Soliton pair charge storage in doped polyene molecules: Evidence from photoelectron spectroscopy studies

Abstract

The ^-electronic structural changes in a polyene molecule containing seven double bonds, a,codiphenyltetradecaheptaene (DP7), have been studied upon gradually doping with sodium, using x-ray and ultraviolet photoelectron spectroscopies. The spectra are interpreted with the help of detailed quantum chemical calculations. Analysis of the evolution of the XPS and UPS spectra as a function of doping with sodium indicates that the extra charges are stored in the form of two charged solitons on the polyene part of the molecules, which results in two new energy levels in the originally forbidden energy gap.

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].…”

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

“…We have already noted that the alkali-metal states have been attributed to lower Hubbard bands, 6 bipolaron states, 2,5 or a solitonantisoliton pair. 3,4 While the models are not necessarily mutually exclusive, a model cannot be generally applicable unless it applies in all of the above molecular host systems ͑or at least most͒. Insight into the most applicable model can be, in part, gained through an inspection of the temperature dependence of the sodium induced states in the HOMO-LUMO gap, as indicated in the Introduction.…”

“…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.…”