Novel Quinolizine AIE System: Visualization of Molecular Motion and Elaborate Tailoring for Biological Application

Molecular motions are ubiquitous in nature and they immutably play intrinsic roles in all actions. However, exploring appropriate models to decipher molecular motions is an extremely important but very challenging task for researchers. Considering aggregation-induced emission (AIE) luminogens possess their unique merits to visualize molecular motions, it is particularly fascinating to construct new AIE systems as model to study molecular motion. Herein, a novel quinolizine (QLZ) AIE system was constructed based on the restriction intramolecular vibration mechanism. It was demonstrated that QLZ could act as an ideal model to visualize single-molecule motion and macroscopic molecular motion via fluorescence change. Additionally, further elaborate tailoring of this impressive core achieved highly efficient reactive oxygen species production and realized fluorescence imaging-guided photodynamic therapy applications, which confirms the great application potential of this new AIE-active QLZ core. Therefore, this work not only provides an ideal model to visualize molecular motion but also opens a new way for the application of AIEgens.

MANIFESTATION OF INTRAMOLECULAR VIBRATIONS IN THE FLUORESCENCE SPECTRA OF MOLECULES IN POLAR MEDIA

The effect of a low frequency intramolecular vibration on the nonstationary fluorescence spectrum of a molecule and the dynamics of the Stokes shift is analyzed in the framework of the nonstationary perturbation theory based on the operator of the interaction energy of the electric field of the exciting pump pulse with a dissolved molecule. Using a well-tested spin-boson model, which takes into account not only the reorganization of the relaxation polarization modes of the medium, but also intramolecular vibrations, an analytical expression for the time-resolved fluorescence signal is written, and the conditions under which the oscillations of the maximum of nonstationary fluorescence spectra can manifest themselves are analyzed. It is shown that the reorganization of the medium does not suppress the oscillations of the spectrum maximum.

Aggregation-Induced Emission and Large Two-Photon Absorption Cross-Sections of Diketopyrrolopyrrole (DPP) Derivatives

In this work, a new series of triphenylamine-based diketo-pyrrolo-pyrrole (DPP) compounds (DPP-I, DPP-II, DPP-III) have been designed and synthesized by a concise route. Their one- and two-photon absorption properties have been investigated. It was found that DPP-based compounds are very weakly fluorescent in THF solution, but their intensities are increased by almost 29, 9, and 24 times in water/THF (v/v 90 %) mixtures, respectively, in which they exhibit a strongly enhanced red fluorescence. The result indicates that the intramolecular vibration and rotation of these dyes is considerably restricted in nano-aggregates formed in water/THF mixtures, which leads to significant increases in fluorescence. The two-photon absorption (2PA) cross-sections measured by the open aperture Z-scan technique were determined to be 188, 275 and 447 GM for DPP-I, DPP-II, and DPP-III, respectively; DPP-III with the symmetrical structure shows the highest value of 2PA cross-section. The excellent properties of aggregation-induced emission (AIE) and 2PA provide an attractive alternative for the biophotonic materials.