Globular Aggregates Stemming from the Self-Assembly of an Amphiphilic N-Annulated Perylene Bisimide in Aqueous Media

Abstract

Herein, we describe the synthesis of highly emissive amphiphilic N-annulated PBI 1 decorated with oligo ethylene glycol (OEG) side chains. These polar side chains allow the straightforward solubility of 1 in solvents of different polarity such as water, iPrOH, dioxane, or chloroform. Compound 1 self-assembles in aqueous media by π-stacking of the aromatic units and van der Waals interactions, favored by the hydrophobic effect. The hypo- and hypsochromic effect observed in the UV-Vis spectra of 1 in water in comparison to chloroform is diagnostic of H-type aggregation. Solvent denaturation experiments allow deriving the free Gibbs energy for the self-assembly process in aqueous media and the factor m that is indicative of the influence exerted by a good solvent in the stability of the final aggregates. The ability of compound 1 to self-assemble in water yields globular aggregates that have been visualized by TEM imaging.

Thermodynamics of the self-assembly of N-annulated perylene bisimides in water. Disentangling the enthalpic and entropic contributions

“…The formation of H-type aggregates from amphiphiles 2–4 in aqueous media is demonstrated by the hypso- and hypochromic effect observed in the UV-vis spectra of the aggregated species compared to the monomeric species. 19 In the case of the T-shaped compounds 3 and 4 , endowed with the lateral terphenyl moiety, the intense band at ∼300 nm displayed in dioxane also experiences a slight hypsochromic and a strong hypochromic effect upon addition of water, which is diagnostic of the participation of this segment in the π-stacking of the aromatic backbone, which yields the final H-type aggregates. The formation of H-type aggregates is corroborated by the strong quenching of the emissive features of the monomeric units upon aggregation (Fig.…”

“…21 On the other hand, the dianhydride 12 bearing the hydrophilic terphenyl segment was prepared by a copper-assisted nucleophilic substitution of 4,4′-diiodo-1,1′-biphenyl and subsequent Suzuki cross-coupling reaction with the boronic acid 10 . 21 a The final nucleophilic addition of amine 8 21 b or 13 19 in the presence of Zn(AcO) 2 and imidazole yields the amphiphilic N -PBIs 2–4 .…”

“…The synthesis of N -PBIs 2–4 was accomplished following a similar protocol to that reported previously for compound 1 . 19 It involves a convergent methodology in which the preparation of the hydrophilic peripheral wedges and the synthesis of the N -annulated tetraester perylene 5 are key steps (Scheme S1‡). The dendritic amino-based wedge 13 and the tetraester 5 were prepared following previously reported methodologies.…”

“…The dendritic amino-based wedge 13 and the tetraester 5 were prepared following previously reported methodologies. 19,20 The synthesis of the hydrophilic amine 8 begins with the O -alkylation of the hydroxy groups of commercial pyrogallol. The selective mononitration and the subsequent catalytic hydrogenation of the nitro group afford aniline derivative 8 in good yield.…”

“…2a). 19,22,23 In aqueous media, a clear hypsoand hypochromic effect is observed, with absorption maxima at 543 and 503 nm and a shoulder at 478 nm, which implies the formation of H-type aggregates. Similar changes have been observed for amphiphiles 2-4 (Fig.…”