Tuning Emission Wavelength of Polymorphous Crystal via Controllable Alkyl Chain Stacking and Its Vapor‐ and Thermo‐Responsive Fluorescence

• Published in: Chemistry : a European journal Vol. 25; no. 34; pp. 8043 - 8052
• Main Authors: Peng, Lu, Wei, Ruirui, Guo, Yifei, Zheng, Xiaokun, Zheng, Yue, Ding, Yiwen, Xiang, Yu, Tong, Aijun
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 18.06.2019; Wiley Subscription Services, Inc
• Subjects: aggregation-induced emission; alkyl chains stacking; Calorimetry; Chains; Chemistry; Chemistry, Multidisciplinary; Color; Conjugation; Crystal structure; Crystallinity; Crystallography; Crystals; Differential scanning calorimetry; Dimers; Emissions; Fluorescence; Fumigation; Heat treatment; Physical Sciences; polymorph dependent fluorescence; Powder; Recording; Red shift; Science & Technology; Security; Security printing; Stacking; Tuning; vapor- and thermo-stimulation; Vapors; Wavelength; FLUOROPHORES; vapor; COMPLEXES; alkyl chains stacking; RED; polymorph dependent fluorescence; THROUGH-SPACE; LUMINESCENCE; aggregation-induced emission; SUBSTITUENT-DEPENDENT PROPERTIES; ESIPT CHARACTERISTICS; AIE; and thermo-stimulation; RATIONAL DESIGN; vapor- and thermo-stimulation
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201900722

Tuning fluorescence colour of solid‐state materials has become a topic of increasing interest for both fundamental mechanism study and practical applications such as sensors, optical recording and security printing. In this work, a fluorescent colour tuneable molecule BA‐C16 is rationally designed and facilely synthesized by attaching flexible long alkyl chains to 2‐hydroxybenzophenone azine (BA), which shows both aggregation‐induced emission (AIE) and excited‐state intramolecular proton transfer (ESIPT) characteristics. Compared to BA, the simple introduction of long alkyl chains in BA‐C16 leads to an emission wavelength redshift from 542 to 558 nm. This strategy of extending emission wavelength is rarely reported, and is ascribed to the enlarged through‐space π‐conjugation between interplanar molecules in the aggregate of BA‐C16. Three crystals of BA‐C16 are obtained with green, yellowish green and yellow emission. According to characterization by X‐ray crystallography, X‐ray powder diffraction and differential scanning calorimetry, alkyl chains play an important role in inducing different stacking modes of the three crystals, which further leads to polymorph‐dependent fluorescence colour. BA‐C16 exhibits tuneable solid‐state fluorescence upon vapor fumigation, or annealing based on a transition between a “near‐monomer” crystalline state and a “dimer” crystalline state. BA‐C16 is further applied for rewritable fluorescence printing tuned by vapor‐ and thermal‐treatment. Splash of colour: An AIE‐fluorescent colour‐tuneable molecule BA‐C16 is rationally designed and facilely synthesized based on controllable alkyl chain stacking, and is successfully applied for reversible vapor‐ and thermo‐responsive fluorescence printing.