Tuning the Photophysical Properties of BODIPY Molecules by π-Conjugation with Fischer Carbene Complexes

The synthesis, structure, and photophysical properties of novel BODIPY-Fischer alkoxy-, thio-, and aminocarbene dyads are reported. The BODIPY chromophore is directly attached to the carbene ligand by an ethylenic spacer, thus forming donor-bridge-acceptor pi-extended systems. The extension of the pi-conjugation is decisive in the equilibrium geometries of the dyads and is clearly reflected in the corresponding absorption and emission spectra. Whereas the BODIPY fragment is mainly isolated in aminocarbene complexes, it is fully conjugated in alkoxycarbene derivatives. The former thus exhibit the characteristic photophysical properties of BODIPY units, whereas complete suppression of the BODIPY fluorescence emission is observed in the latter, as a direct consequence of the strong electron-accepting character of the (CO)(5)M=C moiety. As the pi-acceptor character of the metal-carbene group can be modified, the electronic properties of the conjugated BODIPY can be tuned. Density functional calculations have been carried out to gain insight into the photophysical properties.