TY - JOUR A1 - Rurack, Knut A1 - Maus, M. T1 - Monitoring pH and solvent proticity with donor-acceptor-substituted biphenyls: a new approach towards highly sensitive and powerful fluorescent probes by tuning the molecular structure N2 - The ability and structural requirements of 4-dimethylamino-4-cyano-substituted biphenyls showing photoinduced intramolecular charge transfer (CT) to serve as hydrogen bond- or pH-sensitive fluorescent probes is investigated. The donor–acceptor (D–A) biphenyls I and II being planar in the CT excited state are most suitable as pH-sensitive fluorescent probes. The two compounds show analytically valuable features such as well-separated absorption and emission bands and signal changes spanning four orders of magnitude and can be employed in ratiometric, self-calibrating, and highly sensitive pH fluorosensing in the range 0