Novel lysosome-targeted fluorescent molecular rotors based on a cyanine-like modular system and their application in living cells

Insights into extended coupled polymethines through the investigation of dual UV-to-NIR acidochromic switches based on heptamethine–oxonol dyes

“…As already mentioned, the original work describing the preparation of dsp-1 did not indicate the opening of the compound under acidic conditions, 41 and the more recent report of a closely related analogue of 1·H + did not identify either the dicationic or spirocyclic forms of the dye at low and high pH conditions, respectively. 40 In our case, the cationic or dispiropyran forms of compounds 1 and 2 were successfully isolated using either acidic or basic treatment of the reaction and both forms could be easily differentiated. Firstly, the appearance of compounds 1 and 2 in solution markedly varies from green for the cationic species to colourless for the less conjugated dispiropyrans.…”

“…The condensations of 6 with 2 equivalents of indoleniums 7 or 8 were first carried out in ethanol using piperidine as base, following a recently published protocol reporting the isolation of cationic 1·H + after acid hydrolysis and recrystallization. 40 Surprisingly, in our case the recrystallisation step was unsuccessful and we had to resort to column chromatography on silica gel to isolate the desired compounds 1·H + and 2·H + with low yields ( ca . 10%).…”

“…2C) were recently synthesized by He, Zeng, and co-workers for selective mitochondria or lysosome staining. 39,40 However these two reports did not identify either the zwitterionic species ( z-3 ) or any spirocyclic isomer ( e.g. dsp-1 ) forming at high pH values ( vide infra ).…”