Modulation of Symmetry-Breaking Intramolecular Charge-Transfer Dynamics Assisted by Pendant Side Chains in π-Linkers in Quadrupolar Diketopyrrolopyrrole Derivatives

The effect of the length of pendant side chains in centrosymmetric quadrupolar molecules on dynamics of their most perplexing photophysical phenomenon, i.e., symmetry-breaking intramolecular charge transfer, has been discovered. Unexpectedly, considerable influence of length of these pendant side chains in pi-linkers arose as a structural factor enabling the control of the degree of fluorescence solvatochromism. The symmetry-breaking intramolecular charge transfer dynamics has been described on quadrupolar diketopyrrolopyrrole derivatives possessing fluorene moieties as pi-linkers and diarylamino groups as electron donors. On the basis of the evolution of transient fluorescence spectra obtained by a femtosecond broadband fluorescence up-conversion spectroscopy, it was found that the relative contribution of diffusive solvation and torsional relaxation in overall spectral relaxation can be modulated by the length of pendant side chain in pi-linkers. Consequently, we demonstrated that this modulation plays a significant role in determining the photophysical properties of diketopyrrolopyrroles in a polar medium.