Mechanofluorochromic Properties Research Articles

The effect of N-alkyl chain length on the photophysical properties of indene-1,3-dionemethylene-1,4-dihydropyridine derivatives

AIEE-active indene-1,3-dionemethylene-1,4-dihydropyridine derivatives exhibit reversible alkyl-length-dependent mechanofluorochromic properties.

Effects of cyano groups on the properties of thiazole-based β-ketoiminate boron complexes: aggregation-induced emission and mechanofluorochromism

The triphenylamine-functionalized thiazole-based β-ketoiminate boron complexBF2-TT-CNexhibited strong cyano-dependent aggregation-induced emission (AIE) and mechanofluorochromic (MFC) properties.

Aggregation-induced emission enhancement and mechanofluorochromic properties of α-cyanostilbene functionalized tetraphenyl imidazole derivatives

Twisted tetraphenyl imidazole derivatives functionalized by α-cyanostilbene possess aggregation-induced emission enhancement and mechanochromic luminescence properties.

White‐Light Emission Strategy of a Single Organic Compound with Aggregation‐Induced Emission and Delayed Fluorescence Properties

AbstractA novel white‐light‐emitting organic molecule, which consists of carbazolyl‐ and phenothiazinyl‐substituted benzophenone (OPC) and exhibits aggregation‐induced emission‐delayed fluorescence (AIE‐DF) and mechanofluorochromic properties was synthesized. The CIE color coordinates of OPC were directly measured with a non‐doped powder, which presented white‐emission coordinates (0.33, 0.33) at 244 K to 252 K and (0.35, 0.35) at 298 K. The asymmetric donor–acceptor–donor′ (D‐A‐D′) type of OPC exhibits an accurate inherited relationship from dicarbazolyl‐substituted benzophenone (O2C, D‐A‐D) and diphenothiazinyl‐substituted benzophenone (O2P, D′‐A‐D′). By purposefully selecting the two parent molecules, that is, O2C (blue) and O2P (yellow), the white‐light emission of OPC can be achieved in a single molecule. This finding provides a feasible molecular strategy to design new AIE‐DF white‐light‐emitting organic molecules.

White-light emission strategy of a single organic compound with aggregation-induced emission and delayed fluorescence properties.

A novel white-light-emitting organic molecule, which consists of carbazolyl- and phenothiazinyl-substituted benzophenone (OPC) and exhibits aggregation-induced emission-delayed fluorescence (AIE-DF) and mechanofluorochromic properties was synthesized. The CIE color coordinates of OPC were directly measured with a non-doped powder, which presented white-emission coordinates (0.33, 0.33) at 244 K to 252 K and (0.35, 0.35) at 298 K. The asymmetric donor-acceptor-donor' (D-A-D') type of OPC exhibits an accurate inherited relationship from dicarbazolyl-substituted benzophenone (O2C, D-A-D) and diphenothiazinyl-substituted benzophenone (O2P, D'-A-D'). By purposefully selecting the two parent molecules, that is, O2C (blue) and O2P (yellow), the white-light emission of OPC can be achieved in a single molecule. This finding provides a feasible molecular strategy to design new AIE-DF white-light-emitting organic molecules.

Mechanofluorochromic materials based on aggregation-induced emission-active boron ketoiminates: regulation of the direction of the emission color changes.

We report a series of mechanofluorochromic (MFC) compounds based on organoboron complexes with aggregation-induced emission (AIE) characteristics. We synthesized a variety of boron ketoiminates and investigated the effect of the substituents on the optical properties by altering the end groups in the compounds. The synthesized boron ketoiminates showed AIE properties and MFC behavior. Interestingly, the hypsochromic and bathochromic shifts of the emission bands individually observed for boron ketoiminates depended on the chemical structures of the end groups. From the X-ray diffraction and differential scanning calorimetry analyses, it was confirmed that the MFC property of boron ketoiminates should be derived from a phase transition between crystalline and amorphous states. In addition, the direction of the peak shifts of the emission bands was controlled by the degree of steric hindrance of the end group.

Effect of stacking mode on the mechanofluorochromic properties of 3-aryl-2-cyano acrylamide derivatives

Three structurally simple 3-aryl-2-cyano acrylamide derivatives (o-MPCPA, m-MPCPA and p-MPCPA) were synthesized, which exhibited different optical properties due to their distinct face-to-face stacking mode.

Mechanofluorochromic properties of β-iminoenolate boron complexes tuned by the electronic effects of terminal phenothiazine and phenothiazine-S,S-dioxide

β-Iminoenolate boron complexes bearing phenothiazine exhibited high-contrast mechanofluorochromic behavior compared with that containing a phenothiazine-S,S-dioxide unit.

Fine-tuning the mechanofluorochromic properties of benzothiadiazole-cored cyano-substituted diphenylethene derivatives through D–A effect

We synthesized three new benzothiadiazole-cored cyano-substituted diphenylethene derivatives (PT-OMe, PT-H, and PT-CF3) with different methoxy, hydrogen, and trifluoromethyl end groups, and the synthesis confirmed by standard spectroscopic methods. These end groups endowed them with different donor–acceptor (D–A) effects, and they provide them with a peculiar and completely opposite mechanofluorochromic property. Red-shifted mechanofluorochromic features were found in the PT-OMe and PT-H compounds, while on the contrary, PT-CF3 showed blue-shifted mechanofluorochromic behavior. The mechanofluorochromic mechanism was explored and attributed to the metastable state of the ground compounds and the crystalline-amorphous phase transformation between the original and ground states. Moreover, these derivatives showed reversible significant mechanofluorochromic properties and reproducibility between ground and annealed states, making them promising stimuli-responsive and smart luminescent materials for mechanosensors, fluorescence switches and light-emitting device applications. The introduction of the D–A effect strategy demonstrated in this work would provide a new path to fine tune the optical features of mechanofluorochromic materials with unique and diverse fluorescent properties.

Mechanofluorochromic behaviors of β-iminoenolate boron complexes functionalized with carbazole

New β-iminoenolate boron complexes exhibit different mechanofluorochromic properties due to the excimer and monomer transformation.

A new organic far-red mechanofluorochromic compound derived from cyano-substituted diarylethene

A new cyano-substituted diarylethene derivative (R-NH2) with reversible far-red mechanofluorochromic property was synthesized and confirmed by standard spectroscopic methods. To the best of our knowledge, the 684 nm red-shifted wavelength of the ground R-NH2 is the longest wavelength that has appeared in the literature. The mechanofluorochromic mechanism was investigated by small and wide-angle X-ray scattering and was ascribed to the destruction of crystalline structure. More in-depth study by infrared spectra and time-resolved emission-decay behaviors showed that the changes of C–H out-of-plane bending vibrations in aryl group of the compound and the obvious increase of fluorescence lifetime might be the fundamental reasons. The synthetic strategy reported here can be extended to prepare more and more long-wavelength emission mechanofluorochromic materials, which can broaden the scope of application of such materials and for thoroughly understanding the mechanofluorochromic mechanism.

Synthesis of Carbazole‐Type D‐π‐A Fluorescent Dyes Possessing Solid‐State Red Fluorescence Properties

AbstractCarbazole‐type donor‐π‐acceptor (D‐π‐A) fluorescent dyes (SO1 and SO2), each containing a diphenylamino system as an electron‐donating group and a nitro moiety as an electron‐accepting group, have been designed and synthesized, and their photophysical properties in solution and in the solid state have been investigated. The absorption and fluorescence properties of SO1 and SO2 in solution are similar, and both dyes exhibited moderate fluorescence quantum yields. In the solid state, however, the dye SO2, with a butyl substituent on the carbazole ring, exhibited red fluorescence at around 620 nm, whereas the dye SO1, with no substituent on the carbazole ring, did not exhibit these solid‐state fluorescence properties. Furthermore, the dye SO2 exhibited weak mechanofluorochromic (MFC) properties: grinding of as‐recrystallized dyes induces slight bathochromic shifts of the fluorescence excitation and emission maxima. To elucidate the effects of molecular and crystal structures on the solid‐state fluorescence properties, we performed semiempirical molecular orbital calculations (PM3 and INDO/S) and single‐crystal X‐ray structural analysis. The X‐ray crystal structures of SO1 and SO2 demonstrated that a continuous intermolecular π‐stacking between the fluorophores was observable in the crystal structure of SO1, but not in that of SO2. The MO calculations revealed that SO1 and SO2 have similarly large dipole moments in the ground state (μg ≈ 8 D). The relationship between the observed solid‐state photophysical properties and the molecular and crystal structures of the carbazole‐type D‐π‐A fluorescent dyes are discussed on the basis of experimental results and MO calculations. It is found that the formation of a continuous intermolecular π‐stacking between the fluorophores causes a drastic fluorescence quenching in the solid state and that D‐π‐A fluorescent dyes with very large dipole moments can reduce the MFC properties, due to strong dipole–dipole interactions between the fluorophores in the solid state.

Mechanofluorochromism in Organic Donor-Acceptor Dyes

The authors report the synthesis of a series of carbazole-based donor-acceptor dyes and the characterization of their mechanofluorochromic properties. Utilizing mechanical stimuli to modulate the photophysical properties of materials by reorganization of intermolecular interactions could prove to be a powerful concept in materials design. Potential applications ranging from rewritable materials to electroluminescent devices could be envisioned.