Modular functionalization and hydrogel formation via red-shifted and self-reporting [2+2] cycloadditions.

We present a modularly applicable, red-shifted and self-reporting photodynamic covalent crosslinker, abbreviated qStyPy, that performs [2+2] cycloadditions upon irradiation with 470 nm in water. The rational design of qStyPy increases its hydrophilicity due to a permanent charge and features a broad emission in the far-red/near-infrared regime as a readout for the cycloadduct formation, rendering qStyPy suitable for biomedical applications.