Junhui Jia

New dendritic gelator bearing carbazole in each branching unit: selected response to fluoride ion in gel phase

A new dendritic gelator with carbazole as the building block (HBCD) was synthesized. It was found that H-bonding between the amide groups and π-π interaction between the aromatic rings played predominant roles in the gel formation. Meanwhile, significant aggregation-induced emission enhancement was observed in the gel state due to the formation of J-aggregates and the restricted molecular motion. Notably, the gel state of HBCD can be destroyed upon addition of F(-), accompanied by fluorescence enhancement on account of the formation of N-HF(-), which could further lead to the increased coplanarity of HBCD. The sensory capability of HBCD exhibited a high selectivity towards F(-) instead of the Cl(-), Br(-), I(-) and AcO(-) anions, which could be explained by the fact that the steric hindrance of the dendrimer would go against the interactions between the larger anions and HBCD.

A Smart Gelator as a Chemosensor: Application to Integrated Logic Gates in Solution, Gel, and Film

A gelator that consisted of one benzimidazole moiety and four amide units was used as a chemosensor. We found that its absorption and emission spectra in solution were sensitive to two complementary chemical stimuli: protons and anions. Thus, YES and INH logic gates were obtained when absorbance was defined as an output. A combination gate of XNOR and AND with an emission output was also obtained. Moreover, wet gels in two solvents were used to construct two more-complicated three-input-three-output gates, owing to the existence of the gel phase as an additional output. Finally, in xerogel films that were formed from two kinds of wet gels, reversible changes in their emission spectra were observed when they were sequentially exposed to volatile acid and NH(3). Another combination two-output logic gate was obtained for xerogel films. Finally, three states of the gelator were used to construct not only basic logic gate, but also some combination gates because of their response to multiple chemical stimuli and their multiple output signals, in which one chemical input could erase the effect of another chemical input.

Amplifying emission enhancement and proton response in a two-component gel

A glutamide gelator, 1, was synthesized, and a weak emission enhancement was observed during its gelation. In addition, 1 could be an excellent scaffold for successfully embedding an energy acceptor, 2, into its aggregate to obtain highly efficient energy transfer. An amplification of the emission enhancement was observed in the two-component gels compared to that of the neat gel of 1 during gel formation. For example, 1 induced only a 2.5-fold increase in emission intensity, whereas a 23-fold enhanced emission could be observed in the two-component gel with only 1.6 mol % 2. Furthermore, two-component gels had an excited proton response. In systems with low acceptor concentrations, the hot solution red-shifted the fluorescence from blue to yellow upon the addition of a proton, which continuously blue-shifted with decreasing temperature to form the gel given that the binding of the gelator to the proton is weakened during coassembly. Moreover, the casting film formed by the two-component wet gel had an excellent response to volatile acids such as hydrochloric acid, trifluoroacetic acid, and so on and could be reversibly recovered by exposure to NH(3).

Two-component gel of a D–π–A–π–D carbazole donor and a fullerene acceptor

A D–π–A–π–D carbazole derivative (PCQ) with a quinoxaline moiety was designed and synthesized. Its photophysical properties in solution were studied. Moreover, PCQ was found to be a highly efficient gelator toward various apolar and polar organic solvents with the critical gelation concentrations (CGCs) as low as 0.06 wt/vol%. Spectral studies and molecular dynamic stimulation revealed that the intermolecular H-bonds and π–π stacking interactions might be responsible for guiding the self-assembly processes and the gel formation. Interestingly, PCQ could construct two-component gel with fullerene derivative driven by intermolecular hydrogen bonds. Moreover, the two-component gel film could generate photocurrent under light irradiation, indicating photo-induced electron transfer from the PCQ aggregate to the fullerene derivative.

Synthesis, Mechanochromism and Acid Response of the Fluorescence Dyes Based on Quinoxalines Modified with Tetraphenylethylenes

Three new D-π-A type quinoxalines modified with tetraphenylethylenes BTPQ, DBTPQ and BTBQ were synthesized via Suzuki coupling reactions between (4-(1,2,2-triphenylvinyl)phenyl)boronic acid and bromo aromatic hydrocarbons. It was found that BTPQ and DBTPQ, in which tetraphenylethylenes were substituted on 5,8-positions of quinoxalines gave the absortion bands at 316 nm and 303 nm, respectively, originated from π-π* transition. For BTBQ, in which tetraphenylethylene units were located at 2,3-positions of quinoxaline, the π-π* transition absorption blue-shifted to 287 nm on account of the poor planarity and low conjugation. Meanwhile, the intermolecular charge transfer (ICT) emission could be detected for BTPQ and DBTPQ, whose emission bands red-shifted significantly and emission intensities decreased with increasing the solvent polarities. It should be noted that the three compounds exhibited aggregation-induced emission (AIE) behaviors. For instance, when the water faction in the THF solution increased to 90%, the emission intensity at ca. 400 nm for BTBQ, was ca. 54 times higher than that in THF. Additionally, trifluoroacetic acid (TFA) could lead to the changes of color and emitting color of BTBQ in solution as well as in solid state due to the formation of protonated quinoxaline. We found that the grey solid of BTBQ could turn into red one upon exposed to gaseous TFA, accompanying with the quench of the emission. Other kinds of acids of HCl, HNO3 and acetic acid also could lead to the fluorescence quenching of solid BTBQ to some extent. Therefore, BTBQ could be used as sensory material to detect acid vapors by naked eyes. However, the protonation would be prohibited in BTPQ and DBTPQ on account of the steric effect of tetraphenylethylene units linked to 5,8-positions of quinoxaline, so BTPQ and DBTPQ could not detect acid. Interestingly, the solid emitting colors of BTPQ as well as DBTPQ were quite different before and after grinding, exhibiting mechanochromic properties. The as-prepared crystal of BTPQ emitting blue light under UV irradiation could be changed into amorphous powder with bluish green emission. The XRD patterns suggested that the mechanochromism was originated from the transition between the crystalline and amorphous states. Such mechanochromism was reversible under the treatment of grinding and heating/fuming with DCM.