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

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 ( b romine– l ithium e xchange– b orylation– S uzuki) 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 , R 2 = 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.