Design of large π-conjugated α-cyanostilbenes derivatives as colorimetric sensors for volatile acids and organic amines gases
Two large π-conjugated α-cyanostilbenes derivatives (M-PDC and P-PDC) were designed and synthesized through Knoevenagel condensation reaction between m-phenylenediacetonitrile, p-phenylenediacetonitrile and 4-(dimethylamino) cinnamaldehyde. Two α-cyanostilbenes derivatives were isomers, and their optical properties including absorption, emission, quantum yield and lifetime could be tuned by isomer effect. P-PDC exhibited an absorption band and emission peak all at larger wavelength than that of M-PDC under the same condition. Comparing with M-PDC, P-PDC had higher fluorescence quantum yield. Theoretical calculations demonstrated P-PDC possessed the lager π-conjugated system than that of M-PDC based on density functional theory (DFT) method. M-PDC and P-PDC with two dimethyl amine units as proton binding site showed the sensitively detection ability toward some volatile acids with certain acidity by naked eyes. For example, the limits of detection of solutions M-PDC and P-PDC in CH2Cl2 were 2.0 and 8.82 nM. Solutions M-PDC and P-PDC in CH2Cl2 with addition of TFA could detect some organic amines, and the limits of detection towards TEA were 1.76 and 3.47 nM. Solutions of M-PDC and P-PDC in CH2Cl2 were coated onto quartz plate and formed film with different morphologies, which emitted very weak light due to ACQ effect. But, fortunately, ACQ effect in films M-PDC and P-PDC could be overcome via introduction of CTAB, and exhibited great fluorescence enhancement by 225-fold and 105-fold, respectively. These results offered convenience for response volatile acids gases. The limit of detection of films M-PDC and P-PDC towards TFA was 17.4 and 2.37 ppm. Films M-PDC and P-PDC showed good reversibility through contacting volatile acids and organic amines gases in turn. This research will provide a new way for construction functional large π-conjugated system for detection gaseous acids and organic amines.