The light emitting and absorbing small molecules are interesting for many applications ranging from solar energy conversion to photodynamic therapy. There are many variables that contribute to the intensity, energy and efficiency of absorption and emission including the HOMO/LUMO energy levels, molar absorptivities, excited state lifetimes, geometry changes in the excited state, radiative and nonradiative rates, and others. One of the fundamental goals of photophysical chemists is to understand how molecular structure correlates with these properties. Once structure-property relationships are understood, new molecules can be designed with particular applications in mind. In this thesis, the synthesis, electrochemical and photophysical properties 1,3-bis(2-pyridylimino)isoindoline (BPI) derivatives will be reported and structure property relationships discussed.
In chapter one general concepts and nomenclature associated with the photophysics of small molecules are introduced. The discussion begins with the simplest of light absorbing materials, hydrogen, and then expands to many electron, molecular systems.
Prior to discussing the photophysical properties of BPI derivatives, the synthesis of both the BPI based molecules and platinum BPI complexes will be described in chapter two. To confirm the identity of the compounds all products were characterized by mass spectrometry, x-ray crystallography, elemental analysis and NMR spectroscopy.
Although the parent BPI is non-emissive at room temperature, fluorescence from the dihydroxy substituted BPI derivatives is discussed in chapter 3. The unusual emission from these compounds is attributed to an excited state proton transfer as supported by the large apparent Stokes shift (6600 cm −1) between absorption and emission, the lack of emission from the alkoxy substituted BPI and the large changes in lifetime/efficiency in deauterated methanol (MeOD).
In chapter four, the photophysical and electrochemical characterization of a series of platinum(II) complexes of the form (N
N)PtX where N
N isan assortment of substituted 1,3-bis(2-pyridylimino)isoindolate ligands and X represents various anionic monodentate ligands is discussed. It has been found that the quantum efficiency of emission for all of the complexes is dictated by the nonradiative rates of deactivation from the excited state. The nonradiative rates of the platinum chloride complexes are found to correlate with the energy gap law. For other PtX complexes the graph of the natural log of the nonradiative rates versus energy of emission was found to be nonlinear. The nature of these nonradiative processes is investigated from temperature dependent studies on the excited state lifetime.
Finally, in chapter five a series of five platinum(II) chloride BPI based complexes with varying degrees of benzanulation are characterized. For this series of molecules, either a blue shift or a red shift in absorption and emission maxima, relative to their respective parent compounds, was observed that depended on the site of benzannulation. Experimental data and first principles calculations suggest that a similar HOMO energy level and a destabilized or stabilized LUMO with benzannulation is responsible for the observed trends. An explanation for LUMO stabilization/destabilization is presented using simple molecular orbital theory. This explanation is expanded to describe other molecules with this unusual behavior.
|Advisor:||Thomspon, Mark E.|
|Commitee:||Brutchey, Richard L., Willner, Alan E.|
|School:||University of Southern California|
|School Location:||United States -- California|
|Source:||DAI-B 71/09, Dissertation Abstracts International|
|Keywords:||Benzanulation, Bis-pyridyliminoisoindoline, Phosphorescence, Platinum(II)|
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