Regulation of aggregation-induced emission color of α-cyanostilbene luminogens through donor engineering of amino derivatives

π-Spacer Engineering: Driving Near-infrared Aggregation Induced-emission and Mechanofluorochromism in Carbazole-biscyanostilbenes

In this study, we report the design and synthesis of two novel carbazole-based bis-cyanostilbenes incorporating phenyl and thiophene π-spacer units to investigate their distinct impacts on photophysical properties. Notably, the thiophene-based derivative exhibits remarkable far-red/near-infrared (NIR) solid-state emission, with an emission peak at 732 nm, which shifts to 750 nm upon mechanical grinding, demonstrating pronounced mechanochromic fluorescence in the NIR region. Although its quantum yield is moderate, the ability to modulate its emission through mechanical stimuli opens exciting opportunities for stimuli-responsive NIR applications. Conversely, the phenyl-based analogue shows excellent solid-state emission at 596 nm, achieving significantly higher quantum yields, due to suppressing π-π interactions. Both compounds also exhibit strong AIE, with the thiophene system emitting at 730 nm and the phenyl-based analogue at 580 nm in the aggregate state. In addition to their optical properties, both derivatives demonstrate remarkable thermal stability and reversible MFC. These intriguing behaviors highlight the critical role of π-spacer engineering in fine-tuning solid-state emission, enhancing stimuli-responsive capabilities, and ensuring robust thermal performance. Overall, our findings provide valuable insights into the design of next-generation NIR-emissive materials, with promising potential for advancing applications in optoelectronics, bioimaging, and smart sensing technologies.

Tuning Photophysical Properties via Positional Isomerization of the Pyridine Ring in Donor-Acceptor-Structured Aggregation-Induced Emission Luminogens Based on Phenylmethylene Pyridineacetonitrile Derivatives

A series of aggregation-induced emission (AIE)-featured phenylmethylene pyridineacetonitrile derivatives named o-DBCNPy ((Z)-3-(4-(di-p-tolylamino)phenyl)-2-(pyridin-2-yl)acrylonitrile), m-DBCNPy ((Z)-3-(4-(di-p-tolylamino)phenyl)-2-(pyridin-3-yl)acrylonitrile), and p-DBCNPy ((Z)-3-(4-(di-p-tolylamino)phenyl)-2-(pyridin-4-yl)acrylonitrile) have been synthesized by tuning the substitution position of the pyridine ring. The linkage manner of the pyridine ring had influences on the molecular configuration and conjugation, thus leading to different photophysical properties. The absorption and fluorescence emission peak showed a bathochromic shift when the linking position of the pyridine ring changed from the meta to the ortho and para position. Meanwhile, o-DBCNPy exhibited the highest fluorescence quantum yield of 0.81 and the longest fluorescence lifetime of 7.96 ns as a neat film among all three isomers. Moreover, non-doped organic light-emitting diodes (OLEDs) were assembled in which the molecules acted as the light-emitting layer. Due to the relatively prominent emission properties, the electroluminescence (EL) performance of the o-DBCNPy-based OLED was superior to those of the devices based on the other two isomers with an external quantum efficiency (EQE) of 4.31%. The results indicate that delicate molecular modulation of AIE molecules could endow them with improved photophysical properties, making them potential candidates for organic photoelectronic devices.