Intermolecular Interactions in Crystals Modulate Intramolecular Excited State Proton Transfer Reactions

Area of Science:

• Photochemistry
• Solid-state chemistry
• Supramolecular chemistry

Background:

• Proton transfer is vital in chemical and biological systems.
• Excited state intramolecular proton transfer (ESIPT) is key for photostability in hydroxyanthraquinone pigments.
• The surrounding environment critically influences proton transfer dynamics.

Purpose of the Study:

• Investigate how crystalline packing affects photoinduced proton transfer dynamics in dihydroxyanthraquinone (DHAQ) isomers.
• Compare proton transfer in crystalline versus solution phases for DHAQ isomers.
• Understand the role of intermolecular interactions in modulating ESIPT.

Main Methods:

• Studied ESIPT dynamics in single crystals of DHAQ constitutional isomers.
• Compared proton transfer behavior in crystalline and solution phases.
• Analyzed the influence of crystal packing and intermolecular hydrogen bonding on excitonic couplings and reaction pathways.

Main Results:

• Substantial differences in proton transfer dynamics were observed between crystalline and solution phases for 1,4- and 1,5-DHAQ isomers.
• Intermolecular hydrogen bonding in 1,4- and 1,5-DHAQ crystals led to larger excitonic couplings, altering reaction pathways.
• 1,8-DHAQ showed minimal changes, lacking intermolecular hydrogen bonds in the crystal.
• An ESIPT relaxation channel, absent in solution, emerged in the 1,4-DHAQ crystal due to intermolecular interactions.

Conclusions:

• Crystal packing plays a critical role in modulating proton transfer dynamics.
• Molecular packing can be strategically controlled to optimize reaction pathways in solid-state environments.
• Findings provide insights into designing materials with tailored photophysical properties based on crystal structure.