Rofecoxib derivatives as NIR fluorescent probes for mitochondrial viscosity and in vivo imaging of Aβ plaques

•Two fluorescent probes, RC-1 and RA-2 are rationally designed and synthesized based on the Rofecoxib scaffold.•RC-1 and RA-2 exhibit turn-on NIR fluorescent emission toward Aβ aggregates.•RC-1 and RA-2 have been successfully used to monitor mitochondrial viscosity variations under abnormal conditions.•RC-1 achieves in vivo imaging of Aβ plaques in the brain of AD mice.