When the solvent was switched to EtOH, we observed bright fluorescence and no scatter peak (Table ). Dioctadecylsilyl dye 15 was poorly soluble and its fluorescence properties were not further characterized. Potentially, however, such long-chain aliphatic groups could be used to recruit Si-dyes to membranes. Si-substitution effects extend generally to different Si-rhodamine scaffolds. We next evaluated the effect of modified silyl groups in a broader range of Si-rhodamine dyes with different amine donors (Schemes 1, 2). The previously reported dimethylsilyl dyes SiR680 (18) and SiR700 (22) incorporate rigid tetrahydroquinolines and indolines respectively, which red-shifts their fluorescence properties compared to 4. Notably, we found that the red-shifting effects of Simodification are additive within these scaffolds. Divinylsilyl (19) and diphenylsilyl (20) SiR680 dyes are 9-18 nm further red-shifted from SiR680 (18) (Table ). Similarly, the divinylsilyl (23) and diphenylsilyl (24) indoline SiR700 dyes are red-shifted by 12-22 nm, and 23 is brighter than the dimethylsilyl dye SiR700 (22). Among these dyes, 19 is a particular standout, as it is redshifted and 60% brighter than 18 (Table ).