Theoretical Studies of DCM Derivatives with Dual Electron Donating Group

Novel red emitting bis-condensed DCM derivative with dual homoleptic or heteroleptic electron donating groups (EDG), bis-DCM, bis-DCMOEH and bis-DCMNOEH were designed and their photonic properties were studied theoretically in order to tune the emission wavelength of the deep red region and to enhance the luminescence efficiencies. To gain insight into the factors responsible for the emission color change and the enhanced luminescence efficiencies, we performed the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations of these bis-condensed DCM derivatives. The results showed that the bis-condensed DCM derivatives gave more red-shifted emission than the mono-substituted DCM derivatives. In addition, when the electron-donating ability of EDG is increased, the bandgap of the bis-condensed DCM derivative becomes small, resulting in more red-shifted emission. The PL emission maxima of bis-DCMNOEH at 600 nm showed that the excited energy was absorbed from both DCM and DCMOEH moieties. The energy placed in their excited state of the DCMOEH moiety was transferred to the DCM moiety and light was emitted from DCM moiety in the end.