Novel Germoles and Their Ladder-Type Derivatives: Modular Synthesis, Luminescence Tuning, and Electroluminescence

Abstract

Considerable effort has been devoted to the design of silicon-containing π-conjugated materials for application in optoelectronic devices and fluorescent bioimaging. However, the synthesis and spectroscopic tuning of germanium (Ge)-conjugated systems are challenging because of the paucity of synthetically useful methods. Herein, we report a simple and effective method of lithium naphthalenide-induced intramolecular cyclization to construct architecturally diverse Ge-containing π-conjugated molecules, including benzogermoles and their ladder-type derivatives, with high yields of up to 92%. The photophysical properties of these molecules can be finely controlled by the introduction of electron-donating or -withdrawing substituents, and intense luminescence ranging from deep-blue to red regions in the solid state was observed. A quantitative model based on the Hammett constant against the luminescence wavelength showed a good linear correlation, allowing us to reliably predict and design luminescent materials with specific properties for applications. Notably, Ge-bridged ladder-type derivatives exhibited high photoluminescence and efficient deep-blue electroluminescence with good color purity. We believe this study will open a new avenue to organogermanium chemistry and offers greater flexibility for electronic structural tuning.