Dr. Edwin F. HilinskiAssociate Professor
Ph.D. (1982) Yale University
Research InterestMECHANISTIC STUDIES OF PHOTOCHEMICAL AND THERMAL REACTIONS OF ORGANIC COMPOUNDS IN SOLUTION; TIME-RESOLVED LASER SPECTROSCOPY; PHOTOINDUCED PHENOMENA IN THE SOLID STATE
Many important phenomena that interact to determine the outcome of a chemical reaction occur in the time regime from 10-13 to 10-6 seconds. These dynamic processes include electron and energy transfer, bond dissociation and formation, unimolecular rearrangement, diffusion, and interactions between reactants and between reactant and solvent. Our research primarily focuses on studies of reacting organic molecules and interactions that they have with their environment. A method on which we rely is timeresolved laser spectroscopy. We have focused on studies of reaction intermediates whose lifetimes are as short as 10 ps. Laser systems that produce pulses of light as short as 120 femtosecondsâ€”with wavelength tunability from the ultraviolet through the visibleâ€”provide us with the means to get answers to tantalizing questions about structure and reactivity for species which exist in the subpicosecond time regime. The short-lived intermediates are detected via electronic absorption or emission spectroscopy. We synthesize compounds designed to reveal mechanistic intricacies when probed spectroscopically. Several research areas are highlighted here.
1. Photofragmentations of organic molecules can give rise to a variety of reactive species. Photodissociations of sigma bonds in organic molecules in solution often give fragments formally resulting from bond homolysis and bond heterolysis.
We are investigating the roles of several mechanisms in the formations of radicals and ions from initially populated π, π* excited states. The fragments that are formed also permit studies of their ground-state reactivities.
Photochemical extrusion of relatively stable molecules permits the generation of reactive divalent-carbon containing species known as carbenes. The two unshared electrons on the carbenic center open the possibility for different reactivities through singlet (S) and triplet (T) electronic spin states. We are interested in learning more about how these reactivities are manifested and can be controlled.
Photodissociable molecules that lead to the formation of radicals, ions, and carbenes may be used to probe the structures of reaction environments and large biologically important molecules. We are developing new compounds which can be used as photoaffinity labels.
2. The twisted excited singlet state (1p*) of a polyarylalkene may be considered to be composed of contributions from zwitterionic (I), singly (II), and doubly (III) excited states. Our time-resolved spectroscopic studies have provided evidence for the assignment of the zwitterionic form (I) as the dominant electronic contributor to the lowest 1p* of several substituted tetraphenylethenes. Substituted polyarylethenes are under investigation to evaluate the contributions of I, II, and III to 1p*, which will permit a better understanding of the reactivities of polyarylethenes.
3. Photoinduced electron transfer, involving excitation of groundstate organic electron donor-acceptor complexes, is being studied to learn the roles of orbital symmetries and the effects of heavy atoms on electron-transfer rates in solution.
In our research, we strive to learn how electrons are distributed in these processes and how our results compare with theoretical predictions.