The emission color purity is also outstanding. Distinct from other organic phosphors, the FWHM of the RTP was 29 nm for 1a, and the intensity of the second vibrational band at 615 nm was only 25% of that at 560 nm (Figures and and Table ). As a result of the narrowband RTP and the fluorescence-free nature, the high color purity was achieved as represented by its coordinates (0.45, 0.54) located almost at the edge of the chromaticity diagram of Commission internationale de l'éclairage (CIE) 1931 (Figure ). Furthermore, introducing trialkylsilyl substituents (triisopropylsilyl for 1b and tributylsilyl for 1c) produced a slight red shift from 560 nm to 568 nm in the emission maxima, while maintaining a small FWHM (32 nm). This pure yellow narrowband emission had a CIE coordinate of (0.49, 051) (Figure ). 2c p and kp values for 1b and 1c were less, but still 24.6% (5000 s -1 ) and 17% (4500 s -1 ), respectively. The decrease in p could be attributed to the doubled knr values, from 8500 s -1 for 1a to 15000 s -1 and 22000 s -1 for 1b and 1c, respectively. This was most likely because of the molecular motion by the silyl groups.