Aggregation-Induced Enhanced Emission (AIEE) from N,N-Octyl-7,7′-diazaisoindigo-Based Organogel

Abstract

A new kind of low molecular-mass organic gelator (LMOG) π-electrondeficient N,N-octyl-7,7′-diazaisoindigo (1) with aggregation-induced enhanced emission (AIEE) phenomenon is described. This organogel is capable of self-assembling through intermolecular H-bonding and π−π interactions between diazaisoindigo molecules. Its rheological properties, X-ray diffraction pattern, optical properties and theoretical calculations were investigated. The AIEE effect is exhibited in fluorescence during the formation of the supramolecular organogel, which persisted in the xerogel state, and the spectral red-shifts suggest the formation of J-type aggregates during the gelation process via π−π interactions in microbelts or 3D networks. Fluorescence lifetime and quantum yield significantly increase from dilute solution to the aggregate state. From a theoretical perspective, the effect of the aggregation of 1 on the photophysical properties was also studied by means of the density functional theory (DFT). In this sense, the lowest energy electronic transitions were calculated for both the single molecule and different size aggregates in order to predict spectral shifts. In addition, the geometry and molecular properties of the excited state were analyzed in different material states.

Aggregate Science: From Structures to Properties

“…For example, in 2002, Park et al reported the compound (E)-CN-MBE with a bathochromically shifted absorption and enhanced emission within the process of aggregation due to the J-aggregate formation. [108][109][110][111] A negligible fluorescence quantum yield (Φ F ) of 0.001 was measured in a pure THF solution. However, the Φ F of nanoparticles (NPs) reached 0.69, which was attributed to the synergetic effect of intramolecular planarization and J-type aggregate formation.…”

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.…”

Shedding Light on the Origin of Solid‐State Luminescence Enhancement in Butterfly Molecules

“…Although the RIM mechanism has been successfully employed to explain the fluorescence enhancement observed in a large variety of luminogens, a thorough description of the SLE effect should involve a global study of the potential‐energy surface [12, 13] . In this sense, other mechanisms, such as RACI or the blocking of Z / E photoisomerisation, have also been associated with the fluorescence enhancement observed in the solid state or in molecular aggregates formed in solution [2, 11–13, 20, 21] . The main drawback of this global treatment is the considerable increase in computational cost associated with calculations of the electronic excited states [12, 13] .…”