Novel, soluble diphenyl-diketo-pyrrolopyrroles: Experimental and theoretical study

Derivatives of diphenyl-diketo-pyrrolopyrrole, possessing electron-donating or withdrawing groups in the p-position of the phenyl, were synthesized and studied using optical characterization (absorption, fluorescence, time-resolved fluorescence) and quantum chemical calculation. An increase in absorption coefficient >= 10(5) dm(3) mol(-1) cm(-1) was observed using electron-donor groups; a bathochromic shift in both absorption and luminescence peaks was observed as a result of increased conjugation. Soluble derivatives were obtained by the introduction of alkyl groups (by N-alkylation) in the central pyrrolopyrrole unit. Calculated phenyl torsion angles using HF and B3LYP methods showed that the loss of molecule planarity reduced the extent of overlap between the pi-orbitals of the central pyrrolopyrrole unit and phenyls after N-alkylation. This treatment thus reduced both the bathochromic shift and increased absorption coefficient. The presence of the donor or acceptor groups in itself does not influence molecule planarity. (C) 2009 Elsevier Ltd. All rights reserved.