A unique combination of two independent mechanisms of fluorescence quenching, namely intramolecular charge transfer (ICT) from a peripheral donor and protonation of azomethine nitrogen atoms in zinc tetrapyrazinoporphyrazines (TPyzPz), provides a new possibility for sensing pH in a specific range. The pH selectivity was controlled by the different basicities of the donor for ICT (dimethylaminoaryl), which was connected to the macrocycle by π-extended linkers of different lengths. ICT and protonation have been studied in detail by photophysical, spectral (UV/Vis and MCD spectra), and electrochemical measurements, and further supported by theoretical calculations (DFT, TDDFT). The pH-sensing properties of the TPyzPzs have been investigated in THF and in water after anchoring the TPyzPzs to liposomes. The salient pKa values were around 1.3 (azomethine nitrogen) and 2.29-4.76 (donor for ICT). The lead indicators (sensing over a pH range of 1.0-2.5) with fairly steep sensing profiles exhibited increases in fluorescence between the OFF/ON states of more than 20-fold and strong absorption in the red region (Q-band maximum >650 nm, ϵ≈2×106 m-1 cm-1 ).

Department of Biophysics and Physical Chemistry Faculty of Pharmacy in Hradec Kralove Charles University Prague Heyrovskeho 1203 Hradec Kralove 500 05 Czech Republic

Department of Chemistry and Biochemistry University of Minnesota Duluth 1039 University Drive Duluth MN 55812 USA

Department of Chemistry University of Manitoba Winnipeg MB R3T 2N2 Canada

Department of Pharmaceutical Chemistry and Pharmaceutical Analysis Faculty of Pharmacy in Hradec Kralove Charles University Prague Heyrovskeho 1203 Hradec Kralove 500 05 Czech Republic

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