Synthesis, Optical, and Electronic Properties of Soluble Poly-p-phenylene Oligomers as Models for Molecular Wires

• Published in: Journal of the American Chemical Society Vol. 131; no. 5; pp. 1780 - 1786
• Main Authors: Banerjee, Moloy, Shukla, Ruchi, Rathore, Rajendra
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 11.02.2009; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Physical Sciences; Science & Technology; ELECTROCHEMISTRY; ENERGY; CATION-RADICALS; STRUCTURAL-CHARACTERIZATION; POLY(P-PHENYLENE); ABSORPTION-SPECTRA; TRANSITIONS; SOLID-STATE; CHARGE; CONJUGATED OLIGOMERS
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja805102d

A homologous series of soluble poly-p-phenylenes containing up to eight phenylene moieties (PP 2 −PP 8 ) with branched iso-alkyl (or bis-n-alkylmethyl) groups has been synthesized and the structure−property relationship with regards to various optical and electronic properties established. All electronic and optoelectronic properties of poly-p-phenylenes followed a 1/n relationship (where n is number of phenylene moieties) with the increasing number of phenylene moieties. The low-energy electronic transition of the PP 2 −PP 7 cation radicals, generated either by laser-flash photolysis or by chemical oxidation, varied as well according to the inverse (1/n) relationship. The observed inverse relationship of all measured electronic and optoelectronic properties against the increasing number of phenylene units in various PP n ’s, as well as X-ray crystallography of both neutral and a cation-radical salt of a representative tetra-p-phenylene oligomer allows us to demonstrate that the effective conjugation length in poly-p-phenylenes is, in part, controlled by the increasing number of interactions of ortho hydrogens which may prevent simultaneous planarization of the continuous arrays of a large number of phenylene moieties.