Engineering Isomeric AIEgens Containing Tetraphenylpyrazine for Dual Memory Storage

Abstract

Tetraphenylpyrazine (TPP) is a promising heterocycle-based aggregation-induced emission luminogen (AIEgen) which has sparked multiple applications in organic light-emitting diodes, sensors, and biotherapy. However, the utility of it in developing information storage materials is relatively rare. Moreover, TPP is mostly employed as an electronic acceptor in molecular design, while the consideration of it as an electronic donor is attractive in studies which may provide a full understanding of its property to tailor the materials. In this work, we synthesize three TPP-based molecules by decorating it with acrylonitrile and isomeric pyridine units, which show AIE behavior by property inheritance from their parent unit. Interestingly, the effective intramolecular charge transfer takes place from the TPP electronic donor to the acrylonitrile and pyridine electronic acceptor, therefore inducing a remarkable solvatochromic effect as the solvent polarity improves. Moreover, it is revealed that the isomeric effect of the nitrogen atom in the pyridines may pose an influence on the absorption, solvatochromism, and AIE behavior. In addition, the acrylonitrile and pyridine groups are reactive to light and acid-base stimuli with irreversible and reversible responses, respectively. Combined with the high light-harvesting ability of these AIEgens, they show great potential in the stimuli-responsive materials for dual information storage.

Scheme 1. Synthetic Route to TPP-Based AIE Isomers and the Roles of Each Unit in the Molecules

Figure 1

UV–vis spectra of AIE isomers in THF, [dye] = 10 μM.

Figure 2

PL spectra of (A) TPP-p-Py, (B) TPP-m-Py, and (C) TPP-o-Py in THF/water mixture with different f_w, [dye] = 10 μM, λ_ex = 370 nm; (D) Changes of relative PL intensities (I/I₀) versus f_w in these AIEgens.

Figure 3

(A) UV–vis and (B) PL spectra of TPP-p-Py in different solvents, [dye] = 10 μM, λ_ex = 370 nm. (C) Plot of Stokes shift (Δυ) of AIE isomers versus Δf of solvents. (D) Photographs of AIE isomers in different solvents taken under 365 nm UV light.

Figure 4

Molecular orbitals, energy levels, and energy gaps based on S₀ conformation of AIE isomers optimized at B3LYP/6-31G (d, p) level.

Figure 5

PL spectra of (A) TPP-p-Py, (B) TPP-m-Py, and (C) TPP-o-Py in THF/water mixtures with f_w = 90% under continuous UV light irradiation, [dye] = 10 μM, λ_ex = 370 nm. (D) Changes relative PL intensities (I/I₀) versus time in AIEgens.

Figure 6

PL spectra of powders of (A) TPP-p-Py, (B) TPP-m-Py, and (C) TPP-o-Py with different treatments, λ_ex = 370 nm. (D) Changes of emission wavelengths of AIE isomers during 5 cycles of acid–base responses.

Figure 7

Dual information storage with AIE isomers under acid–base and UV light responses.