Synthesis of D–A–A and D–A–D Pyrimidine π‑Systems Using Triorganoindium Reagents: Optical, Vibrational, and Electrochemical Studies

A series of donor–acceptor–acceptor
(D–A–A)
and donor–acceptor–donor (D–A–D) systems
based on a pyrimidine π-spacer with various substituents at
the C-2 position has been successfully prepared. The synthesis involved
site-selective palladium cross-coupling reactions of chloropyrimidines
with triorganoindium reagents and proceed in good yields and with
atom economy. 4-(N,N-Diphenylamino)­phenyl
was chosen as the donor group and thien-2-yl dicyanovinylene as the
acceptor one. The optical, vibrational, electrochemical, and density
functional theory (DFT) calculations of these molecular systems were
analyzed, and experimental values show the important role of the substituents
at the C-2 position of the pyrimidine with stronger electron accepting
ability, absorption in a wide range of UV/vis, acceptable fluorescence
lifetime, and effective intramolecular charge transfer (ICT) properties.
The ICT was observed in both series by the bathochromic shift on increasing
the polarity of the solvent. In addition, DFT calculations found lower
lowest unoccupied molecular orbitals of D–A–A molecules
that suggest good electron ejection and transportation, being good
properties for their application in various organic optoelectronic
devices.