Abstract
Aggregation-induced emission (AIE) spectra accompanied by excited state intramolecular proton transfer (ESIPT) for two triphenylamine salicylaldehyde derivatives (namely, TS and TS-OMe) are investigated by performing molecular spectral and dynamics simulations associated with the hybrid quantum mechanics/molecular mechanics (QM/MM) at the quantum level of the time-dependent density functional theory. The simulated emission spectral peaks and Stokes' shifts are in good agreement with the experimental results for both TS and TS-OMe. Furthermore, the AIE spectral mechanisms are well explained to be associated with the ESIPT processes for both TS and TS-OMe monomers in the aggregated crystal state, while the AIE spectra mechanism for the TS-OMe (TS) dimer is accompanied by intermolecular charge-transfer excitation process. Besides, the TS dimers also contributed to the AIE mechanisms in the crystal with the intermolecular charge-transfer from one monomer to another. In addition, the TS dimers are contributed to the AIE mechanisms in the crystal with the intermolecular charge-transfer from one monomer to another. On the other hand, simulated emission spectra for both the TS and TS-OMe monomers in acetonitrile solution are involved in mixed emission with and without the ESIPT process, as interpreted by nonadiabatic molecular dynamics simulation. It is also briefly addressed that the emission spectra in the solution are weak and enhanced in the crystal. The present study provides a great physical insight into the design of highly efficient AIE compounds.
Highlights
Organic luminescent materials have attracted great attention for several decades because of their varied applications in organic light-emitting diodes (OLEDs), bioimaging, and chemical sensing.[1,2,3] Generally speaking, organic luminescent materials exhibit a remarkably high luminescence efficiency in dilute solvents but their efficiency is signi cantly reduced in the solid state, mainly due to the formation of aggregation-caused quenching (ACQ)
Aggregation-induced emission (AIE) spectra accompanied by excited state intramolecular proton transfer (ESIPT) for two triphenylamine salicylaldehyde derivatives are investigated by performing molecular spectral and dynamics simulations associated with the hybrid quantum mechanics/molecular mechanics (QM/MM) at the quantum level of the time-dependent density functional theory
The key geometry parameters related to hydrogen bonds H1–O1 and H1–O2, and dihedral angle q, and the relative energies are summarized in Table S5 (ESI†)
Summary
Organic luminescent materials based on the coupling of AIE and ESIPT mechanisms have drawn widespread attention in bioimaging due to their high efficiency emission in the solid state and large Stokes' shi s.22,23 Generally speaking, ESIPT is a four-level photochemical process that takes place in the strong intramolecular hydrogen bonds transfer. In 2020, Zhao and coworkers[32] designed and synthesized three triphenylamine salicylaldehyde (TS) derivatives, namely, TS, TS-OMe (methoxy-substituted TS), and TSNMe2 (dimethylamine-substituted TS), and all three showed AIE and ESIPT characteristics in the aggregated solid state. Their experiment showed that the TS derivatives in the aggregated solid state exhibited intense uorescence emission and Stokes' shi s larger than 140 nm wavelength. They speculated that this must be due to the ESIPT mechanism. We investigate the AIE spectra for the TS and TS-OMe dimers in comparison with their AIE spectra in order to deeply understand their emission nature in the solid state
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