“…The lower wavelength at 242 nm was ascribed to the π-π* transition which is theoretically predicted at 247 nm [63][64][65][66] while the strong absorption peak at 332 nm (calculated at 349 nm) was assigned to the n-π* absorption bands of the 2,6diaminopyridinium [53]. Infact, the direct and indirect optical band gap energy of the title compound can be calculated by simply plotting (αhν) 2 versus (hν) and (αhν) 1/2 versus (hν), according to the Tauc relation [67]:…”