| Abstract
| - The Pd-mediated Glaser coupling of a zinc monoethynyl porphyrin and a magnesium monoethynylporphyrin affords a mixture of three 4,4‘-diphenylbutadiyne-linked dyads comprised of two zincporphyrins (Zn-pbp-Zn), two magnesium porphyrins (Mg-pbp-Mg), and one metalloporphyrin ofeach type (Zn-pbp-Mg). The latter is easily isolated due to the greater polarity of the magnesiumversus the zinc chelate. Exposure of Zn-pbp-Mg to silica gel results in selective demetalation,affording Zn-pbp-Fb where Fb = free base porphyrin. This synthesis route employs the magnesiumporphyrin as a latent form of the Fb porphyrin, thereby avoiding copper insertion during the Glaserreaction, and as a polar entity facilitating separation. The absorption spectrum of Zn-pbp-Mg orZn-pbp-Fb is the sum of the spectra of the component parts, while in each case the fluorescencespectrum upon illumination of the Zn porphyrin is dominated by emission from the Mg or Fbporphyrin. Time-resolved absorption spectroscopy shows that the energy-transfer rate constantsare (11 ps)-1 and (37 ps)-1 for Zn-pbp-Mg and Zn-pbp-Fb, respectively, corresponding to energy-transfer quantum yields of 0.995 and 0.983, respectively. The calculated Förster through-spacerates are (1900 ps)-1 and (1100 ps)-1 for Zn-pbp-Mg and Zn-pbp-Fb, respectively. Accordingly,the through-bond process dominates for both dyads with a through-bond:through-space energy-transfer ratio of ≥97:1. Collectively, the studies show that the 4,4‘-diphenylbutadiynyl linkersupports fast and efficient energy transfer between Zn and Mg or Fb porphyrins.
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