Color tunable, ratiometric pH sensor for high and low pH values base on 9-(cycloheptatrienylidene)fluorene derivatives

Novel absorption and fluorescence pH sensors based on 9-(cycloheptatrienylidene)fluorene (9-CHF) derivatives have been prepared by well-known Suzuki coupling reaction. 2,7-Bis(4-hydroxyphenyl)-9-CHF (4), 2-(4-hydroxyphenyl)-7-(naphthanlen-1-yl)-9-CHF (6) have the abilities to respond at both low (−1.0 → 2.0) and high (8.2 → 13.1) pH values and can be utilized in absorption, fluorescence, and wavelength ratiometric methods. They might be complements of the glass pH electrodes for pH measurement. More interestingly, 4 exhibts violet emission in low pH value range, blue emission in middle pH value range, and green emission in high pH value range, which presents a color tunable pH sensor.