Solid state photochemistry at 4.2 K: The photocyclization of [5] helicene to dihydrobenzoperylene in hpolskii matrices

Abstract

The reversible photocyclization reaction of [5]helicene to dihydrobenzoperylene (DHBP) was studied in the Shpolskii matrices n-pentane and n-hexane at 4.2 K. The well-resolved transitions from the photochemical product are attributed to DHBP, occupying a distinct site in n-hexane. The photoinduced formation of DHBP at 4.2 K was monitored during illumination by sequentially recording fluorescence spectra. The multiplet structure of [5]helicene and DHBP in fluorescence and in phosphorescence in n-pentane were determined by high-resolution total luminescence spectroscopy (TLS). The subsequent dehydrogenation of DHBP to benzoperylene (BP), which occurs rapidly at higher temperatures in fluid media and in the presence of hydrogen acceptors, was found to be inhibited in solid matrices.