Reactions of low work function metals Na, Al, and Ca on α,ω-diphenyltetradecaheptaene. Implications for metal/polymer interfaces

Abstract

The interactions between different low work function metals aluminium, calcium and sodium, and α,ω-diphenyltetradecaheptaene, a model molecule for certain conjugated polymers, have been investigated using both x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The spectra are interpreted with the help of the results of quantum chemical calculations performed within the local spin density (LSD) approximation methodology. The metals are found to interact with the conjugated system in very different ways. Aluminium forms a covalent bond, which strongly modifies the π-electronic structure of the conjugated molecule, while both the sodium and the calcium atoms act as doping agents, inducing new states in the otherwise forbidden bandgap. These new gap states can be viewed as a soliton–antisoliton pair for the Na/DP7 and a bipolaronic-like defect for Ca/DP7.

The coadsorption and interaction of molecular icosahedra with mercury

“…The evidence for metallic mercury, from the Hg 5d 5/2 core level widths does not suggest that mercury atoms may form a lattice which weakly interacts with orthocarborane lattice, or Hg may form a wetting surfactant layer and a layer between the Cu substrate and orthocarborane molecular fi lm which would easily explain a uniform shift in the molecular orbital photoemission binding energies. In this regard, Hg is very different from the more homo geneous mixtures formed with some metals and molecularly chemisorbed species [14][15][16][38][39][40][41][42][43][44][45][46][47][48][49].…”

Modeling Photoelectron Spectra of Conjugated Oligomers with Time-Dependent Density Functional Theory

“…Therefore, UPS is used to investigate the band structures of doped forms of conducting organic oligomers and polymers. [5][6][7][8][9] Theoretically UPS can be simulated via the one-electron approximation by employing band structure calculations and investigating the density of states (DOS). For obtaining energies of cations from band structure calculations, Koopmans's theorem 10 must hold, which is strictly speaking only true for HartreeFock (HF) and semiempirical wave functions as correlated wave functions do not provide one-electron energy levels and the meaning of orbital energies apart from that of the highest occupied molecular orbital (HOMO), is controversial in density functional theory (DFT).…”

Evidence of dynamic Jahn-Teller distortions in two-dimensional crystalline molecular films

“…6 These alkali induced states have been variously ascribed to the formation of lower Hubbard bands, 6 bipolaron states, 5,2 and a soliton-antisoliton pair. 3,4 The observation of two photoemission states, in place of a single molecular orbital, can be a consequence of either the photoemission initial state or final state ͑or indeed have contributions from both͒. Such multiplication of the expected number of photoemission features is a known result of symmetry breaking in the photoemission process 7 and other final state effects.…”

“…1 In fact there are many examples where alkali doping creates states below the Fermi level ͑the occupied side͒, but within the host material ͑the undoped material͒ band gap, i.e., between the highest occupied molecular orbital ͑HOMO͒ and the lowest unoccupied molecular orbital ͑LUMO͒ of the undoped system. The appearance of states in the HOMO-LUMO gap has been reported for alkali doping of poly͑para-phenylenevinylene͒, 2 ␣, -diphyltetradecaheptaene, 3,4 poly͑pyridine-2,5-diyl͒, 5 poly͑2,2Ј-bipyridine-5,5Ј-diyl͒ ͑Ref. 5͒ and 1,2-dicarbadodecaborane.…”

“…Such multiplication of the expected number of photoemission features is a known result of symmetry breaking in the photoemission process 7 and other final state effects. Initial state effects such as a soliton-antisoliton pairs or bipolaron formation [2][3][4][5] have also been invoked, but such initial-state effects, as well as final-state effects, are generally unlikely to exhibit substantial temperature dependence and certainly these effects are unlikely to become more pronounced in photoemission with increased temperature ͑quite the opposite is generally expected͒. For solitonantisoliton pairs, static Jahn-Teller distortions, bipolaron formation or symmetry breaking in the spectroscopy final state, increasing temperature should lead to a decrease in the ability to resolve the two photoemission states as with increasing temperature the polarons should unbind and broadening effects due to dynamic motion should play an increasing role.…”