s-dipentacene: Structure, spectroscopy, and temperature- and pressure-dependent photochemistry

We report the synthesis, characterization, spectroscopy, and photochemistry of s-dipentacene (see Figure 1). The symmetric addition product dimer of p entacene (s-dipentacene) is formed upon irradiation of a solution of pentac ene. The structure of s-dipentacene was determined by X-ray crystallography . The crystals had a space group symmetry of P (1) over bar with two molecu les per unit cell. One molecule in the unit cell was accompanied by two dic hloromethane molecules of solvation. Photodecomposition of s-dipentacene, d ispersed in a poly(methyl methacrylate) (PMMA) host matrix, to pentacene wa s studied. Spectroscopic evidence shows that this photodecomposition procee ds through a trapped intermediate both at low temperature (similar to 12 K) and at room temperature under high pressure (13 kbar). This intermediate i s assigned as a "broken dimer" of two pentacene molecules trapped in the PM MA host. We previously reported similar results in the photolysis of both d ianthracene and ditetracene at low temperatures, but this is the first repo rt of broken dimer formation at room temperature under high pressure.