Evaluating effect of donors and their linking position on photophysical properties of 2-phenylfuro[2,3-b]quinoxaline-based donor-π-acceptor molecules

Two linear D-π-A molecules, pCz-FQ and TPA-FQ, and one folded molecule, oCz-FQ were designed using 2-phenylfuro[2,3-b]quinoxaline (FQ) and carbazole(Cz)/diphenylamine (dPA) as acceptor and donor, respectively, and their photophysical properties were investigated. As donor changed from dPA to Cz, the emission color is blue-shifted, and the S1-T1 energy gap increased from 0.50 eV to 0.73 eV. The theory analysis revealed the T₂-T₁ energy gap could be enlarged to ∼0.89 eV for donor change. As linking mode between the FQ and Cz is changed from para-linkage to ortho-linkage of benzene ring, the T1-S1 spin-orbital coupling value of oCz-FQ is five times improvement.