Effects of End-Groups on Photophysical Properties of Poly(9,9-di‑n‑octylfluorene-2,7-vinylene)s Linked with Metalloporphyrins: Synthesis and Time-Resolved Fluorescence Spectroscopy

A series of poly­(9,9-di-n-octyl-fluorene-2,7-vinylene)­s (PFVs) containing metalloporphyrins at the chain ends with different conjugation lengths (ca. average 8 or 24 FV repeat units), PFV-[Por­(M)]2, have been prepared by olefin metathesis of the vinyl chain ends in PFVs (prepared by acyclic diene metathesis polymerization by ruthenium–carbene catalysts) using molybdenum–alkylidene catalyst (reagent) followed by Wittig-type cleavage with formyl porphyrin containing different metal ions [Zn­(II), Cu­(II), Ni­(II), and Pt­(II)]. Effects of the metalloporphyrins on photophysical properties of PFVs were studied by means of time-resolved fluorescence spectroscopy. The fluorescence spectral profile from PFV moiety in all the polymers with end-porphyrins was almost identical to that of the reference PFV. However, fluorescence quantum yields were remarkably lower, depending upon the central metal ion and the chain length. The observed reduction of the quantum yields is ascribed to intramolecular energy transfer to the end-groups as well as enhancement of intersystem crossing within the PFV unit. In the zinc derivative, PFV(High)-[Por­(Zn)]2, fluorescence from zinc porphyrin was also observed with a higher fluorescence quantum yield. It was found that radiative rate constant in zinc porphyrin moiety was enhanced about 3 times, suggesting specific interaction between the PFV and the porphyrin. On the other hand, time-resolved fluorescence signals of PFV moiety in all the PFV end-modified by metalloporphyrins decay with two or more components without any change of spectral profile. A model in which the excitation is localized in several pieces of FV units is proposed.