Thiophene-based conjugated polymers are widely applied in organic photoelectronic devices due to their unique optical and electronic properties. Recent research on oligothiophenes as simple models of polythiophenes has demonstrated molecular structural changes from intramolecular torsion along the oligothiophene chain or reaction chemistry that can drastically affect the pi-conjugated electron delocalization along the molecular backbone. Such changes result in a reduction of the effective conjugation length of the oligothiophene, and hence, its conductivity. In this work, sexithiophene (6T) thin film models are subjected to vapor deposition of thin layers of Ag, Al, Mg and Ca, common cathode contact materials, and the resulting interfacial chemistry monitored with surface Raman spectroscopy in ultrahigh vacuum. Metal atoms are estimated to penetrate the 6T films to depths of 2.5 - 5 nm, although interfacial structural changes are induced only by the first 0.5 nm of deposited metal. Intramolecular torsion along individual 6T chains is observed when the contact material is Ag, Al or Mg, causing a change in 6T effective conjugation length. In contrast, reaction chemistry occurs with Ca resulting in the formation of small but observable amounts of amorphous carbon.

Raman spectroscopy of interfacial chemistry between sexithiophene and vapor-deposited low work function metals

248th National Meeting (2014)

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