Fig. 2: Absorption spectra and emission spectra of compounds 1–6.

Absorption spectra of (a) compound 1 and 4, (c) 2 and 5, (e) 3 and 6. Emission spectra of (b) 1 and 4 (λ_ex = 640 nm), (d) 2 and 5 (λ_ex = 469 nm), (f) 3 and 6 (λ_ex = 403 nm) in ethanol. Fl fluorescence.