Phthalocyaninato complexes with peripheral alkylthio chains: Disk-like adsorbate species for the vertical anchoring of ligands onto gold surfaces

Abstract

Thin metalorganic films were prepared on gold by self-assembly of thioether-functionalised phthalocyaninato complexes from solution. The phthalocyaninato ligands used contain eight peripheral, β-positioned, alkylthio substituents SR (1a: R = n-C8H17, 1b: R = n-C12H25), which serve as headgroups for surface binding and promote lateral assembly, while the disk-like phthalocyaninato core offers the scope for the attachment of axial ligands to the adsorbed molecules. This process was mimicked by coordination of pyridine (Py) to [Zn(1a)] and [Zn(1b)], respectively. The crystal structures of the products [Zn(1a)(Py)] and [Zn(1b)(Py)] were determined. The crystal structures of 4,5-bis(octylthio)phthalodinitrile and 4,5-bis(dodecylthio)phthalodinitrile were also determined. The films fabricated from [Mn(1a)Cl] and [Mn(1b)Cl] on gold were characterised by XPS, ToF-SIMS and NEXAFS spectroscopy, which revealed the presence of well-defined and homogeneous self-assembled monolayers (SAMs), whose constituents are bound to the substrate by thioether–gold linkages. The orientation of the macrocycles is predominantly parallel to the surface. Strong electronic interaction of the manganese(III) centre with the substrate leads to Cl loss upon adsorption and its reduction to MnII.

Surface chemistry of porphyrins and phthalocyanines

“…Siemeling et al adsorbed various phthalocyanines with 8 alkylthio substituents on Au(1 1 1). In the case of the (Cl)Mn complexes, the strong electronic interaction of the Mn(III) centers with the Au substrate resulted in a loss of Cl and reduction to Mn(II) [458] (cf. Section 7.…”

Molecular Suction Pads: Self‐Assembled Monolayers of Subphthalocyaninatoboron Complexes on Gold

“…Equivalently substituted phthalocyaninato manganese complexes bind exclusively coordinatively, [5b] whereas less stable subphthalocyaninatoboron molecules also showed thiolate-type sulfur atoms to a certain extent. [4] In addition, both binding situations were observed for diphthalocyaninatoterbium complexes on gold.…”

“…We, and others, have used oligodentate binding units for multipoint attachment to prepare self-assembled monolayers (SAMs) on gold. We have studied a range of SAMs based on adsorbate molecules with two, [2] three, [3] four, [2] six [4] and eight [5] thioether binding units.…”

“…Such disc-like units provide a versatile platform for the surface immobilisation of sterically demanding functional groups. [4,5] Subphthalocyaninatoboron complexes are the lower homologues of the ubiquitous phthalocyanine derivatives. They are composed of only three isoindoline units, dome-shaped and exclusively available with a boron(III) ion in the central cavity.…”

SHG studies of self-assembled monolayers of subphthalocyanines on gold

“…Thus, molecules with a rigid spacer unit and a big footprint with multiple anchor groups, for example phthalocyaninato and subphthalocyaninato complexes, are very promising for the preparation of stable monolayers. The different geometry of these molecules doesn't allow diving of functional groups and provides relatively large space for the functional groups, which are the main requirements for preparation of smart surfaces [13]. Moreover, phthalocyaninato and subphthalocyaninato complexes exhibit outstanding chemical and physical properties, which make them ideal candidates for SAM preparation.…”