C-H Borylation/Cross-Coupling Forms Twisted Donor-Acceptor Compounds Exhibiting Donor-Dependent Delayed Emission

Benzothiadiazole (BT) directed C-H borylation using BCl₃ , followed by B-Cl hydrolysis and Suzuki-Miyaura cross-coupling enables facile access to twisted donor-acceptor compounds. A subsequent second C-H borylation step provides, on arylation of boron, access to borylated highly twisted D-A compounds with a reduced bandgap, or on B-Cl hydrolysis/cross-coupling to twisted D-A-D compounds. Photophysical studies revealed that in this series there is long lifetime emission only when the donor is triphenylamine. Computational studies indicated that the key factor in observing the donor dependent long lifetime emission is the energy gap between the S₁ /T₂ excited states, which are predominantly intramolecular charge-transfer states, and the T₁ excited state, which is predominantly a local excited state on the BT acceptor moiety.