New hexamethine-hemicyanine dyes for the development of integrated optochemical sensors

New far-visible absorbing anilino-cyanine dyes have been synthesised for future application as chromoionophores in integrated waveguide absorbance optodes based on bulk optodes. The effect of the heterocycle, of the substitution of the heterocyclic nitrogen and of the type of heptamethine central ring on the pKa values (4.3-8.2 in ethanol-water solutions and 9.5-11.0 in plasticised PVC membranes), on the spectroscopic characteristics of the dye and on photostability is discussed. pH-selective bulk optodes have been formulated as a first approach to develop ion-selective optodes, and sensitivity, repeatability, lifetime and response time have been determined. The dyes show good analytical behaviour for use as chromoionophores for the development of ion-selective optodes. Reversible (80-87%), fast (tr90%=0.94-2.28 min) and pH-sensitive membranes (slopes of 0.09-0.23 DeltaAbs.pHdec-1, absorbance range 0.19-0.53) have been obtained. Moreover, they exhibit good spectroscopic features for employment with integrated optochemical sensors: absorption maxima of the acidic species in plasticised PVC membranes matched those of 650-670-nm LEDs, high molar absorption coefficients (epsilonacidic=3.5x10(4)-9.3x10(4) L mol-1 cm-1 and epsilonbasic=1.9x10(4)-6.7x10(4) L mol-1 cm-1) and fluorescence.