Theoretical investigations of self-organising donor-acceptor aromatic systems

Self-organization or self-assembly is a concept which was introduced some years ago. Hydrogen bonding, electrostatic interactions, van der Waals interactions. donor-acceptor interactions, hydrophilic-hydrophobic interactions and pi-pi interactions are the main types of non-covalent interactions that are responsible for self-organization in biological systems. Self-assembly of naphthalene, anthracene, pyromellitimide and naphthadiimide have been studied. Naphthalene and anthracene are electron rich systems whilst pyromellitimide and naphthadiimide are electron deficient systems. Since, all of these molecules contain aromatic rings, their self-organization is mainly based on aromatic interactions and donor-acceptor interactions. Molecular mechanics and quantum mechanics geometry optimizers were used to build the minimum energy self-assembled molecular systems using Hyperchem Pro computational chemistry package. MM +, Amber2 and Amber94 were the molecular mechanics force fields and AMI, PM3 and MNDO were the quantum mechanical semi-empirical methods. Properties of these molecular systems such as heat of formation, HOMO-LUMO gap (DeltaE), dipole moment and mean polarizability were calculated. The 3D potential energy surfaces of donor-acceptor aromatic systems involving three unit recognition have also been calculated. Plots of heat of formation of molecular systems vs. interplaner distances were having the same shape as Lennard-Jones 6, 12 potentials where there is an energy minimum in a deep potential energy well at a particular interplaner distance. The study shows that these donor-acceptor interactions are very favourable and may also show very interesting optical properties. (C) 2004 Elsevier B.V. All rights reserved.