Synthesis of polyheteroaromatic compounds derived from electron deficient diamines and study of their photophysical properties

Abstract

Two types of polycyclic heteroaromatic molecules were synthesized by the condensation reactions between electron deficient pyrazinophenathrolinediamine and different electron rich/deficient diketones based on the newly developed pyrazinopyrazinephenanthroline based unit. The electrochemical, photophysical, as well as computational studies of these molecules were carried out. The first type of pyrazinopyrazinephenanthroline based molecules, with electron-deficient structures, were employed for the functionalization of carbon nanotubes (CNTs) and the interactions between molecules and CNTs were studied by femtosecond time-resolved transient absorption (fs-TA) spectroscopy. For the second type of pyrazinopyrazinephenanthroline derivatives, with donor-acceptor-type structures, their steady state luminescence properties were studied.

The first type of pyrazinopyrazinephenanthroline based molecules, with electron deficient structures were synthesized and used as the dispersants for both single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) via noncovalent interactions. Preliminary studies from TA spectroscopy showed that the interaction between the molecules and CNTs was not strong, as can be seen from their similar decay kinetics. It is suggested that the interaction between their compounds with MWCNTs is slightly stronger than that with SWCNTs, which can be seen from the more significant change in the decay kinetics upon formation of hybrid.

The second type of pyrazinopyrazinephenanthroline based molecules, with donoracceptor- type structures were synthesized. Their luminescence properties were studied and the results were compared with the pyrazinophenanthroline based compounds. Compounds with pyrazinopyrazine bridges possess lower band gap energies and show significant red shifts in their absorption and emission spectra than their corresponding compounds with pyrazine bridges. Compounds with pyrazine bridges reveals higher quantum yields with longer lifetimes than those compounds with pyrazinopyrazine bridges, which is possibly due to the polarization effects of the nitrogen atoms. Both series of pyrazinopyrazinephenanthroline compounds could be used as the active materials in opto-electronic devices, and the hybrids formed between these molecules and carbon nanotubes may be applied in light harvesting devices.