Tuning of the Singlet-Triplet Energy Gap of Donor-Linker-Acceptor Based Thermally Activated Delayed Fluorescent Emitters.

Thermally activated delayed fluorescent emitters based on carbazole donor, benzonitrile acceptor with the linkers biphenyl, bipyridine and naphthalene are investigated using the density functional theoretical method. The molecule in which bipyridine acts as the linker with the least ΔE is further selected for the designing of a series of D-L-A framework TADF molecules. Remarkably, the ΔE is decreased successively by attaching the additional cyano groups at the acceptor site which is further reduced when the electron donating methoxy groups are attached at the donor site. To know the effect of substituents on ΔE the acceptor moiety of the D-L-A framework is modified with -F, -Cl and -CF substituents. The studies showed a relatively less decrement in the value of ΔE compared to the cyano substituted molecules. However, ΔE significantly reduced further on attaching methoxy groups at the donor site.