Bis(difluoroborylamidinates) with Flexible Ethylene Bridges as Bifunctional Aggregation-Induced Emitters

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPYs) represent one of the most prominent classes of dyes, since they are ubiquitously used in protein and DNA labelling, photodynamic therapies, as luminescent tags, sensors, laser dyes, paint and ink compositions, as well as for electroluminescent devices. [1] This is because of their robustness in terms of photochemical stability, polarity and pH changes of their environment, in particular under physiological conditions. The versatility to introduce multiple functional substituents and ability of BODIPYs to strongly absorb UV-light while providing sharp fluorescence peaks, combined with high quantum yields make these dyes highly attractive for numerous applications. Closely related azaBODIPYs offer an additional N-donor atom in the bora-heterocycle that is susceptible to Lewis acids, which is particularly useful for chemical sensor applications. [2] Despite these manifold advantages, BODIPYs and aza-BODIPYs tend to undergo aggregation-caused quenching (ACQ) through π-stacking that effectively lowers their quantum yields in the solid state. Amidinate ligands with various predominantly aromatic substituents allow the incorporation of an unsymmetrical scaffold for the triaza-BF2 heterocycle which is also substantially bulky and therefore beneficial to promote aggregation-induced emission (AIE) as well as increased Stokes shifts. [3] Our concept features a series of new polydentate bis(amidine) ligands LH2 featuring up to six N-donor atoms and a flexible ethylene bridge. [4] These bis(amidines) and Et2O·BF3 form novel tethered bis(difluoroborylamidinates) [L(BF2)2] that are highly emissive. Herein, we present a series of bis(difluoroborylamidinates) [L1–4 (BF2)2] that serve as efficient blue emitters both in solution (λmax = 398–444 nm) and in the solid state (λmax = 388–398 nm)