Versatile robust organogels based on a low molecular weight gelator of phenylquinolinylacrylonitrile

Abstract

Herein, we have synthesized three new phenylquinolinylacrylonitrile derivatives. It is found that ((Z)-2-phenyl-3-(quinolin-4-yl)acrylonitrile) (1) and ((Z)-2-(4-fluorophenyl)-3-(quinolin-4-yl)acrylonitrile) (2) can form organogels in polar solvents, and compound 2 shows good gelation ability in acetone/H₂O (v/v = 1/1.3) with a low critical gelation concentration (CGC) of 0.11 wt%. Interestingly, the free standing organogel (FSOG) with remarkable mechanical strength can be formed from gelator 2 based on its strong self-assembling capability. The storage modulus of FSOG was measured to be up to the 10⁴ Pa level at a low concentration (0.74 wt%), which is much higher than those of most LMWGs. The FSOG exhibited reversible external force-induced bending without breaking and we could cut it arbitrarily. Immersing the FSOG in water for several hours affords the free-standing hydrogel (FSHG). Since a dense film was formed on the surface of FSHG, the mechanical strength of FSHG was further improved compared with that of FSOG. When exposed to 365 nm light, the freshly prepared organogel would be collapsed into a suspension because 2 underwent the tandem reactions of isomerization, electrocyclization and oxidative aromatization to yield 3-fluorobenzo[i]phenanthridine-12-carbonitrile (4) to destroy the intermolecular interactions among the molecules of 2. In addition, due to the aggregation-induced emission of compounds 1 and 2, the gained xerogels exhibited bright fluorescence. For instance, the blue fluorescence of the xerogel film of 2 could be switched off by TFA (trifluoroacetic acid) vapor with a response time of 0.38 s and a detection limit of 0.43 ppm.