Protonation, exciplex, and evidence of aggregate formation in meso-tetra(4-pyridyl) porphyrin triggered by excited-state absorption

Excited-state absorption (ESA) portraits a new pathway to controllably generate hexaprotonated (H8TPyP6+) porphyrins followed by the formation of a new species (possibly porphyrin aggregate) departing from pristine meso-(4-pyridyl) porphyrins (H2TPyP) dissolved in chloroform (CHCl3). Steady-state absorption and photoluminescence (PL) spectroscopies provide solid signatures for each step of the process. The photo-protonation mechanism involves CHCl3 decomposition driven by oxi-reduction reactions catalyzed by the H2TPyP itself. Time-resolved PL shows that the dispersion of chloride ions (Cl−) in the solution, which are remnant from the photo-triggered CHCl3 decomposition, leads to the quenching of both H2TPyP and H8TPyP6+ emission lifetimes. Stern-Volmer analysis suggests that the H8TPyP6+’s excited-state interactions with Cl− are non-emissive exciplex. Our findings open opportunities for the development of novel and controllable molecular processing strategies.