Photoswitching an Isolated Donor-Acceptor Stenhouse Adduct

Area of Science:

• Photochemistry
• Supramolecular Chemistry
• Physical Chemistry

Background:

• Donor-acceptor Stenhouse adducts (DASAs) represent a new class of photoswitching molecules.
• DASAs exhibit notable fatigue resistance and synthetic tunability, making them attractive for various applications.
• Understanding their photochemical behavior in isolation is crucial for designing advanced molecular switches.

Purpose of the Study:

• To characterize the photocyclization reaction of isolated, charge-tagged DASA molecules using tandem ion mobility mass spectrometry and laser excitation.
• To investigate the wavelength-dependent response of DASAs within the 450-580 nm range.
• To elucidate the multi-photon mechanism and thermal reversibility of DASA photocyclization in the gas phase.

Main Methods:

• Tandem ion mobility mass spectrometry (IM-MS) was employed to isolate and study charge-tagged DASA molecules.
• Laser excitation across the 450-580 nm spectrum was used to induce photochemical reactions.
• Multireference perturbation theory calculations were performed to support experimental observations of electronic transitions.

Main Results:

• The experimental maximum response for photocyclization was observed at 530 nm, aligning with theoretical calculations predicting the S₁ ← S₀ transition maximum at 533 nm.
• Gas-phase photocyclization was found to require absorption of at least two photons.
• The reaction proceeds via initial Z-E isomerization, followed by a second photon-induced E-Z isomerization and a 4π-electrocyclization, with thermally reversible cyclization facilitated by collisional excitation.

Conclusions:

• The study provides a detailed mechanistic understanding of DASA photocyclization in the gas phase.
• The findings confirm the multi-photon nature of the reaction and highlight its thermal reversibility.
• This research contributes to the fundamental knowledge of photoswitching molecules and their potential applications.