Isonitrile-functionalized ruthenium nanoparticles: intraparticle charge delocalization through Ru=C=N interfacial bonds

Ruthenium nanoparticles (2.06 ± 0.46 nm in diameter) stabilized by 1-hexyl-4-isocyanobenzene (CNBH), denoted as RuCNBH, were prepared by the self-assembly of isonitrile molecules onto the surface of “bare” Ru colloids by virtue of the formation of Ru=C=N− interfacial bonds. FTIR measurements showed that the stretching vibration of the terminal −N≡C bonds at 2119 cm−1 for the monomeric ligands disappeared and concurrently three new bands at 2115, 2043, and 1944 cm−1 emerged with RuCNBH nanoparticles, which was ascribed to the transformation of −N≡C to Ru=C=N− by back donation of Ru-d electrons to the π* orbital of the organic ligands. Metathesis reaction of RuCNBH with vinyl derivatives further corroborated the nature of the Ru=C interfacial bonds. When 1-isocyanopyrene (CNPy) was bounded onto the Ru nanoparticles surface through Ru=C=N interfacial bond (denoted as RuCNPy), the emission maximum was found to red-shift by 27 nm, as compared to that of the CNPy monomers, along with a reduced fluorescence lifetime, due to intraparticle charge delocalization that arose from the conjugated Ru=C=N− interfacial bonds. The results of this study further underline the significance of metal−organic interfacial bonds in the control of intraparticle charge-transfer dynamics and the optical and electronic properties of metal nanoparticles.