Electronic Energy Transfer in a Multiporphyrin-based Molecular Box

The molecular box 1 comprises of two zinc-porphyrin metallacycles connected bytwo free-base 4'-trans-dipyridylporphyrins, axiallycoordinated to the zinc centers. The photophysics of 1 were studied in chloroform byemission and ultrafast absorption spectroscopy. In the molecular box, fast singlet energy transfer (main component, t=32 ps) is observed to occur from the zinc-porphyrin metallacycles to the free-base chromophores. From wavelength- dependent spectrofluorimetric data, the efficiencyof the energy-transfer (ET) process is estimated as 0.5. The lower-thanunityvalue is tentativelyattributed to the possibilityof a competing electron-transfer quenching pathway. Molecular box 1 can be considered to be a simple, self-assembling, six-chromophore antenna system. It has an inner cavity, 11.4 < wide, that could be used, in principle, to host a varietyof guest molecules and obtain higher-order assemblies.