Energy‐ and Charge‐Transfer Processes in a Perylene–BODIPY–Pyridine Tripartite Array

Abstract

AbstractA novel boron dipyrromethene (BODIPY) dye has been synthesized in which the F atoms, usually bound to the boron center, have been replaced with 1‐ethynylperylene units and a 4‐pyridine residue is attached at the meso‐position. The perylene units function as photon collectors over the wavelength range from 350 to 480 nm. Despite an unfavorable spectral overlap integral, rapid energy transfer takes place from the singlet‐excited state of the perylene unit to the adjacent BODIPY residue, which is itself strongly fluorescent. The mean energy‐transfer time is 7 ± 2 ps at room temperature. The dominant mechanism for the energy‐transfer process is Dexter‐type electron exchange, with Förster‐type dipole–dipole interactions accounting for less than 10 % of the total transfer probability. There are no indications for light‐induced electron transfer in this system, although there is evidence for a nonradiative decay channel not normally seen for F‐type BODIPY dyes. This new escape route is further exposed by the application of high pressure. The meso‐pyridine group is a passive bystander until protons are added to the system. Then, protonation of the pyridine N atom leads to complete extinction of fluorescence from the BODIPY dye and slight recovery of fluorescence from the perylene units. Quenching of BODIPY‐based fluorescence is due to charge‐transfer to the pyridinium unit whereas the re‐appearance of perylene‐based emission is caused by a reduction in the Förster overlap integral upon protonation. Other cations, most notably zinc(II) ions, bind to the pyridine N‐atom and induce similar effects but the resultant conjugate is weakly fluorescent.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)