New 1,2-Dihydropyridine-Based Fluorophores and Their Applications as Fluorescent Probes

New 1,2-dihydropyridine (1,2-DHP)-based fluorophores 1a–1h were designed and synthesized by a one-pot four-component condensation reaction using dienaminodioate, aldehydes, and an in situ-generated hydrazone mediated by trifluoroacetic acid. The photophysical properties of 1,2-DHPs were studied in detail, and a few of them exhibited selective mitochondrial staining ability in HeLa cell lines (cervical cancer cells). A detailed photophysical investigation led to the design of 1,2-DHP 1h as an optimal fluorophore suitable for its potential application as a small molecule probe in the aqueous medium. Also, 1,2-DHP 1h exhibited sixfold enhanced emission intensity than its phosphorylated analogue 1h′ in the long wavelength region (λ_em ≈ 600 nm), which makes 1,2-DHP 1h′ meet the requirement as a bioprobe for protein tyrosine phosphatases, shown in L6 muscle cell lysate.