From White to Red: Electric-Field Dependent Chromaticity of Light-Emitting Electrochemical Cells based on Archetypal Porphyrins

Michael D. Weber, Judith E. Wittmann, Alexandra Burger, Osman Barış Malcıoğlu, Javier Segarra-Martí, Andreas Hirsch, Pedro B. Coto, Michel Bockstedte, Rubén D. Costa

Research output: Contribution to journalArticlepeer-review

40 Citations (Scopus)

Abstract

The differences in the electroluminescence (EL) of red-emitting free-base (H2TPP) and Zn-metalated (ZnTPP) archetypal porphyrins are rationalized in light-emitting electrochemical cells by means of an electric-field dependent effect, leading to whitish and reddish devices, respectively. Although H2TPP shows superior electrochemical and photophysical features compared to ZnTPP, devices prepared with ZnTPP surprisingly stand out with a deep-red EL similar to its photoluminescence (PL), while H2TPP devices feature unexpected whitish EL. Standard arguments such as degradation, device architecture, device mechanism, and changes in the nature of the emitting excited states are discarded. Based on electrochemical impedance spectroscopy and first-principles electronic structure methods, we provide evidence that the EL originates from two H2TPP regioisomers, in which the inner ring H atoms are placed in collinear and vicinal configurations. The combination of their optical features provides an explanation for both the high- and low-energy EL features. Here, the emitting excited state nature is ascribed to the Q bands, since the Soret excited states remain high in energy. This contrasts to what is traditionally postulated in reports focused on H2TPP lighting devices. Hence, this work provides a new explanation for the nature of the high-energy EL band of H2TPP that might inspire future works focused on white-emitting molecular-based devices.

Original languageEnglish
Pages (from-to)6737-6750
Number of pages14
JournalAdvanced Functional Materials
Volume26
Issue number37
DOIs
Publication statusPublished - 2016 Oct 4
Externally publishedYes

Keywords

  • collinear and vicinal regioisomers
  • electric-field dependent chromaticity
  • light-emitting electrochemical cells
  • tetraphenyl porphyrin
  • thin-film white-emitting sources

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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