Donor–Acceptor‐Substituted Oligo(1,4‐phenylene)s

Abstract

Oligo(para-phenylene)s (DAOPPs) 2a -2d (n ¼ 1 -4) with terminal donor -acceptor substitution (D ¼ C 6 H 13 O, A ¼ NO 2 ) were prepared by applying Suzuki cross-couplings for chain extension and end capping. The push -pull effect induces short-reaching polarizations of the chain consisting of conjugated but twisted benzene rings, which was studied by NMR measurements. Electron excitation from the ground-state S 0 to the more planar first-excited singlet state S 1 is combined with a strong intramolecular charge transfer (ICT), which is documented by the red shift of the long-wavelength absorption (chargetransfer band) for short chains (one or two repeat units, n ¼ 1 or 2). The opposite influence of decreasing ICT and increasing conjugation length leads to a bathochromic series (l max (n þ 1) ! l max (n)) with a fast saturation of l max (n). The effective conjugation length n ECL ¼ 4 corresponds to l 1 349 nm. These results are discussed in the context of other oligo(para-phenylene)s (OPPs).

ortho-Phenylene oligomers with terminal push–pull substitution

“…Unfortunately, examples of p-phenylene oligomers with similar substitution are limited, presumably because of the poor solubility of higher p-phenylenes. 48 However, oligomers of amino/nitro-substituted p-phenylenes have been reported up to p-quaterphenyl 53,54 and changes in λ max do not reach saturation at this length, suggesting that the charge-transfer interaction through p-phenylenes is much stronger than in the o-phenylenes. Nevertheless, the observation of a charge-transfer absorption band for oP(DA) 3 suggests moderate delocalization through the o-terphenyl subunits of an o-phenylene oligomer, and is consistent with the small but relatively long-range delocalization (n ecl ≥ 4) of o-phenylenes in general.…”

“…However, they have recently emerged as a new class of helical oligomers. For example, Fukushima and Aida have demonstrated a remarkable o-phenylene octamer that exhibits spontaneous resolution of a helical conformation in the solid state, along with a series of monodisperse o-phenylenes up to the [48]-mer. 26 Our own group has been exploring the electronic structures and conformational behavior of simple o-phenylene oligomers.…”

Star-Shaped Conjugated Systems

“…Thus, an average torsion angle ϕ = 23°, which is characteristic for unsubstituted OP chains, reduces the resonance in a 1,4-sexiphenyl chain ( n = 6) to 50 %. Moreover, an angle ϕ = 55.7° would implicate already for n = 3 a 90%decrease of the resonance energy [ 24 ].…”

Bulk heterojunction solar cells based on a low band gap soluble bisazopyrrole and the corresponding BF2-azopyrrole complex

“…In particular, 4-nitrophenol reacted with 1-bromohexane in the presence of K 2 CO 3 to afford the ether derivative 1. 27 The catalytic hydrogenation of the latter in a Parr apparatus afforded the diamine 2. 28 Compound 2 reacted subsequently with NaNO 2 / aqueous HCl at temperature 0-5 C to yield the diazonium salt 3.…”