A series of novel monodisperse, well-defined, star-shaped molecules T(OCA
n)Ps (
n = 2-6) with a centralporphyrin core and four oligocarbazole arms are synthesized from the corresponding formyl-substitutedoligocarbazoles via Adler reaction. The obtained star-shaped porphyrins are intrinsically two-dimensionalnanosized molecules, and the diameter of compound T(OCA6)P is 7.4 nm, representing one of the largestknown star-shaped conjugated systems. Their photophysical properties have been investigated by absorptionand steady-state fluorescence spectroscopy, together with the corresponding monodisperse oligocarbazolealdehyde precursors. It is found that the light-harvesting capability of T(OCA
n)Ps increases with theincreasing length of the arms and reaches the maximum when
n = 6. A selective excitation of theoligocarbazole arms leads to the typical emission from the porphyrin cores, indicating occurrence ofphotoinduced intramolecular energy transfer, and the energy transfer efficiency decreases from T(OCA2)Pto T(OCA6)P owing to the Förster energy-transfer process. Accordingly, the longest effective distancefor Förster energy transfer is estimated to be ca. 3 nm in our system. Such star-shaped porphyrins mayfind applications in photonic devices, with respect to their intense emission of red light. Notably, themonodisperse oligocarbazole aldehyde precursors give twisted intramolecular charge-transfer (TICT)excited states and luminescence in polar solvents with large Stokes shifts.
