyridine Fluorescence pH sensitive probes live-cell imaging fluorescence lifetime imaging dušikov mostiček spojen s piridinom fluorescenca pH-občutljive sonde slikanje živih celic fluorescenčno slikanje v času trajanja true false true Elsevier Nizozemska Angleški jezik Slovenski jezik © 2026 The Author(s). Neznano 2026-02-03 10:07:11 2026-02-03 10:07:12 2026-02-04 04:07:10 0000-00-00 00:00:00 2026 0 0 Nasl. z nasl. zaslona; Opis vira z dne 2. 2. 2026; str. 1-9 [article no.] 117068 Vol. 476 Jul. 2026 0000-00-00 Zaloznikova Objavljeno NiDoloceno 2025-10-10 2026-01-25 2026-01-26 66.094.412 1873-2666 10.1016/j.jphotochem.2026.117068 266898691 https://www.sciencedirect.com/science/article/pii/S101060302600047X 1 cef4cac7-00df-11f1-93b0-001a4af901a5 https://dirros.openscience.si/Dokument.php?lang=slv&id=39967 RAZ_Kokot_Hana_2026.pdf RAZ_Kokot_Hana_2026.pdf 1 A8EB14E2303C5FD79FDA4C49E9788477 70df044ea77180020673317047d8e0d14ac3fd38c9d75a04e226c643efa94e3e 375f0400-00e0-11f1-93b0-001a4af901a5 https://dirros.openscience.si/Dokument.php?lang=slv&id=39968 Institut Jožef Stefan 0 0 0