The Role of Spacers as a Probe in Variation of Photoluminescence Properties of Mono- and Bi-Nuclear Boron Compounds.

A series of N,O donor-based mono- and binuclear four-coordinated boron complexes were synthesized. Depending on the substitution and spacer, these complexes exhibit intense blue, green and yellow emission in solution states. Notably, the fluorescence quantum yields (Φ_F) and fluorescence decay (lifetime, τ) of mononuclear boron complexes (2 a-2 e) were higher than the binuclear boron complexes (2 f-2 k). The lowest lifetime and quantum yield in binuclear boron complexes were due to intramolecular rotation induced non radiative processes. The disulphide spacer-based boron complexes 2 i-2 k showed aggregation-caused quenching in the THF/H₂O mixture whereas no other complexes were ACQ responsive. These complexes show large Stokes shift, one of them i. e. 2 e has the highest Stokes shift of 130 nm. Further, the electrochemical study suggests the presence of two redox incidences. Theoretical studies show close corroboration between the TD-DFT computed and experimentally measured absorption maxima as well as DFT (GIAO) calculated and experimentally measured ¹¹B NMR values. This complements the appropriate selection of the theoretical methods to shed light on the electronic transitions in the mono- and binuclear BF₂ complexes.