Third-Generation W(CNAr)6 Photoreductants (CNAr = Fused-Ring and Alkynyl-Bridged Arylisocyanides)

Homoleptic tungsten(0) arylisocyanides possess photophysical and photochemical properties that rival those of archetypal ruthenium­(II) and iridium­(III) polypyridine complexes. Previous studies established that extending the π-system of 2,6-diisopropylphenylisocyanide (CNDipp) by coupling aryl substituents para to the isocyanide functionality results in W­(CNDippAr)6 oligoarylisocyanide complexes with greatly enhanced metal-to-ligand charge transfer (MLCT) excited-state properties relative to those of W­(CNDipp)6. Extending electronic modifications to delineate additional design principles for this class of photosensitizers, herein we report a series of W­(CNAr)6 compounds with naphthalene-based fused-ring (CN-1-(2- i Pr)-Naph) and CNDipp-based alkynyl-bridged (CNDippCCAr) arylisocyanide ligands. Systematic variation of the secondary aromatic system in the CNDippCCAr platform provides a straightforward method to modulate the photophysical properties of W­(CNDippCCAr)6 complexes, allowing access to an extended range of absorption/luminescence profiles and highly reducing excited states, while maintaining the high molar absorptivity MLCT absorption bands, high photoluminescence quantum yields, and long excited-state lifetimes of previous W­(CNAr)6 complexes. Notably, W­(CN-1-(2- i Pr)-Naph)6 exhibits the longest excited-state lifetime of all W­(CNAr)6 complexes explored thus far, highlighting the potential benefits of utilizing fused-ring arylisocyanide ligands in the construction of tungsten(0) photoreductants.