Reinvestigation of the synthesis of "covalent-assembly" type probes for fluoride ion detection. Identification of novel 7-(diethylamino)coumarins with aggregation-induced emission properties.

• Friedel-Crafts alkylation of 4-(diethylamino)salicylaldehyde was achieved. • Two novel 8-substituted 7-(diethylamino)coumarin dyes were synthesized. • These benzyl-substituted coumarin fluorophores exhibit remarkable AIE properties. An unprecedented C-3 functionalization of 4-(diethylamino)salicylaldehyde through a Friedel-Crafts type alkylation reaction has been discovered during the synthesis of "covalent-assembly"-based fluorescent probes for detection of fluoride ions. The resulting Friedel-Crafts adduct was successfully used for the preparation of two novel 8-substituted 7-(diethylamino)coumarin dyes. The photophysical study of these fluorophores has enabled us to highlight their remarkable aggregation-induced emission (AIE) properties characterized by a yellow-orange emission of aggregates in water. Therefore, 4-(tert -butyldimethylsilyloxy)benzyl substituent was identified as a novel AIE-active moiety which could be seen as a possible alternative to popular tetraphenylethylene (TPE). [ABSTRACT FROM AUTHOR]