STRUCTURAL, ELECTRONIC AND OPTICAL PROPERTIES OF THIOPHENE AND THIENOTHIOPHENE CONTAINING DIKETO-PYRROLO-PYRROLES (DPPs) IN POLAR APROTIC SOLVENTS

Abstract

Thiophene (T) and thienothiophene (TT) containing 2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) compounds were prepared according to the succinic ester route from the corresponding heterocyclic nitrile precursors. As is typical of most DPP pigments, the new compounds showed high thermal stability and could be obtained in pure form as determined by elemental analysis. The bulk properties and molecular structure of the compounds were further characterized by thin film, powder XRD and solid state CP-MAS 13 C NMR. Density functional theory (DFT) and time-dependent (TD) DFT were employed to study the geometric and electronic structures of these molecules in the ground state. The optical properties were investigated by UV-Vis absorption and fluorescence spectroscopies in dimethylsulfoxide (DMSO) and N,N-dimethylacetamide (DMA), which revealed that the absorption maximum of the thiophene diketo-pyrrolo-pyrroles (TDPP) and thienothiophene diketo-pyrrolo-pyrroles (TTDPP) in solution were red shifted up to 25 nm and 60 nm, respectively, relative to Pigment Red 255 (PhDPP), while a new absorption band appeared at longer wavelengths in N-methyl pyrolidone (NMP) and N,N′-dimethylpropylene urea (DMPU) which is ascribed to solvent induced charge transfer (CT) complex. The molecular conformations and absorption spectra of TDPP and TTDPP were characterized by quantum chemical methods in order to better understand the observed behavior.