Self-sorted Oligophenylvinylene and Perylene Bisimide Hydrogels

Abstract

We describe two component hydrogels with networks composed of self-sorted fibres. The component gelators are based on 1,4-distyrylbenzene (OPV3) and perylene bisimide (PBI) units. Self-sorted gels can be formed by a slow decrease in pH, which leads to sequential assembly. We demonstrate self-sorting by NMR, rheology and small angle X-ray scattering (SAXS). Photoconductive xerogels can be prepared by drying these gels. The wavelength response of the xerogel is different to that of the PBI alone.

Figure 1

Cartoon showing the sequential self- assembly of two gelators driven by differences in their pK _a values. Self-sorting of the two gelators results in a hypothetical self-sorted fibrous network. On drying, a self-sorted xerogel will be formed.

Figure 2

Structures of the two OPV3-based gelators (1 and 2) and the PBI-based gelator (3) used in this work.

Figure 3

Plots showing the evolution of the gel networks of the two component systems with time, monitored with different techniques: (a) 1 + 3, (b) 2 + 3. For (a) and (b), the top plots show the evolution of pH (red data) and rheological moduli (G′, black; G″, blue). The bottom plots show the evolution of pH (red data), integral of ¹H NMR signals due to CH groups in 1 (black in (a)), 2 (black in (b)) and 3 (blue in (a) and (b)), and SAXS (open circles). Note that the scatter of the NMR data is attributed to the inherent inaccuracy of integrating broad NMR signals (see Fig. S3 Supporting Information). The normalised value was determined from the integration of the components against the internal standard at pD 11 before the addition of GdL.

Figure 4

SAXS data and fitting. The scattering is shown for (a) a solution of 1; (b) a gel of 1; (c) a gel of 3; In all cases, the data are shown in black and the fits are shown in red. (d) shows an overlay of the scattering from a solution of 1 + 3 immediately after adding GdL (red) and after 800 minutes (black). Further SAXS data is available in the Supporting Information.

Figure 5

(a) Photocurrent at 4 V of the xerogel of 1 + 3 at different wavelengths; (b) Photocurrent at 4 V of the xerogel of 2 + 3 at different wavelengths.