A novel dye chemosensor based on indole as a donor unit and quinaldium as an acceptor unit have caused promising optical changes when used as a reversible, pH-induced, molecular switching in the presence of alkali/acid stimulus. The dye chemosensor also exhibited marked fluorescence quenching in the presence of alkali addition, which are based on intramolecular charge transfer (ICT) system. The level of energy potential and the electron flowing of this dye chemosensor such as HOMO and LUMO values were calculated by computational calculation approaches.