Exploring the reactivity of formylporphyrins with 3-(diethylamino)phenol: synthesis, spectroscopic properties and singlet oxygen generation of a new porphyrin–rosamine conjugate

The design of novel molecular structures with tunable photophysical properties is an important research field for many applications including optoelectronics, sensing and bioimaging. Porphyrin and rhodamine/rosamine derivatives are among the most studied and relevant chemosensors and imaging probes due to their attractive photophysical properties, such as high absorption coefficients and long emission wavelengths. In this work, we present the synthesis and the structural characterization of a new porphyrin–rosamine conjugate H2P3 and its related triarylmethane precursors H2P1 and H2P2. The photophysical properties of H2P1, H2P2 and H2P3, and their ability to chelate iron(III) and copper(II) ions, were evaluated by absorption and emission spectroscopy. The formation of copper(II) complexes was confirmed by electron paramagnetic resonance (EPR), which also allowed the detection of an intense and stable radical signal for the free-base H2P3. Further studies involving the addition of the 2,2,6,6-tetramethylpiperidine spin trap to derivatives H2P1, H2P2 and H2P3, showed that only H2P3 gives rise to an EPR detectable signal due to a strong generation of singlet oxygen.