Research Symposium

BIO

My name is Nicholas MacGilvray, and I am an undergraduate student at Florida State University majoring in Biochemistry and on the pre-med track. I plan on earning my M.D. and becoming a physician. My academic interests include biochemical pharmacology, cell biology, and photochemical reactions.

Photodimerization of 9-Methyl Anthroate

Abstract

Anthracene (1A) photodimerization occurs via the singlet excited state (1A* + 1A) or via triplet-triplet annihilation (TTA, 3A* + 3A*). To determine whether the two pathways involve common singlet excimers, we studied the photodimerization of methyl 9-anthroate (9MeA). 9MeA was selected because on direct excitation it forms three dimers: head to tail at the meso positions (HTm), and head to tail and head to head (HT14, and HH14) involving the meso positions of one partner and the 1,4 positions of the other. Direct excitation (Uranium glass, benzene-d6, 23℃) yielded 84.2% HTm, 13.1% HT14, and 2.72% HH14 at 59.4-93.6% conversions. Under TTA conditions (fluorenone-sensitized, 436 nm), but at lower conversions (6.3-12.3%) similar dimer distributions were obtained, except conversion to HH14 doubled at HTm’s expense. This suggests common excimer precursors with nearly complete equilibration. To assess whether photodimers can interconvert photochemically without reverting to free monomer, efforts to isolate the pure dimers are in progress. HTm (98% pure) has been obtained via column chromatography, but HT14 and HH14 could not be satisfactorily separated by either column chromatography or HPLC. Interestingly, pure HT14, and HH14 were isolated using preparative thin layer chromatography. Their photochemical interconversion will be studied in solution and in glassy media at 77 K. The classic experiments of Chandross and Ferguson at low T encourage us to look for excimer fluorescence from the precursor excimers and possible viscosity dependent excimer equilibration in glassy media.

Keywords: photochemistry, photodimerization, anthracene