Light-Driven Switching between Intramolecular Proton-Transfer and Charge-Transfer States

Area of Science:

• Photochemistry
• Supramolecular Chemistry
• Organic Electronics

Background:

• Molecular photoswitches are crucial for advanced optical materials.
• Controlling excited-state dynamics is key to designing functional molecules.
• Existing photoswitches often lack independent control over multiple photophysical pathways.

Purpose of the Study:

• To develop a molecular photoswitch with mutually independent excited-state intramolecular proton transfer (ESIPT) and twisted intramolecular charge transfer (TICT) pathways.
• To demonstrate solvent-mediated control over these distinct photophysical processes.
• To achieve tunable fluorescence emission based on triggered photoprocesses.

Main Methods:

• Synthesis of 2-(4'-diethylamino-2'-hydroxyphenyl)-1H-imidazo-[4,5-b]pyridine (DHP).
• Photophysical characterization in various solvents with different hydrogen-bond capacities and polarities.
• Fluorescence spectroscopy and fluorescence lifetime measurements to resolve emission pathways.

Main Results:

• DHP exhibits independent ESIPT and TICT pathways.
• Solvent properties precisely control the activation of ESIPT, TICT, or both.
• Achieved normal, tautomer, and TICT emissions, including triple emission, resolved by fluorescence lifetime.

Conclusions:

• Solvent-dependent control over DHP's photophysical pathways is demonstrated.
• The molecule offers tunable fluorescence properties for potential applications in sensors and optical devices.
• Methoxy derivative studies confirmed the structure-property relationships.