Multistimuli-Responsive Squaraine Dyad Exhibiting Concentration-Controlled Vapochromic Luminescence

Area of Science:

• Organic materials science
• Supramolecular chemistry
• Photophysics

Background:

• Stimuli-responsive organic materials with tunable luminescence are crucial for sensing, data security, and displays.
• Controllable luminescence in organic materials enables advanced technological applications.

Purpose of the Study:

• To design and synthesize a multistimuli-responsive squaraine dyad (SQ-d) with polymorphic luminescence.
• To investigate the concentration-controlled vapochromic behavior of SQ-d.
• To explore the potential applications of SQ-d in information encryption and vapor sensing.

Main Methods:

• Rational design and synthesis of a squaraine dyad (SQ-d) featuring two squaraine moieties and an ethylene linker.
• Investigation of luminescence switching triggered by solvent vapor, heat, and shear force.
• Analysis of single-crystal structures and photophysical properties to elucidate emission mechanisms.

Main Results:

• The synthesized SQ-d exhibited reversible luminescence switching in response to multiple stimuli.
• A novel concentration-controlled vapochromic behavior was observed, with distinct green and yellow emissions induced by varying chloroform vapor concentrations.
• Two distinct crystallization-induced emission enhancement processes were identified as the origin of the observed vapochromism.
• The green and yellow emissions were attributed to zigzag and H-type π-π stacking modes, respectively.

Conclusions:

• The study presents the first report on vapor concentration-dependent phase transitions in organic vapochromic luminophores.
• The developed SQ-d material demonstrates significant potential for creating prototypes for information encryption and vapor sensing.
• The findings highlight the importance of molecular design in achieving controllable luminescence and stimuli-responsive behavior in organic materials.