A Low-Molecular-Weight Gelator Composed of Pyrene and Fluorene Moieties for Effective Charge Transfer in Supramolecular Ambidextrous Gel

Abstract

Charge-transfer (CT) gel materials obtained from low-molecular-weight (LMW) compounds through a supramolecular self-assembly approach have received fascinating attention by many researchers because of their interesting material property and potential applications. However, most of the CT gel materials constructed were of organogels while the construction of CT gels in the form of a hydrogel is a challenge because of the solubility issue in water, which considerably limits the use of CT hydrogels. Herein, for the first time, we report a new LMW gelator [N-(fluorenylmethoxycarbonyl)-N-(δ-butyric-1-pyrenyl)-l-lysine, (FmKPy)], composed of two functional moieties such as fluorenylmethoxycarbonyl and pyrene, which not only parade both hydro and organo (ambidextrous) supramolecular gel formation but also exhibit CT ambidextrous gels when mixed with an electron acceptor such as 2,4,7-trinitro-9-fluorenone (TNF). This finding is significant as the established CT organogelator in the literature did not form an organogel in the absence of an electron acceptor or lose their gelation property upon the addition of the acceptor. CT between pyrene and TNF was confirmed by the color change as well as the appearance of the CT band in the visible region of the absorption spectrum. CT between FmKPy and TNF was supported by the solvent dilution method using tetrahydrofuran as the gel breaker and pyrene fluorescence quenching in the case compound containing pyrene and TNF. The morphology of FmKPy ambidextrous gels indicates the fibrous nature while the self-assembled structure is primarily stabilized by π-π stacking among fluorenyl and pyrenyl moieties and hydrogen bonding between amide groups. The FmKPy-TNF CT ambidextrous gel retains the fibrous nature; however, the size of the fibers changed. In FmKPy-TNF CT gels, TNF is intercalated between pyrene moieties in the self-assembled structure as confirmed by fluorescence quenching and powder X-ray diffraction. The FmKPy ambidextrous gel exhibits significant properties such as low minimum gelation concentration (MGC), thixotropic nature, pH stimuli response, and high thermal stability. Upon the addition of TNF, the FmKPy-TNF CT ambidextrous gel maintains all these properties except MGC which increased for FmKPy-TNF. Because pyrene-based LMW organogels have been developed widely for many applications while their hydrogels were limited, the current finding of the pyrene-based ambidextrous fluorescent gel with the CT property provides a wide opportunity to use FmKPy as a soft material maker and also for potential applications in fields like surface coating, three-dimensional printing, and so forth.

Synthesis, photophysical, thermal properties and X-Ray studies of novel organic dyes bearing Inden-1-ylidene and fluorene

“…Numerous studies have tackled the advantages of combining pyrene or anthracene and fluorene groups into one chromophore [14,[28][29][30][31]. In this contribution, we designed two series of 1-dicyanomethylene -2-aryl-indones 2 and 3-amino-2,4-dicyano-1-aryl-9H-fluorene 3 (Chart 1) obtained by di/three-component one-pot method.…”

Pyrene-Based Co-Assembled Supramolecular Gel; Morphology Changes and Macroscale Mechanical Property

“…Among fluorescent moieties, pyrene and its derivatives have been extensively applied as probes for molecular aggregation in polymer solutions, micelles, liquid crystals, and supramolecular gels [37,38]. Pyrene, representative of π-conjugated moieties with high fluorescence and unique emission properties, have been deemed as suitable candidates for investigating molecular arrangements and co-assembled nanomaterials [39], due to their ability of excimer formation in both solution and solid state [40]. Thus, we report control of morphology and mechanical property of co-assembled supramolecular gels by varying the ratio of pyrene derivatives having a perylenediimide (1) or an alkyl chain group (2).…”

Supramolecular Hydrogel from an Oxidized Byproduct of Tyrosine

“…Ulijn and coworkers proposed a model of the hydrogelation of Fmoc-Phe-Phe-OH, which comprises both β-sheets of the peptide and π–π interactions of fluorenyl moieties . Later, Xu, Ulijn, Adams, Banerjee, Yang, Hamley, and others significantly contributed to the development of different short-peptide-based hydrogel materials. ,− They studied various stimuli-induced gelations ,,, and their potential applications in the targeted research field. ,,− …”