Dimethylcethrene: A Chiroptical Diradicaloid Photoswitch

Area of Science:

• Organic Chemistry
• Photochemistry
• Materials Science

Background:

• Diradicaloid molecules offer unique electronic properties for molecular switches.
• Photochemical switches enable reversible transformations triggered by light.
• Chirality in molecular switches can lead to novel chiroptical functionalities.

Purpose of the Study:

• To synthesize and characterize 13,14-dimethylcethrene as a chiral diradicaloid photochemical switch.
• To investigate the reversible switching mechanism and its impact on electronic and optical properties.
• To evaluate the stability and potential applications of this novel molecular system.

Main Methods:

• Synthesis of 13,14-dimethylcethrene.
• Photochemical and thermal switching experiments.
• Spectroscopic analysis including NMR, UV-vis, and Circular Dichroism (CD).
• Density Functional Theory (DFT) calculations.

Main Results:

• 13,14-dimethylcethrene undergoes reversible conrotatory electrocyclization triggered by specific wavelengths of light (630 nm and 365 nm) or heat.
• The switching process significantly alters electronic parameters like HOMO-LUMO and singlet-triplet (ST) energy gaps, and helical twist.
• Distinct changes in optical and chiroptical properties were observed and monitored spectroscopically.
• Methyl substituents enhance the stability of the closed form and increase the ST energy gap by ~4 kcal mol⁻¹ compared to cethrene.

Conclusions:

• 13,14-dimethylcethrene functions as a robust chiral diradicaloid photochemical switch.
• The methyl groups improve stability and modulate electronic properties, particularly the ST energy gap.
• This system demonstrates the translation of diradicaloid reactivity into a switching function with potential for magnetic switch applications.