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Triplet Excimer Emission in a Series of 4,4′-Bis(N-carbazolyl)-2,2′-biphenyl Derivatives

Title data

Hoffmann, Sebastian T. ; Schrögel, Pamela ; Rothmann, Michael ; Albuquerque, Rodrigo Q. ; Strohriegl, Peter ; Köhler, Anna:
Triplet Excimer Emission in a Series of 4,4′-Bis(N-carbazolyl)-2,2′-biphenyl Derivatives.
In: The Journal of Physical Chemistry B. Vol. 115 (2011) Issue 3 . - pp. 414-421.
ISSN 1520-5207
DOI: https://doi.org/10.1021/jp107408e

Official URL: Volltext

Abstract in another language

Carbazole-based materials such as 4,4′-bis(N-carbazolyl)-2,2′-biphenyl (CBP) and its derivatives are frequently used as matrix materials for phosphorescent emitters in organic light emitting diodes (OLED)s. An essential requirement for such matrix materials is a high energy of their first triplet excited state. Here we present a detailed spectroscopic investigation supported by density functional theory (DFT) calculations on two series of CBP derivatives, where CH3 and CF3 substituents on the 2- and 2′-position of the biphenyl introduce strong torsion into the molecular structure. We find that the resulting poor coupling between the two halves of the molecules leads to an electronic structure similar to that of N-phenyl-3,6-dimethylcarbazole, with a high triplet-state energy of 2.95 eV. However, we also observe a triplet excimer emission centered at about 2.5−2.6 eV in all compounds. We associate this triplet excimer with a sandwich geometry of neighboring carbazole moieties. For compounds with the more polar CF3 substituents, the lifetime of the intermolecular triplet excited state extends into the millisecond range for neat films at room temperature. We attribute this to an increased charge-transfer character of the intermolecular excited state for the more polar substituents.

Further data

Item Type: Article in a journal
Refereed: Yes
Institutions of the University: Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics > Lehrstuhl Experimentalphysik II - Optoelektronik weicher Materie > Lehrstuhl Experimentalphysik II - Optoelektronik weicher Materie - Univ.-Prof. Dr. Anna Köhler
Faculties
Faculties > Faculty of Mathematics, Physics und Computer Science
Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics
Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics > Lehrstuhl Experimentalphysik II - Optoelektronik weicher Materie
Result of work at the UBT: Yes
DDC Subjects: 500 Science > 530 Physics
Date Deposited: 13 Feb 2015 12:23
Last Modified: 15 May 2015 08:48
URI: https://eref.uni-bayreuth.de/id/eprint/6727