Diethyl 2-{4-diethylamino-2-[(dimethylcarbamothioyl)oxy]benzylidene}malonate

In the title compound, C21H30N2O5S, the plane of the dimethyl–thiocarbamic group makes a dihedral angle of 78.41 (7)° with the central benzene ring. One of the carbonyl groups in the α,β-unsaturated malonate side chain makes a dihedral angle of 8.73 (10)° with the central benzene ring, while the other carbonyl group makes a dihedral angle of 81.52 (8)°.

In the title compound, C 21 H 30 N 2 O 5 S, the plane of the dimethyl-thiocarbamic group makes a dihedral angle of 78.41 (7) with the central benzene ring. One of the carbonyl groups in the ,-unsaturated malonate side chain makes a dihedral angle of 8.73 (10) with the central benzene ring, while the other carbonyl group makes a dihedral angle of 81.52 (8) .

Comment
Reactive oxygen species (ROS) are known to be essential to several biological functions and hypochlorous acid (HOCl) is one of the biologically important ROS. Therefore, the determination of hypochlorous acid is very important for biological research, but it is still a challenge for the design and synthesis of highly specific and sensitive probes for hypochlorous acid (Sun et al., 2008). We have therefore synthesized the title compound, and investigated its fluorescent spectral response to hypochlorous acid, and further experiments show that the title compound can react with hypochlorous acid, which result in a remarkable fluorescence enhancement. Therefore, the title compound can serve as a sensitive fluorescent probe for the determination of hypochlorous acid. The chemical structures of related compounds (Jiang & Wang, 2009;Kim, & Swager 2003) have been reported, yet the crystal structures have not been reported. The title compound was obtained by two steps of chemical reactions. An X-ray crystal structure determination of the molecular structure of title compound was carried out to determine its conformation.
In the molecular structure of title compound (Fig.1), the plane of dimethyl-thiocarbamic group with the central benzene ring make a dihedral angle of 78.41 (7)° (Brandenburg, 2011). In addition, one carbonyl group in the a,b-unsaturated malonate side chain, make a dihedral angle of 8.73 (10)° with central benzene ring. The other carbonyl group, however, with the central benzene ring make a dihedral angle of 81.52 (8)°. The structure is therefore a conjugate electron system with "push-pull" substituent pairs, and shows strong intramolecular charge transfer (ICT) effects.

Experimental
The title compound was obtained from a two step synthesis. First, the reaction of 4-(diethylamino) salicylaldehyde and dimethyl thiocarbamoyl chloride under potassium carbonate in a DMF solution gave dimethyl-thiocarbamic acid O-(5-diethylamino-2-formyl-phenyl) ester. This product was refluxed for 3 h with diethyl malonate under the catalysis of piperidine in acetonitrile. After removal of the solvent, the residue was purified by flash chromatography with dichloromethane / petroleum ether as eluent to afford the title compound in 35% yield. The title compound exhibits an absorption maximum at 400 nm and in addition it also displays a minimal fluorescence emission at 509 nm with maximum excitation at 403 nm.
Single crystals were obtained by slow evaporation of a dichloromethane / petroleum ether (5/1, v/v).

Refinement
The aromatic H atoms were generated geometrically (C-H 0.93, N-H 0.86 Å) and were allowed to ride on their parent atoms in the riding model approximations, with their displacement factors set to 1.2 times those of the parent atoms. as those based on F, and R-factors based on ALL data will be even larger.