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Bipolar molecules with high triplet energies: synthesis, photophysical, and structural properties.

Authors
Type
Published Article
Journal
The Journal of Organic Chemistry
1520-6904
Publisher
American Chemical Society
Publication Date
Volume
76
Issue
20
Pages
8300–8310
Identifiers
DOI: 10.1021/jo201488v
PMID: 21950840
Source
Medline

Abstract

This article sheds new light on the interplay of electronic and conformational effects in luminescent bipolar molecules. A series of carbazole/1,3,4-oxadiazole hybrid molecules is described in which the optoelectronic properties are systematically varied by substituent effects which tune the intramolecular torsion angles. The synthesis, photophysical properties, cyclic voltammetric data, X-ray crystal structures, and DFT calculations are presented. Excited state intramolecular charge transfer (ICT) is observed from the donor carbazole/2,7-dimethoxycarbazole to the acceptor phenyl/diphenyloxadiazole moieties. Introducing more bulky substituents onto the diphenyloxadiazole fragment systematically increases the singlet and triplet energy levels (E(S) and E(T)) and blue shifts the absorption and emission bands. The triplet excited state is located mostly on the oxadiazole unit. The introduction of 2,7-dimethoxy substituents onto the carbazole moiety lowers the value of E(S), although E(T) is unaffected, which means that the singlet-triplet gap is reduced (for 7bE(S) - E(T) = 0.61 eV). A strategy has been established for achieving unusually high triplet levels for bipolar molecules (E(T) = 2.64-2.78 eV at 14 K) while at the same time limiting the increase in the singlet energy.

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