Phenothiazine-Based Luminophores with AIE, Solvatochromism, and Mechanochromic Characteristics

Abstract

Aggregation-induced emission (AIE) fluorescent molecules with unique photoelectric properties have received extensive attention due to the wide range of applications. In this work, two novel phenothiazine-based luminophores DPE-PTZ-Cl and DPE-PTZ-CF 3 were designed based on the frontier molecular orbital (FMO) theory and construction strategy of AIEgens. As expected, both of the luminophores displayed typical AIE behavior and realized the spatial separation of FMOs, which was confirmed by the positive solvatochromism behavior. Their AIE properties could be attributed to the twisted three-dimensional (3D) conformation. Such a conformation resulted from “butterfly-like” phenothiazine and a multirotor structure of diphenylethylene. The spatial separation of FMOs originated from the push–pull electronic synergistic effect of the donor–acceptor (D–A) architecture. Interestingly, DPE-PTZ-Cl also showed a rare blue-shifted mechanochromic (MC) luminescence property. Single-crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD) experiments were carried out to reveal that the phase transformation between crystalline and amorphous states was responsible for the peculiar solid-state luminescence phenomenon.

R–D–A and R–D−π–A Structured AIEgens: Relationship between Electronic, Conformational Characteristics and Photophysical Properties

“…As shown in Scheme , phenothiazine-based derivatives DPE-PTZ-CN and intermediate product DPE-PTZ-Cl were facilely synthesized through the Stork enamine reaction, , which were catalyzed by (±)-camphor-10-sulfonic acid. Subsequently, DPE-PTZ-Cl and 4-cyanophenylboronic acid were cross-coupled through the Suzuki reaction to produce DPE-PTZ-PCN in the presence of a palladium catalyst.…”

“…The synthesis steps and structural characterization results of the intermediate product DPE-PTZ-Cl followed our previous work . In detail, 2-chlorophenothiazine (0.93 g, 3 mmol) was dissolved in 20 mL of toluene.…”

“…The synthesis steps and structural characterization results of the intermediate product DPE-PTZ-Cl followed our previous work. 32 In detail, 2-chlorophenothiazine (0.93 g, 3 mmol) was dissolved in 20 mL of toluene. 2,2-Diphenylacetaldehyde (0.79 g, 3 mmol) and (±)-camphor-10sulfonic acid (3 wt %) were added to the solution.…”

“…1 H NMR spectrum (600 MHz, DMSO-d 6 , δ, ppm): 7.88 (d, J = 6 Hz, 2H, Ar in benzonitrile), 7.75 (d, J = 6 Hz, 2H, Ar in benzonitrile), 7.44−7.36 (m, 7H, Ar in phenothiazine), 7.28− 7.17 (m, 3H, Ar), 7.12−7.06 (m, 7H, Ar), 6.91 (t, J = 6 Hz, 1H, N−CH). 13 21,32 which were catalyzed by (±)-camphor-10-sulfonic acid. Subsequently, DPE-PTZ-Cl and 4-cyanophenylboronic acid were cross-coupled through the Suzuki reaction to produce DPE-PTZ-PCN in the presence of a palladium catalyst.…”

“…The twisted multi-rotor groups or propeller-like structures are typical structural features of AIEgens, for example, tetraphenylethylene and triphenylethylene, which are the most common AIE building blocks. − However, these traditional AIE-active fragments are mainly synthesized by the McMurry reaction in somehow violent conditions or with limited yield. , Moreover, the subsequent work of introducing them to new molecules makes the whole synthesis process more complicated. To make up for these shortcomings, in our previous works, the typical Stork enamine reaction was adopted to conveniently introduce diphenylvinyl groups into the new molecular system through the condensation of diphenylacetaldehyde and secondary amine structures. − All of the obtained series of products showed significant AIE property, which provided a convenient way for the construction of AIEgens through introducing a simpler rotor structure. Nevertheless, the reported AIE molecules based on such enamine structures with a simple twisted rotor group are still very rare.…”