10.1002/anie.202014138
Angewandte Chemie International Edition
RESEARCH ARTICLE
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and triaryl TA. Configurational stability of angularly fused H1 was
obtained without any additional blocking groups at the terminal
positions. Configurationally flexible H2 is a new type of building
block consisting of both angularly and linearly fused rings. H1
feature moderate (high among helicenes) fluorescence quantum
yields and superior chiroptical properties with |gabs| of up to 1.12
× 10−2. Excellent Φfl of 43-47% were recorded in CH2Cl2 solution
for H2. Intense fluorescence (Φfl. of up to 25%) was retained in
the solid state for H1-Me2, H1-Ph2, and H2-Ph4 affording green,
yellow, and blue emitters, respectively. Thus, introduction of
boron into helical scaffolds provided helicenes with outstanding
optical properties both in solution and in the solid state. These
features along with high chemical and photostability make these
fluorophores attractive for application as pristine materials or
(chiral) emissive dopants in polymer matrices in OLEDs,
fluorescent solid-state sensors and fluorescent probes for
bioimaging.
The flexibility of our synthetic approach opens up the
opportunity to prepare heterohelices with precisely modulated
properties. Incorporation of both types of units should facilitate
modification of their helical pitch, the extent of the intersystem
crossing and optical properties. Our current efforts are focused on
the application of this concept to the synthesis of extended
systems.
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Acknowledgements
The authors are grateful for financial support from the Keck-
Köppe Foundation and Universitätsbund Würzburg (AZ 18-32),
Fonds der Chemischen Industrie (SK 204/03), and the German
Research Foundation (DFG) for the Emmy-Noether fellowship
(NO 1459/1-1). A. N.-K. would like to thank Prof. Frank Würthner
for his support in the past years, mentorship and many insightful
discussions. We thank Dr. Matthias Stolte for practical advice
regarding the measurements of solid-state emission.
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Keywords: chirality • circular dichroism • helicene • organoboron
• fluorescence
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