Photochromic bis(thiophen-3-yl)maleimides studied with time-resolved spectroscopy

Area of Science:

• Photochemistry
• Organic Chemistry
• Spectroscopy

Background:

• Bis(thiophen-3-yl)maleimides undergo ring-closure reactions.
• Substituent effects on reaction dynamics are not fully understood.

Purpose of the Study:

• Investigate the excited-state dynamics of three bis(thiophen-3-yl)maleimides.
• Elucidate the influence of thiophene ring substitution on reaction kinetics and product formation.

Main Methods:

• Ultrafast spectroscopy in the visible range.
• Analysis of reaction kinetics and excited-state lifetimes.

Main Results:

• Unsubstituted thiophene rings exhibit long excited-state lifetimes (3 and 15 ns) and low ring-closure yield (<1%).
• Dimethyl substitution leads to faster excited-state decay (16 ps) and partial formation of the ring-closed isomer.
• Dimethyl-substituted imides suggest the existence of two open-isomer conformations.

Conclusions:

• Thiophene ring substitution critically influences excited-state dynamics and reaction pathways.
• Dimethyl substitution promotes ring-closure via a distinct pathway with a shorter-lived excited state.
• The study highlights the complex interplay between molecular structure and photochemical reactivity.