Unraveling the aggregation effect on amorphous phase AIE luminogens: a computational study

Abstract

To achieve the efficient and precise regulation of aggregation-induced emission (AIE), unraveling the aggregation effects on amorphous AIE luminogens is of vital importance. Using a theoretical protocol combining molecular dynamics simulations and quantum mechanics/molecular mechanics calculations, we explored the relationship between molecular packing, optical spectra and fluorescence quantum efficiency of amorphous AIE luminogens hexaphenylsilole (HPS). We confirmed that the redshifted emission of amorphous aggregates as compared to crystalline HPS is caused by the lower packing density of amorphous HPS aggregates and the reduced restrictions on their intramolecular low-frequency vibrational motions. Strikingly, our calculations revealed the size independent fluorescence quantum efficiency of nanosized HPS aggregates and predicted the linear relationship between the fluorescence intensity and aggregate size. This is because the nanosized aggregates are dominated by embedded HPS molecules which exhibit similar fluorescence quantum efficiency at different aggregate sizes. In addition, our results provided a direct explanation for the crystallization-enhanced emission phenomenon of propeller-shaped AIE luminogens in experiments. Our theoretical protocol is general and applicable to other AIE luminogens, thus laying solid foundation for the rational design of advanced AIE materials.

Real-time monitoring of hydrophobic aggregation reveals a critical role of cooperativity in hydrophobic effect

“…2b,c, symbol points) were linearly correlated with the total amount of aggregated HPS. This linear correlation was validated by quantum mechanics/molecular mechanics calculations39, fluorescence AFM experiments and spectrophotometer experiments (Supplementary Figs 1–4, 13, 19 and 20; Supplementary Notes 2 and 6). …”

Exploring Potential Energy Surfaces for Aggregation‐Induced Emission—From Solution to Crystal

“…In AIEgens dominated by the RIM mechanism, the reorganization energies of the modes with larger contributions to the internal conversion rate, k IC , are hampered in the aggregated state owing to the steric restrictions. In this context, the evaluation of the Huang–Rhys factors, S j , and the reorganization energies, λ i , have become very popular for the semi‐quantitative interpretation of AIE …”

“…In this context, the evaluation of the Huang-Rhys factors, S j ,a nd the reorganization energies, l i ,h ave become very popular for the semi-quantitative interpretation of AIE. [10,12,[21][22][23][25][26][27][28][29][30][31][32] The mosts ophisticated approaches include the consideration of the mixing between the excited and ground state vibrations by using Duschinsky rotationm atrices and the path integral framework. [11,23,33] These approaches have been implemented in ac ode called MOMAP.…”

“…The initial research on AIEgens focusedo ns iloles and propeller-shapedc ompounds where the effect of exciton formation is minimal. [8,16,22,25,26,28,77] Consequently,i th as been assumed that in the mechanism of AIE,t he environment acts as ap erturbation to the excited states of ac entral molecule. Most simulations of AIEgens follow this idea and use QM/MM methods where only one molecule is included in the QM region.…”

“…[26,91] In ar ecent investigation using the FGR-RIM model, embedded and exposed molecules in amorphous nanoparticles of HPS with different sizes were considered ( Figure 17). [26] The average reorganization energies (l)o fe mbedded molecules are size independent and similar to those of the crystal,w hereas for the exposed molecules, the values are closer to those obtained fort he isolated molecule in the gasp hase. The quantum efficiencies of embedded molecules do not depend on the size of the particles and have F f > 92.7 %, similart ot he value for the crystal (F f = 97.9 %).…”