Synthesis of Pyrene-Anthracene Conjugated Molecular Rods

Fully conjugated pyrene-anthracene-based molecular rods were synthesized by the Horner-Wadsworth- Emmons reaction utilizing potassium tert-butoxide in dry THF. The synthesized rods, which have butylene groups as solubility spacers in the main chain, exhibited good solubility in polar solvents. The solutions of the synthesized pyrene- containing molecular rods exhibited a blue shift in the UV-vis from the absorption maximum due to the presence of the pyrene group in comparison with the dialdehydes. The chemical structure and purity of the synthesized rods were con- firmed by 1 H and 13 C NMR, FAB+, MALDI-TOF, electrospray mass spectra and elemental analysis. The presence of charge-transfer reaction centers in mac- romolecules depends on factors as the composition, the sepa- ration in the interchromophore, the overall dynamical and supramolecular reorganization, and the electronic coupling (1). The synthesis of artificial charge-transfer model systems in which the introduction of simple molecular changes is used to control and tune the magnitude of the electron- transfer parameters became a theme of great interest in the last years. The molecular chains or bridges inside the mole- cule provide endless opportunities, since they determine the structural features and the size of the electronic coupling between the donor and acceptor fragments (2). The modifica- tion of the spacer gives the possibility to introduce a system- atic alteration of separation, orientation, and overlap without affecting the electronic nature of the donor-acceptor pair, for which the coupling is proportional to the overlap of their electronic clouds (3). The electron-transfer processes depend on molecular size and structure, as well as the temperature and the free-energy difference between the donor and accep- tor in donor-bridge-acceptor systems. Currently, monodis- perse and soluble  -conjugated systems with a well-defined length and composition are receiving a growing interest for the design of molecular wires (4) and rods (5), since they can be used as tunable building blocks (6) for nanoscale chemi-