Red-NIR luminescence of Mo6 monolayered assembly directly anchored on Au(001)

Abstract

A tailored near infrared luminescent Mo₆ octahedral cluster bearing thiocyanate (NCS) terminal ligands, [Mo₆Brⁱ₈(NCS)^a₆]²⁻, has been synthesized to anchor onto a gold substrate. After immobilization, [Mo₆Brⁱ₈(NCS)^a₆]²⁻ building blocks form a self-assembled monolayer on the Au(001) surface as shown by scanning tunneling microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. Strikingly, the photoluminescence of [Mo₆Brⁱ₈(NCS)^a₆]²⁻ observed in the powder precursor remains after grafting on Au(001). No quenching effect was observed despite the vicinity of the flat metal surface unlike most of the molecular luminophors. Periodic and molecular computational investigations based on density functional theory show that optical properties originate from the Mo₆Brⁱ₈ core and are protected by the NCS outer sphere, despite the shortness of the anchors.