UVM Theses and Dissertations
Format:
Print
Author:
Castonguay, Thomas C.
Dept./Program:
Chemistry
Year:
2004
Degree:
Ph. D.
Abstract:
Several zircomum phosphonates incorporating mixtures of pyrene and methyl groups and having the general formula Zr(O₃PC₁₆H₉)x(O₃PCH₃)₂₋x have been synthesized. These systems were characterized with thermal gravimetric analysis, infrared spectroscopy, and solid-state ³¹P NMR spectroscopy. In addition, a structural investigation was carried out using X-ray powder diffraction, the results of which were corroborated by molecular mechanics calculations. It has been observed that the interlayer spacing of these systems changes in a step-wise manner as the organic content is varied. This observation is in direct contrast to Vegard's law, which states that the interlayer distance varies in proportion to the pendant group content. Another facet of this work entailed the investigation of the photophysical properties that these systems possess. Employing both steady-state and dynamic fluorescence spectroscopy, three distinct kinds of excimers were found to exist in the Zr(O₃PC₁₆H₉)x(O₃PCH₃)₂₋x series.
Moreover, it has been shown that structural factors, particularly the interlayer spacing, playa significant role in determining the type of excimer that can form. Molecular mechanics was used to establish the dimer conformations for each of the excimers. Two of the three excimer types consist of two pyrene molecules that are plane-parallel and separated by 3.4 A; these excimers are referred to as type 3bu and 1bu on account of the number of 'benzene units' that overlap in their respective configurations. The third kind of excimer consists of three pyrene molecules and is hence referred to as the cluster type. Semiempirical calculations employing the INDO 1/S methodology were used to compute the ground and first excited state surfaces for the 3bu and 1bu type excimers. The calculated emission bands for the 3bu and 1 bu excimers are in qualitative agreement with the experimental results. It has also been shown in a similar series consisting of naphthyl and methyl groups Zr(O₃PC₁₀H₇)x(O₃PCH₃)₂₋x that more than one excimer type can occur. Overall, these findings signify the possibility of structural control as well as tunable fluorescence for layered materials.
Moreover, it has been shown that structural factors, particularly the interlayer spacing, playa significant role in determining the type of excimer that can form. Molecular mechanics was used to establish the dimer conformations for each of the excimers. Two of the three excimer types consist of two pyrene molecules that are plane-parallel and separated by 3.4 A; these excimers are referred to as type 3bu and 1bu on account of the number of 'benzene units' that overlap in their respective configurations. The third kind of excimer consists of three pyrene molecules and is hence referred to as the cluster type. Semiempirical calculations employing the INDO 1/S methodology were used to compute the ground and first excited state surfaces for the 3bu and 1bu type excimers. The calculated emission bands for the 3bu and 1 bu excimers are in qualitative agreement with the experimental results. It has also been shown in a similar series consisting of naphthyl and methyl groups Zr(O₃PC₁₀H₇)x(O₃PCH₃)₂₋x that more than one excimer type can occur. Overall, these findings signify the possibility of structural control as well as tunable fluorescence for layered materials.