Multi-state Photoswitching in Thienoquinoid-Based Fluorescent Trithiophenes

Area of Science:

• Organic Chemistry
• Photochemistry
• Materials Science

Background:

• Achieving multi-site photoisomerization in conjugated systems while maintaining luminescence is challenging.
• Electronic coupling and nonradiative pathways often hinder sequential switching and emissive behavior.

Purpose of the Study:

• To design and synthesize a methine-bridged trithiophene capable of multi-site photoisomerization with retained luminescence.
• To investigate the photophysical properties and multi-state control of the synthesized compound.

Main Methods:

• Synthesis of a methine-bridged trithiophene with 2,6-dichlorophenyl substituents.
• Photoisomerization studies to generate ZZ, EZ, and EE geometrical isomers.
• Spectroscopic analysis including fluorescence quantum yield and lifetime measurements.

Main Results:

• The compound exhibits three interconvertible geometrical isomers (ZZ, EZ, EE) via photoisomerization.
• Steric hindrance from ortho-chloro substituents suppresses nonradiative relaxation, enhancing fluorescence quantum yield (0.40 for ZZ-isomer).
• Wavelength-selective control over isomer distribution was achieved, differing from thermodynamic equilibrium.

Conclusions:

• The study presents a molecular design for luminescent multi-state photoswitches.
• This strategy is applicable to multi-level optical information processing.
• Molecular geometry significantly influences photophysical properties in conjugated frameworks.