Modular One-Pot Access to π-Expanded Tetrakis(Phenothiazinyl)-Silanes With Broadly Tunable Redox and Emission...

The development of multichromophoric materials with independently tunable redox and emissive properties remains a central challenge in organic materials chemistry. Herein, we report a library of 21 predominantly C3-connected tetrakis(phenothiazinyl)silanes, accessed principally via a modular one-pot BLEBS (bromine-lithium exchange-borylation-Suzuki) strategy in moderate to very good yields (15%-87%), featuring systematic variation at the 10-, 7- and 2-positions of the phenothiazine scaffold, a C1-connected regioisomeric reference, as well as four distinct linker architectures. Cyclic voltammetry reveals fully reversible first oxidations spanning +0.17 to +0.42 V versus Fc/Fc⁺, with a linear Hammett correlation (σ_p, R² = 0.985) for the 7-substituted subset confirming predictable electronic fine-tuning. Photophysically, the tetramers exhibit bright fluorescence with quantum yields up to Φ_F = 0.90 and emission tunable from deep blue to yellow-green (441-533 nm) through linker engineering. (TD-)DFT calculations confirm locally excited, phenothiazine-centered emissive states and quantitatively reproduce the experimental variation in radiative rates via computed oscillator strengths. Notably, 7-substitution selectively modulates the redox potentials while leaving the optical gap essentially invariant, whereas linker modification primarily governs the emission energy, establishing the tetrakis(phenothiazinyl)silane scaffold as a versatile platform for the largely independent control of electrochemical and photophysical properties.