Excited-State Dynamics of Dithienylethenes Functionalized for Self-Supramolecular Assembly

Area of Science:

• Supramolecular Chemistry
• Photochemistry
• Materials Science

Background:

• Photochromic dithienylethenes (DTEs) are key molecules for molecular switches.
• Quadruple hydrogen-bonding units, like 2-ureido-4[1H]-pyrimidone (UPy), enable self-assembly.
• Controlling supramolecular structures is crucial for tuning material properties.

Purpose of the Study:

• Investigate the photoswitching behavior of UPy-functionalized DTEs.
• Understand the influence of light-induced supramolecular assembly on photochemical processes.
• Differentiate photochemical pathways and parameters for open-form (OF) species.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy
• Ultrafast spectroscopy
• Density Functional Theory (DFT) calculations

Main Results:

• UPy-DTEs form large supramolecular assemblies in the closed form (CF) and small oligomers in the open form (OF).
• Distinct antiparallel (OF-AP) and parallel (OF-P) open-form species were identified.
• A novel photocyclization pathway involving the triplet manifold was observed.
• Photocyclization and intersystem crossing rates are affected by supramolecular assembly, while photoreversion is not.

Conclusions:

• Supramolecular assembly significantly impacts the photochemical response of UPy-DTEs.
• The formation of OF oligomers influences photocyclization and intersystem crossing.
• These findings offer insights into designing responsive photochromic materials.