Turn-off mode fluorescent norbornadiene-based photoswitches

Area of Science:

• Organic Chemistry
• Materials Science
• Photochemistry

Background:

• Positive photochromic systems like diarylethenes are used in bioimaging and optical memory.
• The potential of negative photochromic systems for similar applications is underexplored.

Purpose of the Study:

• To investigate negative photochromic molecules for optical memory applications.
• To synthesize and characterize novel norbornadiene-quadricyclane (NBD-QC) photoswitching systems.

Main Methods:

• Synthesis of four NBD-QC molecules with varying pi-electron systems (linear vs. cross-conjugated).
• Photoisomerization studies using UV-Vis absorption spectroscopy.
• Fluorescence quantum yield measurements.
• Evaluation of switching cycles and photochemical reversibility.

Main Results:

• NBD-QC molecules exhibited strong blue shifts in UV-Vis absorption upon photoisomerization to the QC-form.
• Cross-conjugated systems showed high photoisomerization quantum yields (~80%).
• Linearly conjugated NBD-QC compounds displayed significant intrinsic fluorescence (up to 49%), which was quenched in the QC-form.
• The system demonstrated robust, reversible fluorescence switching over multiple cycles.
• All-optical switching between NBD and QC forms was achieved using specific UV wavelengths.

Conclusions:

• The synthesized NBD-QC molecules are promising candidates for negative photochromic applications.
• Reversible fluorescence modulation makes these systems attractive for optical memory devices.
• The ability for all-optical switching enhances their potential for advanced optical data storage.