High performance optical trace oxygen sensors based on NIR-emitting benzoporphyrins covalently coupled to silicone matrixes

• New Pt(II)- and Pd(II)-benzoporphyrin indicator were prepared via 3 simple reaction steps.
• Modification of these dyes via Suzuki-coupling to introduce styrene groups for covalent coupling to the sensor matrix is performed.
• Highly robust silicone rubber sensor materials were prepared using catalytic hydrosilylation reaction.
• Linear calibration plots simplify calibration and recalibration of the sensor.
• Oxygen sensitivity is fine-tuned by using differently substituted silicone pre-polymers.

New robust optical sensors for measurement of low oxygen concentrations are presented. The simple synthesis of a new Pt(II) and Pd(II)-benzoporphyrin indicator and the subsequent modification via Suzuki-coupling to introduce reactive styrene groups are shown. These indicators have excellent photophysical properties like high brightness, good photostability and NIR emission. A highly mechanically and chemically stable oxygen-permeable silicon rubber matrix was prepared by curing polysiloxane pre-polymers using the catalytic hydrosilylation reaction. The new indicator dyes act as crosslinkers in this reaction and are covalently immobilised into the matrix which prevents aggregation and leaching of the dye. Differently substituted polysiloxane pre-polymers were used in order to fine-tune the sensitivity of the sensor. In contrast to most state-of-the-art oxygen sensors the Stern–Volmer plots are ideally linear in the relevant measurement range which ensures simple (re)calibration. The sensors show very fast response <1 and KSV values between 0.082 and 0.141 hPa−1 when using Pt(II)-benzoporphyrin and 0.921 hPa−1 when using Pd(II)-benzoporphyrin. To illustrate potential applications of these oxygen sensors, the measurement of oxygen diffusion through cork-sealed colored glass bottles is demonstrated.

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