Micro Raman Investigation of the Photodimerization Reaction of 9-Cyanoanthracene in the Solid State

The classic photodimerization reaction of 9-cyanoanthracene in the solid state has been studied by means of Raman microscopy, analyzing the time evolution both of the molecular and of the lattice phonon spectra from the reactant to the product. This has allowed us to verify that the formation of the dimer crystal structure always takes place with some delay with respect to the onset of the chemical reaction, as already observed in another crystal to crystal photoreaction.(1) This evidence points to a phenomenon of reconstructive phase transition.(2) The kinetic analysis of the spectroscopic data confirms the previous hypothesis of an autocatalytic mechanism for the process.