title: OFF-ON-OFF Red-Emitting Fluorescent Indicators for a Narrow pH Window.
abstract: 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 pKavalues 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≈2×106m-1cm-1).
authors.affiliation: Department of Pharmaceutical Chemistry and Pharmaceutical Analysis, Faculty of Pharmacy in Hradec Kralove, Charles University in Prague, Heyrovskeho 1203, Hradec Kralove, 500 05, Czech Republic.
authors.forename: Antonin
authors.initials: A
authors.lastname: Cidlina
authors.affiliation: Department of Pharmaceutical Chemistry and Pharmaceutical Analysis, Faculty of Pharmacy in Hradec Kralove, Charles University in Prague, Heyrovskeho 1203, Hradec Kralove, 500 05, Czech Republic.
authors.forename: Miroslav
authors.initials: M
authors.lastname: Miletin
authors.affiliation: Department of Chemistry and Biochemistry, University of Minnesota, Duluth, 1039 University Drive, Duluth, MN, 55812, USA.
authors.forename: Mahtab
authors.initials: M
authors.lastname: Fathi-Rasekh
authors.affiliation: 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.
authors.forename: Victor N
authors.identifier: http://orcid.org/0000-0003-4345-0848
authors.initials: VN
authors.lastname: Nemykin
authors.affiliation: Department of Pharmaceutical Chemistry and Pharmaceutical Analysis, Faculty of Pharmacy in Hradec Kralove, Charles University in Prague, Heyrovskeho 1203, Hradec Kralove, 500 05, Czech Republic.
authors.forename: Petr
authors.identifier: http://orcid.org/0000-0002-3533-3601
authors.initials: P
authors.lastname: Zimcik
authors.affiliation: Department of Biophysics and Physical Chemistry, Faculty of Pharmacy in Hradec Kralove, Charles University in Prague, Heyrovskeho 1203, Hradec Kralove, 500 05, Czech Republic.
authors.forename: Veronika
authors.identifier: http://orcid.org/0000-0002-2183-1220
authors.initials: V
authors.lastname: Novakova
keywords: azomethine nitrogen; fluorescence; intramolecular charge transfer; phthalocyanines; sensors