•The luminescence of anthrancene-based acylhydrazone derivative AHP-mB8 can be tuned by heating and grinding.•The AHP–mB8 xerogel from cyclohexane shown obviously mechanofluorochromism.•The mechanofluorochromism and thermochromism of AHP–mB8 is attributed to the result of soild–solid phase transition.This report describes that the luminescence of anthracene-based acylhydrazone derivative AHP−mB8 can be tuned by physical stimuli, such as heating and grinding. The AHP−mB8 xerogel from cyclohexane shows obviously mechanofluorochromic behaviour with the emission colors changing from blue to green upon grinding, whereas the ethanol xerogel shows yellowish-green light emission, which is almost unchanged after grinding. In the other hand, the ethanol xerogel exhibits thermofluorochromic with the emission colors changing from yellowish-green to blue upon heating. Based on SEM, XRD, DSC and Uv-vis studies, the observed mechanofluorochromism and thermochromism of AHP−mB8 is attributed to the result of solid–solid phase transition.The luminescence of anthracene-based acylhydrazone derivative AHP−mB8 can be tuned by heating and grinding.Download high-res image (199KB)Download full-size image

•The hydrazide derivatives allow highly selective response to anion.•The hydrazide derivatives with one hydrazide groups can only response to F−.•With two hydrazide groups can respond to F− and AcO−.•These responses are accompanied by changes in the status and color.•We can adjust the response to anion by changing the number of hydrazide groups.Two symmetric hydrazide derivatives with different numbers of hydrazide groups were synthesized, and their anion responsive behaviors were studied. The UV–vis spectra showed that the compounds with only one hydrazide group can allow highly selective fluoride detection, whereas the compound with two hydrazide groups can respond to F− and AcO−. This is due to the difference in the acidity of the compounds, which is caused by the quantity of hydrazide. This demonstrates that altering the number of hydrazide groups can realize the effective adjustment and control of the anionic recognition ability of compounds.

An anthracene-based gelator (AHP-mB8) has been designed and synthesized. AHP-mB8 can form thermo-reversible gels in some of the tested solvents. FTIR, temperature-dependent 1H NMR, UV–vis and XRD spectra indicated that the gelator self-assembles into a fibrous network possibly due to the combination of intermolecular hydrogen bonding and π–π interactions. The anion binding studies indicated that AHP-mB8 has remarkable and specific F− selectivity over other tested anions to exhibit yellow-red color changes for easy naked-eye detection. The Enhanced Fluorescence Emission has been observed after gelation although the dilute solution of AHP-mB8 was almost non-fluorescent.The organogel of an anthracene derivative exhibited gelation-induced enhanced fluorescence emission, and it was selectively fluoride-responsive among test anions, expressing gel–sol transition and yellow-red color changes for easily naked-eye detection.

•The dimeric hydrazide derivative with methyl groups and phenyl groups can allow highly selective fluoride detection•The nature of terminal substituents affect acidity of compounds, as a consequence they show different anion sensing property•The number of hydrazide groups and the nature of the terminal substitute don’t affect the fluoride anion responsive mechanism•By altering terminal substituent groups, the anionic recognition ability of compounds could be adjusted and controlledThree dimeric hydrazide derivatives with nitro, phenyl, and methyl terminal substituents were synthesized and their anion responsive behaviors were studied. The UV–vis spectra showed that the compounds with methyl groups and phenyl groups can allow highly selective fluoride detection, whereas the compound with terminal nitro substituent can respond to F−, AcO− and H2PO4−, due to the distinction on acidity of compounds which is caused by electronic effect and field effect of terminal substituents. The 1H NMR spectra revealed that the anion responsive mechanism for F−, AcO− and H2PO4− was different due to the much lower basicity of AcO− and H2PO4− compared to F−. Whereas the number of hydrazide groups and the nature of the terminal substitute do not affect the fluoride anion responsive mechanism. It demonstrates that, by altering terminal substituent groups, the anionic recognition ability of compounds could be adjusted and controlled.The hunt for fluoride: Three dimeric hydrazide derivatives with nitro, phenyl, and methyl terminal substituents, all have colorless solution. When different anions were added, the sensing processes change the color of solution. Different terminal substituents bring various colors, and through conjugative effects they alter the acidity of compounds, as a consequence, change the affinity to different anions, so highly selective fluoride detection achieved.

A 4-nitrobenzohydrazide derivative, N-(3,4,5-octyloxybenzoyl)-N′-(4′-nitrobenzoyl)hydrazine (C8), was synthesized. It could form stable gels in some of the tested organic solvents. The wide-angle X-ray diffraction analysis showed that the xerogels exhibited a layered structure. SEM images revealed that the molecules self-assembled into fibrous aggregates in the xerogels. FT-IR studies confirmed that the intermolecular hydrogen bonding between CO and N–H groups was the major driving force for the formation of self-assembling gel processes. The gel is utilized for a ‘naked eye’ detection of fluoride ions, through a reversible gel–sol transition, which is associated with a color change from colorless to red. An extended conjugated system formed through the phenyl group and a five-membered ring based on intramolecular hydrogen bonding between the oxygen atom near the deprotonation nitrogen atom and the other NH, which is responsible for the dramatic color change upon addition of fluoride ions.

The vibrational bands of a dihydrazide derivative, 1,4-bis[(3,4,5-trihexyloxyphenyl)hydrazide]phenylene (TC6), observed in the Raman and infrared spectra were assigned. The intermolecular hydrogen bonding vibrational bands due to CO and NH groups in the low-frequency Raman spectra were observed at 111 and 94 cm−1 in the crystalline and liquid crystalline (LC) phases, respectively. The sequential order of changes in the hydrogen bonding and alkyl chains was opposite in the crystalline and LC phases. The modifications in the hydrogen bonding occurred prior to conformational changes in the hydrocarbon chains in the crystalline phase; however, a reverse trend was observed in the LC phase. Simultaneously, the two-dimensional (2D) IR and Raman correlation spectroscopic analysis showed that the amide I band of TC6 in the LC phase comprised at least five distinct bands. In addition, the hetero 2D correlation between the NH and CO groups confirmed that no free NH and CO groups existed in the LC phase.

A new series of liquid-crystalline tapered hydrazide derivatives with an amino head group, e.g. N-(3,4,5-trialkoxylbenzoyl)-N′-(4′-aminobenzoyl) hydrazine (Dn, where n is the number of carbon atoms in the alkyl chains, n = 6, 8, 16), were designed and synthesized. Results of 1H NMR diluting experiment and FTIR spectroscopy revealed that the amide protons of the central hydrazide group in Dn participated in intermolecular double hydrogen bonds based on CO and NH in liquid crystalline phase. Investigations on the liquid crystalline properties showed that the D6 exhibited non-mesophase, D8 exhibited monotropic hexagonal columnar mesophase, while D16 exhibited enantiotropic oblique columnar mesophase with increasing the length of the terminal chains.Highlights► We aimed at developing new liquid-crystalline hydrazide derivatives. ► The columnar mesophases are observed in these hydrazide derivatives. ► Experimental results revealed that the amide protons of the central hydrazide group participated in intermolecular double hydrogen bonds based on CO and NH in mesophase. ► The intermolecular hydrogen-bonding interaction among dihydrazine units is the main driving force to form the mesophase.

A 4-nitrobenzohydrazide derivative, N-(3,4,5-octyloxybenzoyl)-N′-(4′-nitrobenzoyl)hydrazine (C8), was synthesized. It could form stable gels in some of the tested organic solvents. The wide-angle X-ray diffraction analysis showed that the xerogels exhibited a layered structure. SEM images revealed that the molecules self-assembled into fibrous aggregates in the xerogels. FT-IR studies confirmed that the intermolecular hydrogen bonding between CO and N–H groups was the major driving force for the formation of self-assembling gel processes. The gel is utilized for a ‘naked eye’ detection of fluoride ions, through a reversible gel–sol transition, which is associated with a color change from colorless to red. An extended conjugated system formed through the phenyl group and a five-membered ring based on intramolecular hydrogen bonding between the oxygen atom near the deprotonation nitrogen atom and the other NH, which is responsible for the dramatic color change upon addition of fluoride ions.