Protomer-Specific Photochemistry Investigated Using Ion Mobility Mass Spectrometry

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Spectroscopy

Background:

• Protonated molecules can exist as multiple protomers with varying structures.
• Investigating protomer-specific properties is crucial for understanding molecular behavior.

Purpose of the Study:

• To demonstrate the utility of ion mobility mass spectrometry coupled with electronic spectroscopy.
• To investigate protomer-specific photochemistry of protonated 4-dicyanomethylene-2-methyl-6-para-dimethylaminostyryl-4H-pyran (DCMH+) molecules.

Main Methods:

• Utilized tandem ion mobility mass spectrometry (IMMS) with electronic spectroscopy.
• Measured photoisomerization action spectra for different DCMH+ protomers using He, N2, and CO2 buffer gases.
• Performed electronic structure calculations for comparison.

Main Results:

• Three protomers of DCMH+ were distinguished by ion mobility and photoisomerization responses.
• Trans-DCMH+ protomers showed distinct photoisomerization at 420 nm and 625 nm.
• Cis-DCMH+ protomers exhibited no discernible photoisomerization, suggesting fluorescence dominance.

Conclusions:

• Isobaric protomers and isomers can exhibit significantly different photochemical behaviors.
• Isomer and protomer selective techniques are valuable for studying gas-phase protonated molecules.
• The study showcases a powerful approach for probing molecular photochemistry at the protomer level.