We report the synthesis, characterization, spectroscopy, and photochemistry of s-dipentacene (see Figure ).
The symmetric addition product dimer of pentacene (s-dipentacene) is formed upon irradiation of a solution
of pentacene. The structure of s-dipentacene was determined by X-ray crystallography. The crystals had a
space group symmetry of P1̄ with two molecules per unit cell. One molecule in the unit cell was accompanied
by two dichloromethane molecules of solvation. Photodecomposition of s-dipentacene, dispersed in a poly(methyl methacrylate) (PMMA) host matrix, to pentacene was studied. Spectroscopic evidence shows that
this photodecomposition proceeds through a trapped intermediate both at low temperature (∼12 K) and at
room temperature under high pressure (13 kbar). This intermediate is assigned as a “broken dimer” of two
pentacene molecules trapped in the PMMA host. We previously reported similar results in the photolysis of
both dianthracene and ditetracene at low temperatures, but this is the first report of broken dimer formation
at room temperature under high pressure.
The process of photochemical hole burning in rigidly coupled polyacenes is discussed.Photochemical mechanisms in these systems are conducive to low temperature spectral hole burning. Several factors which determine the shape and width of spectral holes are discussed. Prospects for use in information storage applications are presented.
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