(a) UV–vis and (b) photoluminescence (PL) spectra of Py-03, Py-MeO, Py-Me, and Py-Br in DCM; (c) PL spectra of the thin films of Py-03, Py-MeO, Py-Me, and Py-Br; and (d) PL spectra of Py-03, Py-MeO, Py-Me, and Py-Br measured at low temperatures
(77 K).