Dependent excited state absorption and dynamic of b-BF2 substituted metalloporphyrins: The metal ion effect

Absorption and relaxation dynamics of electronic states of free-base, Co(II), Cu(II) and Zn(II) porphyrins bearing a b-(2,2-difluoro-1,3,2-dioxaborinin-5-yl) group were investigated in dimethyl sulfoxide by using distinct time-resolved spectroscopic techniques. Furthermore, excited state absorption cross-section spectra were determined by combining white light continuum Z-Scan and transient absorption techniques. In the case of the free-base (2H) and Zn(II) porphyrins, we were able to quantify singlet-triplet conversion by analyzing the evolution of time-resolved fluorescence. Relaxation lifetimes from the excited to the ground state were observed in both porphyrins at nanosecond time scale. However, for Co(II) and Cu(II) metalloporphyrins it was observed in the picosecond time scale through femtosecond transient absorption, indicating that both compounds relax back to the ground state only by internal conversion processes. Co(II) and Cu(II) heavy atoms seem to prohibit the radiative and intersystem crossing processes. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

The absorption and relaxation dynamics of electronic states of porphyrins with b-(2,2-difluoro-1,3,2-dioxaborinin-5-yl) group were investigated in this study. The singlet-triplet conversion was quantified in free-base and Zn(II) porphyrins, while Co(II) and Cu(II) porphyrins showed relaxation back to the ground state only by internal conversion processes. Heavy atoms in Co(II) and Cu(II) seemed to prohibit radiative and intersystem crossing processes.