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

Abstract

A joint computational-experimental study has been carried out to analyze the homoconjugative interactions in 7,7-diarylnorbornane (DPN) derivatives. The experimentally observed new bands in their UV/Vis have been accurately assigned by means of TD-DFT calculations. Both experimental data and computations show that aromatic homoconjugation in acyclic systems is an effective mechanism for electron delocalization that resembles the situation described for polyphenylenes and polyenes. The effective homoconjugation length in homoconjugated oligomers is in the range of 6-7 aryl rings. The effect of substituents directly attached to the para carbon atom of the DPN moiety have been also studied. We found that the HOMO→LUMO vertical transitions can indeed be modified by the nature of the aromatic substituents in order to provoke dramatic changes in the electronic properties (i.e., in the absorption spectra) of the studied species.

A Joint Experimental and Computational Investigation on Homoconjugated Push‐Pull Chromophores Derived from 7,7‐Diphenylnorbornane

“…Therefore, electronic communication by homoconjugation can be easily tuned by controlling the electronic nature and positions of the substituents. [26] The results of these investigations confirm that aromatic homoconjugation in acyclic systems is an effective mechanism for electron delocalization with an effective homoconjugation length for homoconjugated oligomers of 6-7 aryl rings. DFT calculations nicely agree with the experimental data and shed light on the electronic delocalization via homoconjugation.…”

“…[21][22][23][24][25][26] One of the advantages of DPNs is that a large variety of different molecules can be prepared following standard and straightforward procedures. The synthesis of these compounds was carried out according to the methodology described previously by us (Scheme 1).…”

“…[19] Very recently, homoconjugated push-pull systems obtained by [2+2] cycloaddition reaction between 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and N,N-dialkylanilino (DAA) (4, Figure 1) or ferrocene-substituted alkynes have been described. [21][22][23][24][25][26] Homoconjugated push-pull systems were synthesized and used for the first time to study the nature of plus polarization 6-31+G(d) basis sets. Aromatic apical homoconjugated compounds derived from 7,7-diphenylnorbornane (DPN) (5c, Figure 2) are a family of interesting derivatives featuring non-conventional electron delocalization within the cofacially arranged aryl groups.…”

“…[21][22][23][24][25][26] Homoconjugated push-pull systems were synthesized and used for the first time to study the nature of plus polarization 6-31+G(d) basis sets. The B3LYP [31] Hamiltonian was chosen because it was proven to provide reasonable UV/Vis spectra for a variety of chromophores [26,32] including organometallic species. Calculations of absorption spectra were accomplished by using the time-dependent density functional theory (TD-DFT) [ 30] method.…”

σ-Hole⋯π and lone pair⋯π interactions in benzylic halides

“…Furthermore, these should be LP⋯π interactions since the σ-holes of the halogens are directed outside the planes of the aromatic rings. 37,[53][54][55] This HOMO−3 → LUMO transition occurs in compound 2 as well. The computed vertical transitions and the corresponding oscillator strengths show a nice agreement with the experimental data (see Table 1).…”