Ratiometric fluorescent/colorimetric cyanide-selective sensor based on excited-state intramolecular charge transfer-excited-state intramolecular proton transfer switching.

A novel salicylideneaniline-based fluorescent sensor, SB1, with a unique excited-state intramolecular charge transfer-excited-state intramolecular proton transfer (ESICT-ESIPT) coupled system was synthesized and demonstrated to fluorescently sense CN(-) with specific selectivity and high sensitivity in aqueous media based on ESICT-ESIPT switching. A large blue shift (96 nm) was also observed in the absorption spectra in response to CN(-). The bleaching of the color could be clearly observed by the naked eye. Moreover, SB1-based test strips were easily fabricated and low-cost, and could be used in practical and efficient CN(-) test kits. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations further support the cyanide-induced ESICT-ESIPT switching mechanism. The results provide the proof of concept that the colorimetric and ratiometric fluorescent cyanide-selective chemodosimeter can be created based on an ESICT-ESIPT coupled system.

1-Meth-oxy-11H-benzo[b]fluoren-11-one.

In the title compound, C18H12O2, the non-H atoms are nearly coplanar, the maximum atomic deviation being 0.113 (2) Å. π-π stacking is observed in the crystal structure, the shortest centroid-centroid distance being 3.5983 (19) Å. The mol-ecular packing is further stabilized by weak C-H⋯O hydrogen bonds, forming an infinite chain along [100] and generating a C(6) motif.

2-(Dibromo-meth-yl)benzoic acid.

In the crystal structure of the title compound, C(8)H(6)Br(2)O(2), the carboxyl groups are involved in pairs of O-H⋯O hydrogen bonds, which link the mol-ecules into inversion dimers.

1,2-Bis(dibromo-meth-yl)benzene.

In the title compound, C(8)H(6)Br(4), intra-molecular C-H⋯Br hydrogen bonds generate two S(6) rings. The two geminal bromine-atom substituents point to opposite sides of the aromatic ring system. In the crystal, mol-ecules are linked by inter-molecular π-π inter-actions with centroid-centroid distances of 3.727 (9) and 3.858 (9) Å.

4-Hy-droxy-indan-1-one.

The mol-ecule of the title compound, C(9)H(8)O(2), is essentially planar except for the methyl-ene H atoms [maximum deviation = 0.028 (1) Å]. In the crystal, the mol-ecules are linked by classical O-H⋯O hydrogen bonds and weak C-H⋯O inter-actions into chains along [110] and [1-10].