Translational Diffusion and Unstable Conformer Trapping in Glassy Isopentane at 77 K

Area of Science:

• Photochemistry
• Physical Chemistry
• Materials Science

Background:

• Isopentane (IP) glass at 77 K is a common matrix for studying photophysical processes.
• Previous studies suggested IP at 77 K is not viscous enough to trap unstable photoproduct conformers.

Purpose of the Study:

• To investigate diffusional quenching in isopentane (IP) glass at 77 K.
• To examine the photoisomerization of cis- and trans-1,2-di(1-methyl-2-naphthyl)ethene in IP glass.
• To challenge the established understanding of IP's ability to trap unstable conformers.

Main Methods:

• Studying the reduction of triphenylene phosphorescence lifetimes in the presence of quenchers.
• Analyzing fluorescence spectra and lifetimes of specific ethene isomers in IP glass at 77 K.

Main Results:

• Diffusional quenching was confirmed in isopentane (IP) glass at 77 K by observing reduced triphenylene phosphorescence lifetimes.
• Photoisomerization of cis-1,2-di(1-methyl-2-naphthyl)ethene to the trans isomer resulted in the trapping of unstable conformers.
• The viscosity of IP at 77 K was shown to be sufficient for trapping unstable photoproduct conformers.

Conclusions:

• Isopentane (IP) glass at 77 K exhibits diffusional quenching.
• The photoisomerization process leads to the stabilization of previously transient species.
• The findings invalidate prior assertions regarding the limitations of IP as a trapping matrix at cryogenic temperatures.