Theoretical Investigation on the Topochemical Polymerization of Diacetylenes

Abstract

Abstract The solid-state polymerization of diacetylenes (MDA-PBT-PDA) is studied with a concerted reaction model and the calculation method of EHMO-ASED and EHCO-ASED, where MDA = crystalline molecular diacetylenes, PBT = polybutatrienes, and PDA = polydiacetylenes. As the reaction goes on, the symmetry of frontier orbitals inverts at state PBT, HOCO from C 2-antisymmetry to C 2-symmetry and LUCO from C 2-symmetry to C 2-antisymmetry, which means completion of the 1,4-addition. Two necessary conditions must be satisfied for the reaction to take place: 1) the geometric parameters must undergo a series of concerted changes to make the conformation suitable for the intermolecular 1,4-addition, which should overcome an energy barrier Eb ; 2) the symmetry match between the frontier crystal orbitals of the reactant and the product must be satisfied-electrons of the reactant should be excited from HOCO (C 2-antisymmetry) into LUCO (C 2-symmetry), which faces an energy gap E g. At state MDA, there is E g(MDA) ≈ 5...