Facile preparation and fluorescence properties of a soluble oligopyrrole derivative

Synthesis, Crystal Structure, and Photoluminescent Properties of 3,3',4,4'-Tetraethyl-5,5'-divinyl-2,2'-bipyrrole Derivatives

Photoluminescent divinylbipyrroles were synthesized from 3,3′,4,4′-tetraetyl-2,2′-bipyrrole-5,5′-dicarboxaldehyde and activated methylene compounds via aldol condensation. For mechanistic clarity, molecular structures of Meldrum’s acid- and 1,3-dimethylbarbituric acid-derived divinylbipyrroles were determined by single-crystal X-ray diffraction. Photoluminescent properties of the synthesized divinylbipyrroles in dichloromethane were found to be dependent on the presence of electron withdrawing groups at the vinylic terminal. The divinylbipyrroles derived from malononitrile, Meldrum’s acid, and 1,3-dimethylbarbituric acid showed fluorescent peaks at 553, 576, and 602 nm respectively. Computational studies indicated that the alkyl substituents on the bipyrrole 3 and 3′ positions increased energy level of the highest occupied molecular orbital (HOMO) compared to the unsubstituted derivatives and provided rationale for the bathochromic shift of the ultraviolet-visible (UV-Vis) spectra compared to the previously reported analogs.

Stable 5,5'-Substituted 2,2'-Bipyrroles: Building Blocks for Macrocyclic and Materials Chemistry

The preparation and characterization of a family of stable 2,2'-bipyrroles substituted at positions 5 and 5' with thienyl, phenyl, TMS-ethynyl, and vinyl groups is reported herein. The synthesis of these new bipyrroles comprises three steps: formation of the corresponding 5,5'-unsubstituted bipyrrole, bromination, and Stille or Suzuki coupling. The best results in the coupling are obtained using the Stille reaction under microwave irradiation. The new compounds have been fully characterized by UV-vis absorption, fluorescence, and IR spectroscopies and cyclic voltammetry. X-ray single-crystal analysis of four of the synthesized bipyrroles indicates a trans coplanar geometry of the pyrrole rings. Furthermore, the substituents at positions 5,5' remain coplanar to the central rings. This particular geometry extends the π-conjugation of the systems, which is in agreement with a red-shifting observed for the λ_max of the substituted molecules compared to the unsubstituted bipyrrole. All of these new compounds display a moderate fluorescence. In contrast with unsubstituted bipyrroles, these bipyrroles are endowed with a high chemical and thermal stability and solubility in organic solvents.

The green preparation of poly N-vinylpyrrole nanoparticles

The UV-catalytic preparation of polyN-vinylpyrrole nanoparticles using a green oxidant H₂O₂in the presence of polyvinylpyrrolidone (PVP).