Efficient Electron Delocalization Mediated by Aromatic Homoconjugation in 7,7-Diphenylnorbornane Derivatives

Abstract

Efficient electron delocalization by aromatic homoconjugated 7,7-diphenylnorbornane (DPN) in alternated homoconjugated-conjugated block copolymers and reference compounds is revealed by photophysical and electrochemical measurements. The synthesis of the polymers was achieved by Suzuki polycondensation reaction. Effective electron delocalization by DPN is demonstrated by the significant red shifts observed in the absorption and emission spectra and the variation of the energy band gap of the polymers and monomeric model compounds in comparison to a series of oligophenylenes used as references (p-quaterphenyl, p-terphenyl, and biphenyl). The electron delocalization is also clearly demonstrated by the lower oxidation potential measured for homoconjugated model compound in comparison to p-terphenyl. The results show that the electron delocalization caused by two homoconjugated aryl rings is comparable to the effect produced by one conjugated aryl ring.

Electron Delocalization in Homoconjugated 7,7‐Diarylnorbornane Systems: A Computational and Experimental Study

“…According to these data, the effect of two homoconjugated phenyl rings on the HOMO-LUMO energy gap is similar to that caused by one conjugated phenyl ring because the l max of 14 and p-terphenyl (272 vs. 274 nm) and 15 and p-quaterphenyl (295 nm vs. 292 nm) are very similar. [28] In this occasion, TD-DFT calculations assign the observed UV/Vis absorptions to the HOMO!LUMO vertical transitions as well, that is a p-p* transition. The shape of the molecular orbitals is similar to those of the previously discussed systems with the remarkable difference that the HOMO is practically localized in the biphenyl or p-terphenyl fragment with negligible coefficients in the adjacent phenyl groups (Figure 8).…”

“…[28] Comparison of these data with the l max of biphenyl (247 nm), p-terphenyl (274 nm), and p-quaterphenyl clearly demonstrates the effect of electron delocalization by homoconjugation. Thus, the l max of biphenyl is red-shifted by 25 nm when two homoconjugated subunits are attached at the para positions (compound 14).…”

Homoconjugation in poly(phenylene methylene)s: A case study of non-π-conjugated polymers with unexpected fluorescent properties

“…Previously it has been proposed that π‐orbitals of aromatic groups separated by a methylene group (or other groups with comparable geometry) can overlap – a phenomenon which is rarely considered – and hence establish a conjugation over two CC single bonds. This phenomenon is termed homoconjugation .…”

Naphthalene-based oligothiophene-stacked polymers

“…[1][2][3] Recently, a new type of conjugated polymer that exhibits through-space interactions of pelectron systems has been developed. Poly(dibenzofulvene)s, 4-11 7,7-diarylnorbornane-containing conjugated polymers, 12,13 cyclophanecontaining polymers and face-to-face ferrocene polymers [36][37][38] have been synthesized, and their optical and electrochemical properties have been studied in detail. Polymers with layered aromatic rings and p-electron systems have also been investigated; [39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] for example, Chen et al 53 recently reported the synthesis and formation of a twodimensional assembly of polymeric ladder phanes containing face-toface p-electron systems.…”