This award provides partial support for the development of a transient infrared spectrometer. Radiation-induced macromolecular synthesis and modification is critical to many technologies, ranging from combinatorial processes that involve site specific, chromophore-induced polymer photodegradation as the activating step to imaging, lithography, stereolithography, and a variety of rapidly drying printing/coating systems. Understanding the mechanisms of energy and electron transfer occurring in macromolecular assemblies is an important component of this work, as virtually every type of photoinduced reaction involves either energy transfer or electron transfer as an elementary step. The ability to monitor the kinetics of such processes is necessary to understand, and control, chemical events in materials ranging from polypeptide assemblies to photoactivated synthetic drugs. This project includes ongoing collaborations involving two senior faculty who, respectively, carry on broad programs in polymer photochemistry, stereolithography and three dimensional imaging, and on photoprocess dynamics, as well as a program focussing on studying electron transfer processes in rationally synthesized polypeptide assemblies. The instrumentation will be used to study photoinduced processes by monitoring the appearance and /or disappearance of infrared absoptions within the sub-microsecond time domain. In general, the instrument will employ laser flash photolysis to produce reactive intermediates in small molecules and films of macromolecules, and will use infrared absorption spectroscopy for their kinetic analysis. When constructed, the instrument will allow mechanistic studies to be conducted of the initiation steps of polymer photodegradation processes in real time, and provide direct assessment of the chemical reactions leading to changes in polymer properties. The instrument will also be used to analyze photoinitiator systems, to develop new reactive functionalities for the modification of polymer thin films, and to develop new imaging methodology. Other uses include the study of proton coupled electron transfer (PCET) reactions which play an important role in biological energy conversion, but whose mechnisms remain poorly understood. These studies will examine the role of a hyrogen-bonded peptide interface in controlling the rates of photoinduced electron-transfer in synthetic proteins by monitoring the kinetic response of the IR signals occurring within the amide I (1630 - 1700 cm-1) and amide II (1510 - 1560 cm-1) regions of the spectrum. Finally, the instrument will be used to study the photoinduced dissociation of NO from Fe(II) and Co(II) porphyrins. In these experiments, the amount of M-NO bond breaking leading to free NO production can be monitored by the loss of intensity of the M-NO absorption in the 5.87-6.55 um (1525-1690 cm-1) region (metal-dependent) and the growth of intensity at the NO bond stretching frequency 5.37um (1860 cm-1).
In summary, the instrument will, as appropriate, be used to instantaneously evaluate the properties of formed chemical species, improve strategies to site isolate reactive entities as they are formed, understand polymer photodegration, and examine the kinetics of a variety of photoinitiated events. The constructed instrument will be tested using newly synthesized polymer systems such as styrenes, polyesters and other polymers containing chromophores for which the photochemistry has been studied in detail in solution. %%% ***
