Pyrene-p-tert-butylcalixarenes inclusion complexes formation: a surface photochemistry study.

Area of Science:

• Supramolecular Chemistry
• Photochemistry
• Materials Science

Background:

• Calixarenes are macrocyclic compounds known for their ability to form inclusion complexes.
• Pyrene is a polycyclic aromatic hydrocarbon frequently used as a probe in photophysical studies.
• Understanding host-guest interactions is crucial for designing functional materials.

Purpose of the Study:

• To investigate the photophysics and photochemistry of pyrene encapsulated within p-tert-butylcalix[n]arenes (n=4, 6, 8).
• To examine the formation of inclusion complexes between pyrene and calixarenes in heterogeneous media.
• To elucidate the photodegradation pathways of pyrene within these host molecules.

Main Methods:

• Diffuse reflectance spectroscopy
• Luminescence spectroscopy
• Luminescence lifetime distribution analysis
• Transient absorption spectroscopy

Main Results:

• Evidence of inclusion complex formation for all three calixarene hosts (n=4, 6, 8).
• Formation of pyrene dimers observed within calix[6]arene and calix[8]arene cavities; only monomers fit in calix[4]arene.
• Detection of pyrene radical cations, trapped electrons, and calixarene phenoxyl radicals.
• Hydroxypyrene identified as the major photodegradation product, with dihydro-hydroxypyrene also formed in larger calixarenes.

Conclusions:

• Calixarene cavity size dictates pyrene aggregation state (monomer vs. dimer).
• Photophysical properties of pyrene are significantly influenced by encapsulation within calixarene hosts.
• Photodegradation pathways involve radical intermediates and hydrogen abstraction, particularly in calix[6]arene and calix[8]arene.