Dithienylcyclopentene-functionalised subphthalocyaninatoboron complexes: Photochromism, luminescence modulation and formation of self-assembled monolayers on gold

Abstract

Subphthalocyaninatoboron (SubPc) complexes bearing six peripheral n-dodecylthio substituents and an apical photochromic dithienylperfluorocyclopentene unit were prepared. The photoinduced isomerisation of the apical substitutent from the open to the ring-closed form significantly influences the photoluminescence of the covalently attached SubPc unit, which is more efficiently quenched by the ring-closed form. Films on gold were fabricated from these multifunctional conjugates and characterised by near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS). The results are in accord with the formation of self-assembled monolayers based on dome-shaped SubPc-based anchor groups. Their chemisorption is primarily due to the peripheral n-dodecylthio substituents, giving rise to covalently attached thiolate as well as coordinatively bound thioether units, whose alkyl chains are in an almost parallel orientation to the surface.

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

“…A loss of the axial Cl ligand upon adsorption on gold is highly unlikely, since such a process has never been observed for Cl [8a,8b,8d,11] or other, more extended ligands. [4,9,12] Thirdly, the SAM contains small amounts of oxygen. Oxygen contaminations are commonly observed in oligodentate thioether-based SAMs.…”

“…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. [5a] …”

“…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.…”

“…[4,8b,9] However, the molecular mechanisms by which these binding units interact with gold surfaces and assemble into closed monolayer films when undisturbed by elaborate axial ligands are still unknown. Here we describe the adsorption of two subphthalocyaninatoboron derivatives [BCl{Subpc’(SR) 6 }] (Fig.…”