Intramolecular charge transfer in the dye molecules containing bis-dimethylfluoreneaniline

Two novel metal-free organic dyes (JK-1, JK-2), composed of bis-dimethylfluoreneaniline moiety as the electron donor and cyanoacrylic acid moiety as the electron acceptor, are theoretically investigated with quantum chemical methods. The energies and densities of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), as well as the binding energies, are compared between the two dyes. The HOMO → LUMO electronic transition describes their lowest singlet excited states. The orientation and strength of transition dipole moment are revealed visually with transition density. We also show the orientation and results of the intramolecular charge transfer with charge difference density. Transition density matrices provide information about the electron-hole coherence and excitation delocalization. Theoretical results reveal that exciton size and transition dipole moment increase with the expansion of the π conjugation and the charge transfer occurs from donor unit across the π bridge to the acceptor unit.