Novel benzo[1,2-d:4,5-d']bis([1,2,3]thiadiazole) electron-withdrawing building block for the design of materials with tunable photophysical properties and highly efficient luminescence.

Symmetric and asymmetric D-AD' derivatives based on the benzo[1,2-d:4,5-d']bis([1,2,3]thiadiazole) moiety with different donor groups were synthesized. Symmetric dyes were prepared from benzo[1,2-d:4,5-d']bis([1,2,3]thiadiazole) by palladium catalyzed CH (het)arylation reaction. Asymmetric molecules were synthesized from 4-bromobenzo[1,2-d:4,5-d']bis([1,2,3]thiadiazole) by two consecutive cross-coupling reactions: direct CH (het)arylation and Suzuki-Miyaura reaction. Symmetric molecules were shown to exhibit higher emission quantum yields (up to 86%) compared to their asymmetric counterparts due to dual excitation pathways. Time-resolved fluorescence studies revealed two emitting excited states for symmetric 4,8-di(thiophen-2-yl)benzo[1,2-d:4,5-d']bis([1,2,3]thiadiazole): intramolecular charge transfer and locally excited states. The photoluminescence efficiency of symmetric dyes exhibits a weak dependence on the solvent nature, maintaining high values in both polar and low-polar environments. The obtained data correlate well with the results of quantum chemical calculations. Thus, symmetric D-A-D molecules based on [benzo[1,2-d:4,5-d']bis([1,2,3]thiadiazole) may be useful in the design of promising highly luminescent materials.