Bis(carbazolyl) derivatives of pyrene and tetrahydropyrene: synthesis, structures, optical properties, electrochemistry, and electroluminescence

Bilal R Kaafarani,Brigitte Wex,Alexandr Fonari,Ala'A O El-Ballouli,Roman Trattnig,Rony S Khnayzer,Emil J W List,Stefan Sax,Stephen Barlow,Jean-Luc Brédas,Chad Risko,Digambara Patra,Tatiana V Timofeeva,Seth R Marder

doi:10.1039/c2tc00474g

Abstract

Tetrahydropyrene and pyrene have been functionalized in their 2,7-positions with carbazole and 3,6-di-tert-butylcarbazole groups, and the properties of these new compounds are compared to analogous carbazole and 3,6-di-tert-butylcarbazole derivatives of benzene and biphenyl using X-ray crystallography, UV-vis absorption and fluorescence spectroscopy, electrochemistry, and quantum-chemical calculations. The absorption spectra are similar to those of their biphenyl-bridged analogues, although TD-DFT calculations indicate a different description of the excited states in the pyrene case, with the lowest observed absorption no longer corresponding to the S0 → S1 transition. The 3,6-di-tert-butylcarbazole compounds show reversible electrochemical oxidations; the benzene, biphenyl, tetrahydropyrene, or pyrene bridging groups have little impact on the first oxidation potential. Bilayer organic light-emitting diodes incorporating the tetrahydropyrene and pyrene derivatives as emitters show deep-blue electroluminescence.

Highlights

Organic electroluminescent devices are of interest for use in at panel displays and for lighting.[1,2,3] Full-color displays require the use of red, green, and blue emitters; relative to red and green emitters, blue emitters are not as well optimized in terms of their efficiency, color purity, and stability.[4,5,6,7] Efficient charge injection from electrodes into the adjacent organic layers, balanced charge transport, con nement of hole–electron recombination and the resultant excitons in the desiredPolyaromatic molecules, such as diphenylanthracene,[9] have been studied as potential uorescent blue emitters
On top of the ITOsubstrates a layer of PEDOT:PSS was applied via spin-coating under ambient conditions and dried under dynamic vacuum according to the speci cations
Synthesis Compounds 1–4 were synthesized from Ullmann or Buchwald– Hartwig coupling of the appropriate carbazole to the dibromo/ diiodo derivatives of the bridging groups

Summary

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Bis(carbazolyl) derivatives of pyrene and tetrahydropyrene: synthesis, structures, optical properties, electrochemistry, and electroluminescence†. Tetrahydropyrene and pyrene have been functionalized in their 2,7-positions with carbazole and 3,6-ditert-butylcarbazole groups, and the properties of these new compounds are compared to analogous carbazole and 3,6-di-tert-butylcarbazole derivatives of benzene and biphenyl using X-ray crystallography, UV-vis absorption and fluorescence spectroscopy, electrochemistry, and quantumchemical calculations. The absorption spectra are similar to those of their biphenyl-bridged analogues, TD-DFT calculations indicate a different description of the excited states in the pyrene case, with the lowest observed absorption no longer corresponding to the S0 / S1 transition. The 3,6-di-tertbutylcarbazole compounds show reversible electrochemical oxidations; the benzene, biphenyl, tetrahydropyrene, or pyrene bridging groups have little impact on the first oxidation potential. Bilayer organic light-emitting diodes incorporating the tetrahydropyrene and pyrene derivatives as emitters show deep-blue electroluminescence

Introduction

Photophysical studies

Results and discussion

Crystal and molecular structures

Conclusion