Truxene-cored pi-expanded triarylborane dyes as single- and two-photon fluorescent probes for fluoride

Fluoride anion (F-) significantly affects chemical, biological, and environmental processes. Fluoride recognition and detection have received increasing attention. Convenient, effective, and sensitive fluorescent probes for F- should urgently be designed and synthesized. In this study, we describe a strategy for constructing two triarylborane-based fluoride fluorescent probes: 2,7,12-tri(2-(5( dimesitylboryl) thiophen-2-yl) ethynyl)-5,5',10,10',15,15'-hexaethyltruxene (C3B3) with pi-3A (acceptor) configuration and 2,7-di(N, N-diphenylamino)-12-(5-(dimesitylboryl) thiophen-2-yl)-5,5',10,10',15,15'-hexaethyltruxene (N2SB) with 2D (donor)-pi-A configuration. The loss of color of the tetrahydrofuran solution of these probes from greenish yellow suggests that they can conveniently monitor F- at a low concentration (10 mu M) free of apparatus. The different structural features of these probes varied their fluorescent responses to F-. The single-photon fluorescence intensity of C3B3 declined to 90% upon the addition of 4.5 equivalents of F- to its tetrahydrofuran solution. However, the single-photon fluorescence intensity of N2SB was enhanced six-fold upon addition of 2.5 equivalents of the F-. Under the experimental conditions, the detection limits of the two probes for F- can reach 12-13 mu M (C3B3) and 3-5 mu M (N2SB). The ability of the two probes in detecting F- in their toluene solutions in the twophoton mode was also investigated. The sensitive two-photon fluorescence responses of both probes make them excellent two-photon fluorescence probes.