Intriguing Role of Weak Electron Donor in Dictating the Luminescent Characteristics of D^S‐A‐D^W Materials

Abstract The short wavelength (SW) emission region of the materials employing strong donor (D^S) phenothiazine (PTZ) is generally correlated to its quasi‐axial (QA_PTZ) conformer arrangement. This propels to investigate the specific role of weak donors (D^W) such as carbazole (CZ) in determining the emission characteristics of molecular heredity (MH) type structural design encompassing dual donors of varying strength. For this purpose, a common D^S(PTZ)–Acceptor unit is linked to the D^W(CZ) unit via different linkage positions to form M1, M2, and M3, which not only alters the absorption and dual emission characteristics but also influences the delayed fluorescence phenomenon. The SW emission originates by minimizing the aggregation factor rather than by literature envisaged QA_PTZ conformer. Incorporating M1 as a single molecular white light emitter (SMWLE) in near UV light emitting diode (LED) devices results in cold white light emission with CRI of 68 and CIE of (0.24, 0.33), while its corresponding solution‐processed organic light‐emitting diode devices delivers warm white electroluminescence with an EQE of 5.8%. Overall, this work demonstrates the significant contribution of the D^W in attaining the white light emission characteristics of MH molecular design not only at the molecular level but also in practical light‐emitting devices.