Bis-ratiometric absorbance detection of Al(III) in the rhodamine B-functionalized bis-polydiacetylene film

A rhodamine B-functionalized bis-polydiacetylene (RB/bis-PDA) film sensor was prepared. Rhodamine B derivatives as the ion-recognition elements were embedded in the bis-polydiacetylene matrix through the hydrolysis/condensation process of organic silicon. The as-prepared blue-phase RB/bis-PDA film could transfer to yellow phase at high temperatures. Upon dipping the blue and yellow RB/bis-PDA films into various metal ion solutions, respectively, only Al³⁺ could induce remarkable changes in absorption and color signals. The UV–Vis absorption spectrum of the Al³⁺-containing film showed two separate absorption peaks at 556 nm and at another wavelength (617 or 470 nm), corresponding to ring opening of the spirolactam structure in rhodamine moiety and PDA (blue- or yellow-phase PDA), respectively. Utilizing the different intensity ratios of the two absorption signals (A₅₅₆/A₆₁₇ or A₅₅₆/A₄₇₀), the RB/bis-PDA system could be used as a bis-ratiometric absorbance sensor for Al³⁺. The reusable and free-standing films have great potential in environmental and biological sensing fields as they are more convenient to achieve real-time sensing than the conventional probes dissolved in aqueous or organic solvents.