Efficient crystallization induced emissive materials based on a simple push–pull molecular structure

Abstract

Solid state luminescent materials are the subject of ever growing interest both from a scientific and a technological point of view. Aggregation caused quenching (ACQ) processes however represent an obstacle to the development of most luminogens in the condensed phase. This is why particularly fascinating are those materials showing higher emission intensity in the solid state than in solution. Here we report on three 4-dialkylamino-2-benzylidene malonic acid dialkyl esters, very simple push-pull molecules, which are hardly emissive in solution and in the amorphous phase but become good emitters in the crystalline phase according to what has been indicated as crystallization induced emission (CIE). Thanks to combined emission and NMR spectroscopies at different temperatures on the prototype compound 4-dimethylamino-2-benzylidene malonic acid dimethyl ester in solution, we give full evidence that a restricted intramolecular rotation (RIR) phenomenon, in particular the hindered rotation around the aryl main axis of the compound, is at the origin of this behaviour. In addition, solid state photophysical and X-ray diffraction structural characterization allow us to identify J-dimeric interactions as responsible for the particularly intense emission of two of the three compounds. Moreover, by exploiting the compounds' acidochromic properties, applications in sensors and optoelectronics are envisaged.

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

“…Another AIEgen with as imilar mechanism is 4-diethylamino-2-benzylidene malonic acid dimethyl ester (BIM), which contains as tyrene unit ( Figure 2). [59] Calculations combining TD-DFT,C ASSCF,a nd CASPT2 show that the molecule in methanol solutionr elaxes, initially,t oa ne xcited-state minimum with FClike structure, S 1 -EM. [44] However,a long the torsion coordinate of the styrene double bond there is af urther S 1 minimum, S 1 -CT,a nd aC I, S 1 /S 0 -CIb, at 908 and1 208 twist, respectively, where the excited state is aC Tstate from the benzene to the diesterm oiety ( Figure 4).…”

Long-living optical gain induced by solvent viscosity in a push–pull molecule

“…33 Assuming a = 5.36 Å, as estimated by computing the volume inside an isosurface of 0.001 e bohr À3 density, a fit from eqn (1) gives a value of m E À m G = 6.9 D (see Fig. 29,30 In the following we will focus our attention on the photophysical study of 1 dissolved in two solvents possessing different viscosities, acetonitrile (ACN, non-viscous) and polyethylene glycol (PEG, viscous), whose optical properties are reported in Fig. When the molecule is dissolved in viscous solvents, this simple relation does not hold, suggesting that additional effects, specifically related to solvent viscosity, have to be considered in the photoexcitation pathway.…”

“…11,29,30 In this paper, in order to shed more light on the excited state properties of push-pull systems and on the TICT mechanism, we report on the optical behavior of a new molecule, 1,1,1,5,5,5-hexafluoro-3-( p-dimethylaminophenyl)methylene-2,4-pentanedione, 1 (see Fig. 11,29,30 In this paper, in order to shed more light on the excited state properties of push-pull systems and on the TICT mechanism, we report on the optical behavior of a new molecule, 1,1,1,5,5,5-hexafluoro-3-( p-dimethylaminophenyl)methylene-2,4-pentanedione, 1 (see Fig.…”

Aggregation-Induced Nonlinear Optical Effects of AIEgen Nanocrystals for Ultra-Deep in Vivo Bio-Imaging

“…Such observations were consistent with the characteristics of CIE behavior and were commonly observed in AIE luminogens with blue to yellow emission. [47][48][49][50][51][52][53][54]56 For better understanding this phenomenon, the morphology evolution of aggregates formed in 50% aqueous solution was studied at different time intervals during storage. The scanning electron microscopic (SEM) image of nanoaggregates of the asprepared suspension revealed spherical morphology as a result of quick precipitation ( Fig.…”

“…It is an effective way to increase the brightness of many AIEgens. [47][48][49][50][51][52][53][54][55] However, the preparation of crystals with sizes suitable for biological imaging is tricky. Liu et al reported a stress-induced seed assisted crystallization method, which can produce uniform AIE nanocrystals with sizes of around 100 nm.…”