Neutral and ionic N -methyl phenylazo-3,5-(di-2-pyridyl)pyrazole photoswitches: probes for reversible pH modulation by light.

We report the design, synthesis, photoswitching and computational studies of N -methyl arylazo-3,5-(di-2-pyridyl)pyrazole and its N -alkyl pyridinium derivatives with an ionic center proximally located to the azo group. Besides achieving excellent photoswitching characteristics, particularly at longer wavelengths, and tuning Z isomer stability due to the effects of counter ions and pH, the utility of neutral and ionic photoswitches for pH modulation by light was achieved.