Engineering Stacks of V‐Shaped Polyaromatic Compounds with Alkyl Chains for Enhanced Emission in the Solid State

Abstract

AV-shaped bisanthracene derivative with three butyl groups formed two types of emissive solids that displaybluish green and blue fluorescence (F F = 72 and 32 %, respectively), depending on the preparation conditions.T he crystal and powder X-raya nalyses reveal that the highly emissive solid adopts ah ead-to-head arrangement with discrete stacks of the anthracene moieties,w hereas the moderately emissive solid adopts ah ead-to-tail arrangement without the stacks.T he obtained molecular arrangements are transformed by thermal stimuli accompanying the change in fluorescence.F urthermore,l arge enhancements of dye emissions (12-45-fold) through highly efficient host-guest energy transfer were achieved in the solid state by adding minute amounts of various fluorescent dyes (e.g. rubrene and Nile red) to the Vshaped compound.Polyaromatic compounds with peripheral substituents often form well-ordered columnar stacks in the solid state (Figure 1a).[1] However,t he emissive ability of the polyaromatic moieties found in dilute solutions is apt to be lost or weakened in such infinite structures owing to nonradiative decay of the excited states through extensive aromatic-aromatic interactions.F ull encirclement of polyaromatic compounds by molecular capsules [2,3] or bulky substituents [4][5][6] can prevent infinite stacking of the fluorophores (Figure 1b)sothat most of them show simple emissions from the monomeric species. In contrast, dimeric stacks of polyaromatic molecules have received considerable attention, because their structures sometimes exhibit intriguing fluorescence behavior derived from the formation of excimers. [7] However,t here is no general and rational approach to prepare highly fluorescent dimeric stacks of polyaromatic compounds through noncovalent interactions.[8] To exploit anew class of polyaromatic solids with agreater emissive ability,wedesigned aV -shaped polyaromatic compound bearing bulky substituents on the convex side to engineer 1) the dimeric stack of the bent polyaromatic frameworks (Figure 1c)a nd 2) the layered arrays of the polyaromatic dimers through intermolecular interactions between the substituents.H ere we report the unusual emission behavior of V-shaped bisanthracene derivative 1 with three butyl groups (Figure 1d)i nt he solid state.TheV -shaped compound forms two different types of solids depending on the preparation conditions.T he solid with ah ead-to-head arrangement (Figure 1c)s hows strong bluish green fluorescence (F F = 72 %) as ac onsequence of finite stacks of the anthracene moieties.Incontrast, the other solid with ah ead-to-tail arrangement shows moderate blue fluorescence (F F = 32 %). Them olecular arrangement and emissive states can be changed by thermal stimuli. In addition, the solid-state emission properties of various fluorescent dyes (e.g. rubrene and Nile red) are greatly enhanced (12-45-fold) by mixing them with the bisanthracene derivative upon single irradiation with UV light (e.g. l = 368 nm), because of highly efficient energy transfer from ...

Highly Efficient Orange-Red/Red Excimer Fluorescence from Dimeric π–π Stacking of Perylene and Its Nanoparticle Applications

“…Though the PL efficiency of mTPA-3PE crystal is not as high as those of AN excimer we have reported previously, it is much better than some classic red dyes, such as 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran, rubrene and Nile red, and so forth. 32 Besides, for the future practical application, the neat thin film of mTPA-3PE was also prepared by vacuum evaporation, and its emission is peaked at about 600 nm (Figure S4a). Although the emission of neat film is some blue-shifted relative to that of crystal, the transient PL spectrum confirms that there is long lifetime component (Figure S4b), indicating the formation of PE excimer to a certain degree.…”

Unraveling Molecular Assembly and Tracking Lipid Droplets Dynamics using Fluorescent Phenanthroimidazole Derivatives

“…In this context, the integration of long alkyl chains into the rigid and π-conjugated molecular backbone prevents the π-π stacking in the aggregated state, resulting in enhanced fluorescence. [43][44][45][46] Additionally, the tuning of intermolecular interactions through the variation of alkyl chains may govern the nature of self-assembly, leading to various structures like particles, tubes, fibers, etc. [47][48][49][50] Moreover, the hydrophobicity of the alkyl chains improves the propensity of the probe to target the hydrophobic dynamic organelle like lipid droplets (LDs).…”