Aryl ring rotation in porphyrins. A carbon-13 NMR spin-lattice relaxation time study
- Arizona State Univ., Tempe, AZ (United States)
Overall tumbling and internal rotational motions in porphyrins bearing meso aryl substituents and, in some cases, flanking alkyl groups at the {beta}-pyrrolic positions have been determined using {sup 13}C spin-lattice relaxation time measurements. In deuteriochloroform solution at 303 K, the overall reorientation of all three porphyrins investigated occurs with diffusion coefficients of approximately 1x10{sup 9} s{sup -1}. In porphyrins with only hydrogen at the {beta}-pyrrolic positions, the meso phenyl rings undergo rotations about their single bonds to the porphyrin with diffusion coefficients of approximately 4x10{sup 9} s{sup -1}. Introduction of methyl substituents at the {beta}-pyrrolic positions adjacent to the phenyl rings reduces these motions, but only to approximately 1x10{sup 9} s{sup -1}. Thus, significant internal motions are present in both types of molecules. These motions occur on the time scale of many photoinduced electron and energy transfer processes in porphyrins covalently linked to electron or energy donors or acceptors through meso aryl groups. Thus, the internal librational motions may affect rates of photoinduced electron and energy transfer, even in relatively `rigid` molecular constructs. 47 refs., 3 tabs.
- DOE Contract Number:
- FG03-93ER14404
- OSTI ID:
- 501885
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Journal Name: Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical Journal Issue: 3 Vol. 101; ISSN 1089-5647; ISSN JPCBFK
- Country of Publication:
- United States
- Language:
- English
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