Pyrene fluorescence in 2,7-di(4-phenylethynyl)pyrene-bridged bis(alkenylruthenium) complexes

Complexes PyrDPE-RuCl and PyrDPE-Ruacac with a pi-extended 2,7-di(4-phenylethynyl)pyrene linker undergo simultaneous one-electron oxidations of their {Ru}-styryl entities. The absence of an intervalence charge-transfer (IVCT) band at intermediate stages, where the mixed-valent, singly oxidized radical cation is present, and spin density confinement to the terminal styryl ruthenium site(s) are tokens of a lack of electronic coupling between the {Ru} entities across the pi-conjugated linker. The close similarity of the linker-based pi -> pi* bands in the complexes and the free ligand and their insensitivity towards oxidations at the terminal sites indicate that the central pyrenyl fluorophore is electronically decoupled from the electron-rich {Ru}-styryl termini. As a consequence, the complexes offer stable pyrene-based fluorescence emissions at 77 K, which are red-shifted from that of the linker. The large pi-extended 2,7-di(1-vinyl-4-ethynylphenyl)pyrene-linker mutually insulates the terminally appended ruthenium moieties and electronically decouples them from the pyrene fluorophore, resulting in stable pyrene emission at 77 K.

Automated summary

Through the study of complexes, it is found that complexes with π-conjugated linkers can effectively decouple electrons, thus stabilizing fluorescence emission.