Palladium Complexes of Perylene Diimides:  Strong Fluorescence Despite Direct Attachment of Late Transition Metals to Organic Dyes

Abstract

We prepared the first sigma-bonded metal complexes of widely utilized organic dyes, perylene tetracarboxylic acid diimides (PDIs). These 1,7-dipalladium PDI complexes were synthesized by C-Br oxidative addition of 1,7-dibromo-N,N'-dicyclohexyl PDI (Br2PDI) to Pd(0) phosphine complexes bearing triphenylphosphine and bischelating 1,2-bis(diphenylphosphino)ethane (dppe). The structures of Pd-PDI complexes were elucidated by single-crystal X-ray analysis. Surprisingly, despite direct attachement of two late transition metal centers, Pd-PDI systems are highly fluorescent (Phi=0.65 and 0.22 for triphenylphosphine and dppe systems, respectively). This is rationalized in terms of weak electronic interactions between the metal centers and PDI pi-system, as revealed by TD-DFT calculations.

Ultrafast photodriven intramolecular electron transfer from an iridium-based water-oxidation catalyst to perylene diimide derivatives

“…S2) show a population of PDI triplet at long times, with a yield of approximately 8% (14,20). The yield is smaller in CH 2 Cl 2 -a modest 2%-which is reasonable in the context of electron transfer theory given that the ion-pair energy lies higher than the PDI triplet energy in toluene than it does in CH 2 Cl 2 .…”

“…The design of a lightdriven water-splitting system based on molecular catalysts requires a fundamental understanding of the individual electron transfer steps involved in multielectron catalyst activation. To investigate the energetic and kinetic demands of coupling photodriven charge separation and catalysis, many research groups have studied the photophysical properties of covalently linked redox-active organic dyes and transition metal complexes (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). In several cases, electron transfer to or from the metal has been observed and characterized, though energy transfer and intersystem crossing to the chromophore triplet state can be significant competing processes.…”

“…Nevertheless, the competitiveness of heavy atom-induced SO-ISC is a concern for PDI/metal complex assemblies, and previous studies by the Castellano group of PDI linked to platinum(II) metal centers through acetylide groups at its 1-position have reported SO-ISC from 1Ã PDI to 3Ã PDI in 2-4 ps (7,12). However, when Pd(II) is directly attached to the PDI aromatic core through metal-carbon σ-bonds, strong PDI fluorescence is observed and the yield of 3Ã PDI is estimated to be only 6%, which is explained by the relatively weak coupling between the metal-based orbitals and the frontier π-orbitals of PDI (14). Also, Pd(II)-PDI and Pt(II)-PDI complexes in which the metal centers are bound through pyridyl groups at the PDI imide positions-through which the PDI frontier orbitals each have a nodal plane-have fluorescence quantum yields of 86% and 88%, respectively (15).…”

Metal Complexes of a Boron‐Dipyrromethene (BODIPY)‐Tagged N‐Heterocyclic Carbene (NHC) as Luminescent Carbon Monoxide Chemodosimeters

“…[20] Another prominent quenching mechanism is photoinduced electron transfer (PET). Based on this, a change in the electron density at the transition-metal center should lead to different brightness.…”

The Synthesis of Azaperylene-9,10-dicarboximides

“…Previous attempts to directly attach late transition metals to the perylene skeleton resulted in minimal electronic interaction between the metal center and PDI π-system. 8 Moreover, it was found that introducing conjugated spacers between the metal center and PDI π-system only yielded non-emissive complexes. 7 Inspired by the superior photophysical properties and high phosphorescence quantum yields of cyclometalated platinum (II), and ruthenium (II) iridium (III) complexes, 9 we sought to synthesize PDI or PI analogs that contained a 2-phenylpyridine moiety that would eventually allow access to cyclometalated perylene complexes.…”