NIR-emitting aza-BODIPY dyes – new building blocks for broad-range optical pH sensors†
New aza-BODIPY indicators which cover the pH scale from 1.5 to 13 are presented. The new indicators feature absorption/emission bands in the red/near-infrared (NIR) spectral region, exhibit high molar absorption coefficients (∼ 80 000 M−1 cm−1) and show good quantum yields (∼20%). All dyes represent promising building blocks for the development of a broad-range sensor for various pH ranges. Combination of four of these pH indicators yields a pH sensor with an extended dynamic range from pH 2 to 9.