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Cross-Coupled Phenyl- and Alkynyl-Based Phenanthrolines and Their Effect on the Photophysical and Electrochemical Properties of Heteroleptic Cu(I) Photosensitizers

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journal contribution
posted on 25.03.2021, 12:36 by Florian Doettinger, Yingya Yang, Marie-Ann Schmid, Wolfgang Frey, Michael Karnahl, Stefanie Tschierlei
With the aims of increasing the antenna system and improving the photophysical properties of Cu­(I)-based photosensitizers, the backbone of 2,9-dimethyl-1,10-phenanthroline was selectively extended in the 5,6-position. Applying specifically tailored Suzuki–Miyaura and “chemistry-on-the-complex” Sonogashira cross-coupling reactions enabled the development of two sets of structurally related diimine ligands with a broad variety of different phenyl- and alkynyl-based substituents. The resulting 11 novel heteroleptic Cu­(I) complexes, including five solid-state structures, were studied with respect to their structure–property relationships. Both sets of substituents are able to red-shift the absorption maxima and to increase the absorptivity. For the alkynyl-based complexes, this is accompanied by a significant anodic shift of the reduction potentials. The phenyl-based substituents strongly influence the emission wavelength and quantum yield of the resulting Cu­(I) complexes and lead to an increase in the emission lifetime of up to 504 ns, which clearly indicates competition with the benchmark system [(xantphos)­Cu­(bathocuproine)]­PF6.

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