A new far-red naphthorhodamine dye: Synthesis, fluorescent probe and bioimaging applications

A new extended-pi-conjugated naphthorhodamine dye, 9'-diethylamino-2'-hydroxyl-benzo[a]fluoran (1) with a carboxylic acid-functional group was designed and synthesized. Compared to Rhodamine B, the emission wavelength of 1 was extended to ca. 600 nm, and its fluorescence properties could be controlled by the key carboxylic acid-functional group. By taking advantage of 1, we synthesized a new far-red bioimaging dye 2-ethyl-9'-diethylimino-2'-hydroxyl- benzo[a]fluoran (2) by esterification of 1, which could selectively stain mitochondria. Moreover, encouraged by the spirocyclization switching mechanism platform, we successfully constructed a new fluorescent probe 9'-diethylamino-2'-hydroxyl-benzo[a]fluoran hydrazine (3), the hydrazide derivative of 1, for Hg2+ with good selectivity. These results suggest that the new naphthorhodamine dye could be used as a platform to construct fluorescent probes and bioimaging reagents. (C) 2016 Elsevier Ltd. All rights reserved.