Acid-Responsive Two-photon Absorption Switch via Cocrystal-to-Salt-to-Cocrystal Conversion.

Area of Science:

• Materials Science
• Organic Chemistry
• Photophysics

Background:

• Stimuli-responsive organic cocrystals often face challenges with single-crystal to single-crystal (SCSC) transformations due to structural order disruption.
• Two-photon absorption (TPA) materials are crucial for advanced optical applications, but their solid-state properties require careful design.

Purpose of the Study:

• To develop a novel acid-responsive TPA switch utilizing reversible SCSC transformations.
• To investigate the structure-property relationships governing TPA in organic cocrystals.
• To establish a new paradigm for stimuli-responsive optical switches.

Main Methods:

• Co-crystallization of N-dipyridylanthracene isomers with 1,2,4,5-tetracyanobenzene (TCNB).
• Acid-base treatment (trifluoroacetic acid and triethylamine) to induce cocrystal-to-salt-to-cocrystal transformations.
• Spectroscopic analysis (TPA, photoluminescence quantum yield) and theoretical calculations (DFT).

Main Results:

• The para-N-dipyridylanthracene/TCNB cocrystal exhibits broad-window TPA activity and enhanced solid-state photoluminescence quantum yield (PLQY).
• Positional isomerism of the donor significantly influences molecular coplanarity and donor-acceptor interactions, thereby controlling TPA cross-sections.
• A reversible cocrystal-to-salt-to-cocrystal transformation was achieved, switching TPA characteristics and emission color for over 20 cycles.
• The developed material was successfully applied in display devices and information storage.

Conclusions:

• The study demonstrates an unprecedented acid-responsive TPA switch based on reversible SCSC transformation in organic cocrystals.
• Structure-property relationships governing TPA in cocrystals were elucidated, highlighting the role of molecular arrangement and interactions.
• This work establishes a new platform for designing advanced stimuli-responsive optical materials and devices.