Computer Simulation of a Solid-State [2 + 2]- Photodimerisation

Abstract

The solid-state [2 + 2]-photodimerisation of three members of the 2-benzyl-5-benzylidenecyclopentanone (BBCP) family of compounds is simulated. Two empirical parameters, R ₁, and R ₂, are defined, which are calculated from the crystal structures of monomer and dimer compounds. R ₁ is correlated with the tendency of the compounds to crack upon photodimerisation. The rates of reaction and the wavelengths of radiation required to effect reaction can be understood in terms of the geometry of overlap of the two monomeric double bonds that react to form the cyclobutane rings of the dimer molecules. The structural factors governing whether the reactions proceed homogeneously or heterogeneously are examined by using the model of a regular solid solution, with interaction energies calculated with (6- exp) atom-atom non-bonded potentials. The importance of the mechanisms of photon absorption, reaction to form a dimer, and exciton transport in determining the phase characteristics of the reaction is also discussed.

Key Words:

• photodimerisation BBCP potential solid-state computer-modelling