Designing New Small Molecules from Cyclopentadithiophene (CPDT) Derviatives for Highly Efficient Blue Emitters in OLEDs: DFT Computational Modeling

Novel blue florescent emitters of two types of linear π-conjugated molecules based on the cyclopentadithiophene (CPDT), having the same backbone but bridging positions with C=O (D1) or C=C(CN)2 group (D2) are designed and theoretically studied. Calculations of the molecular properties of the dimers (D1 and D2) were performed in both ground and excited states using the density functional theory (DFT) and its timedependent extension (TD-DFT) at B3LYP functional with 6-311g(d,p) basis set in acetonitrile. The optical properties have been computed and data related to their responses are examined and interpreted. The direct comparison between both dimers highlights the effect of carbonyl ( C=O) bridged groups on emission quenching. In addition, intramolecular charge transfer (ICT) band in the visible region (~672 nm) was detected for D1, in contrast to D2. The ICT is strongly implicated as the quenching emission caused by the electron-donating ( C=O) group for D1. In the three layers based OLED [ITO/NPD/emitting layer (D1 or D2)/Alq3/LiF:Al], the electric responses of the devices were evaluated based on the I-V characteristics. Our theoretical results suggest that the CPDT derivatives have interesting optical properties, which are useful for constructing novel light emitting materials for OLEDs.