Colorimetric fluorescence response to carbon dioxide using charge transfer dye and molecular rotor dye in smart solvent system

•A smart solvent system reacts to CO2 leading to changes in polarity and viscosity.•A charge transfer dye and a molecular rotor dye are used as probes in the solvent.•Combination of the two dyes displays a colorimetric fluorescence response to CO2.

Combination of a charge transfer dye and a molecular rotor dye in a smart solvent system resulted in a remarkable colorimetric fluorescence (FL) response to carbon dioxide (CO2). Nile Red and allyl-2-cyano-3-(1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinolin-9-yl)acrylate (ACHQA) were used as the charge transfer dye and molecular rotor dye, respectively, and an equivalent molar mixture of 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU) and 1-propanol was chosen as the smart solvent system. Nile Red and ACHQA in the DBU/1-propanol solvent mixture emitted red light mainly due to Nile Red, whereas the FL color gradually turned to green with the increasing amount of CO2 injected. The FL color reverted into the initial state by simultaneously bubbling N2 gas and heating at 50 °C.

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