New fluorescent perylene bisimide indicators--a platform for broadband pH optodes

Asymmetric perylene bisimide (PBI) dyes are prepared and are shown to be suitable for the preparation of fluorescence chemosensors for pH. They carry one amino-functional substituent which introduces pH sensitivity via photoinduced electron transfer (PET) while the other one increases solubility. The luminescence quantum yields for the new indicators exceed 75% in the protonated form. The new indicators are non-covalently entrapped in polyurethane hydrogel D4 and poly(hydroxyalkylmethacrylates). Several PET functions including aliphatic and aromatic amino groups were successfully used to tune the dynamic range of the sensor. Because of their virtually identical spectral properties, various PBIs with selected PET functions can easily be integrated into a single sensor with enlarged dynamic range (over 4 pH units). PBIs with two different substitution patterns in the bay position are investigated and possess variable spectral properties. Compared with their tetrachloro analogues, tetra-tert-butyl-substituted PBIs yield more long-wave excitable sensors which feature excellent photostability. Cross-sensitivity to ionic strength was found to be negligible. The practical applicability of the sensors may be compromised by the long response times (especially in case of tetra-tert-butyl-substituted PBIs).