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Linkage Isomerization via Germinate Cage or Biomolecular Mechanisms: Time-Resolved Investigations of an Oranometalic Photochrome



Edwin J. Heilweil


The extent of the photoinitiated linkage isomerization of dicarbonyl(3-cyanomethylpyridine-kappa-N3)(eta-5-methylcyclopentadienyl)manganese (4) to dicarbonyl(3-cyanomethylpyridine-kappa-CN)(eta-5-methylcyclopentadienyl)-manganese (5) was examined by time-resolved infrared spectroscopy (TRIR) on picosecond to microsecond timescales in room temperature isooctane to determine the extent the isomerization occurs as a geminate cage rearrangement. We previously reported that a substantial part of the conversion between 4 and 5 must be a bimolecular reaction between a solvent coordinated dicarbonyl(eta-5-methylcyclopentadienyl)manganese (3) and uncoordinated 3-cyanomethylpyridine. For the purpose of designing a molecular device, it is desirable for the photoisomerization to occur in a geminate cage reaction because the faster the isomerization, the less opportunity for side reactions to occur. In this work, assignments of transients are identified by comparison with transients observed for model reactions. Within 100 microseconds after photolysis of 4 in isooctane, no 5 is observed. Instead, the solvent coordinated 3 is observed within 25 picoseconds after irradiation. The formation of 5 is observed only in the presence of 9 millimolar 3-cyanomethylpyridine but not until 10 microseconds to 50 microseconds after irradiation of 4. Within the limits of detection, these results indicate the conversion of 4 to 5 occurs exclusively via a bimolecular reaction of 3-cyanomethylpyridine with solvent coordinated 3 and not a geminate cage reaction between 3-cyanomethylpyridine and the 3 fragment.
Proceedings Title
Time Resolved Vibrations Spectroscopy 2015
Conference Dates
June 21-26, 2015
Conference Location
Madison, WI


Photoswitch dynamics, geminate recombination, bimolecular reaction, solvation, linkage isomerization, time-resolved infrared, ultrafast spectroscopy


Heilweil, E. (2015), Linkage Isomerization via Germinate Cage or Biomolecular Mechanisms: Time-Resolved Investigations of an Oranometalic Photochrome, Time Resolved Vibrations Spectroscopy 2015, Madison, WI (Accessed February 25, 2024)
Created March 25, 2015, Updated February 19, 2017