Nanoparticle‐Mediated Intervalence Charge Transfer: Core‐Size Effects

Abstract

Two types of platinum nanoparticles (NPs) functionalized with ethynylferrocene were prepared. The subnanometer-sized NPs (Pt10eFc) showed semiconductor-like characteristics with a bandgap of about 1.0 eV, and the other was metal-like with a core size of about 2 nm (Pt314eFc) and no significant bandgap. IR spectroscopic measurements showed a clear red-shift of the C≡C and ferrocenyl ring =C-H vibrational energies with increasing particle core size owing to enhanced intraparticle charge delocalization between the particle-bound ferrocenyl moieties. Electrochemical measurements showed two pairs of voltammetric peaks owing to intervalence charge transfer between the ferrocenyl groups on the nanoparticle surface, which was apparently weaker with Pt10 eFc than with Pt314 eFc. Significantly, the former might be markedly enhanced with UV photoirradiation owing to enhanced nanoparticle electronic conductivity, whereas no apparent effects were observed with the latter.

Photo-Gated Intervalence Charge Transfer of Ethynylferrocene Functionalized Titanium Dioxide Nanoparticles

“…Specifically, because of the apparent bandgap, the low electrical conductivity of semiconductor nanoparticles in the dark would diminish the electronic communication between the particle-bound functional moieties; whereas under photoirradiation with photon energy greater than the nanoparticle bandgap, the enhanced electrical conductivity is anticipated to facilitate intraparticle charge transfer. This photo-gating effects have indeed been observed in recent studies with semiconducting Pt 10 nanoclusters [12] and silicon nanoparticles [21]. Yet, in these earlier studies [12,21], the nanoparticle-mediated IVCT remained very weak even under photoirradiation, where the resulting nanoparticles behaved analogously to a Class I/II compound, as manifested in spectroscopic and electrochemical measurements.…”

“…This photo-gating effects have indeed been observed in recent studies with semiconducting Pt 10 nanoclusters [12] and silicon nanoparticles [21]. Yet, in these earlier studies [12,21], the nanoparticle-mediated IVCT remained very weak even under photoirradiation, where the resulting nanoparticles behaved analogously to a Class I/II compound, as manifested in spectroscopic and electrochemical measurements. This is the primary motivation of the present study where we used ethynylferrocene functionalized titanium dioxide (TiO 2 -eFc) nanoparticles as the illustrating example to demonstrate that with a proper alignment of the photon energy and the nanoparticle bandgap energy, nanoparticle-mediated IVCT may be enhanced significantly.…”

“…The successful incorporation of the eFc ligands onto the TiO 2 nanoparticle surface was confirmed by 1 H NMR and FTIR spectroscopic measurements. [12,23,24]. The fact that no sharp features were observed, along with the absence of alkynyl (≡CH) protons at 2.7 ppm, suggests that the nanoparticles were spectroscopically clean and free of monomeric eFc ligands [25].…”

“…Based on the degree of intramolecular charge delocalization, the mixed valence species are generally categorized as Class I, II or III compounds, as suggested by Robin and Day [8][9][10]. Recently, it has been found that IVCT may also be achieved with metal nanoparticles whereby functional moieties are bound onto the nanoparticle surface through conjugated metal-ligand interfacial bonds and the metallic nanoparticle cores act as conducting spacers to facilitate intraparticle charge delocalization [11][12][13]. Experimentally, a variety of conjugated metal-ligand interfacial bonds have recently been formed for nanoparticle surface functionalization.…”

Identification of the formation of metal–vinylidene interfacial bonds of alkyne-capped platinum nanoparticles by isotopic labeling

“…HC12 or DC12-functionalized platinum nanoparticles (PtHC12 or PtDC12) were then prepared by carbon monoxide reduction of PtCl 4 in the presence of HC12 or DC12. 12,13 The synthetic details were included in the ESI.†…”