Nortricarbocyanine dyes as suitable long wavelength pH indicators for chemical sensing

New norcyanine dyes were characterised for their use as long wavelength chromoionophores in optodes. Different membrane compositions were formulated for pH determination in water and their response in terms of sensitivity, linear range, response time and reversibility was examined with the aim to apply them in planar optochemical sensors. Their absorbance maxima are located in the NIR region (785–830 nm), which is very appropriate for applications using common low cost telecommunication components. The characterised optodes showed good analytical features. Hence, fully reversible, reproducible, fast, and sensitive bulk optodes were obtained. The photostability of dyes in the plasticised matrices and their tendency to leach from the membrane phase were also evaluated at different conditions.