Having a mirror-image profile to that of the lowest energy absorption band, the PL spectra have a lower intensity, lower energy shoulder, which is typical for vibrational sub-states. Despite the broadening induced by the shoulder, the full width at half-maximum (FWHM) of each emission band is extremely narrow, ranging from 27 nm in 4NICz, to just 22 nm in 5NICz. In air, the photoluminescence quantum yield, ΦPL, of the emitters ranges from 50% for 6NICz, to 15% (7NICz) 12% (5NICz), 12% (6,10NICz), and 6% (4NICz). Under deaerated conditions, the FPL of 4NICz, 5NICz and 7NICz increase by a factor of 1.8, 2.0, and 1.6 respectively, while the FPL of 6NICz and 6,10NICz remained relatively constant, changing by only a factor of 1.1 and 1.3, respectively (Table ).