Photophysical properties and singlet oxygen generation of meso-iodinated free-base corroles

In order to study the effect of meso-iodination of free-base corroles on their photophysical character, we designed and synthesized a series of free-base corrole derivatives F10-OH (iodine-free), F10-OH-I (mono-iodo) and F10-OH-2I (di-iodo), with different substitution patterns at the meso-position as candidates for photodynamic therapy (PDT). We employed several optical spectroscopic techniques, including time-resolved spectroscopy from a femtosecond to microsecond and singlet oxygen luminescence to study the properties of excited singlet and triplet states, as well as the singlet oxygen quantum yields. The sub-picosecond internal conversion, approximate to 1 ps intramolecular vibrational energy redistribution, tens of ps vibrational cooling, are similar across the three corroles. The addition of one (F10-OH-I) and two iodine (F10-OH-2I) atoms to the remote aryl ring of triarylcorroles induces a 4.6-fold and 6.2-fold decrease in fluorescence quantum yields phi(fl) and a 2.2-fold and 4.9-fold increase in the time constant of intersystem crossing k(ISC). In addition, a slight increase in intersystem crossing quantum yields phi(T) was also observed from F10-OH to F10-OH-2I. It means the intersystem crossing is improved by the iodination, from F10-OH to F10-OH-2I, because of the heavy atom effect. However, the sample F10-OH-I, instead of F10-OH-2I, shows the highest singlet oxygen quantum yield phi.