Charge transfer through cross-hyperconjugated versus cross-π-conjugated bridges: an intervalence charge transfer study

Abstract

Recently there has been much interest in electron transfer and transport through cross-conjugated molecules as interesting test cases for the interplay between molecular and electronic structure as well as potential motifs in the design of new compounds for molecular electronics. Herein we expand on this concept and present the synthesis and characterization of a series of four organic mixed-valence dyads to probe the effect of the bridge structure on the electronic coupling. The electronic coupling between two triarylamine units could be mediated either by cross-hyperconjugation through a saturated ER 2 bridge (E ¼ C or Si, R ¼ alkyl or silyl group), or via a cross-conjugated p-system. The aim of the study is to compare the electron transfer through the various saturated bridges to that of a cross-p-conjugated bridge. The electronic coupling in these mixed-valence compounds was determined by analysis of intervalence charge transfer bands, and was found to be in the range of 100-400 cm À1 . A complementary DFT and TD-DFT study indicated that the electronic coupling in the dyads with saturated ER 2 segments is highly conformer dependant. Furthermore, the calculations showed that two types of interactions contribute to the electronic coupling; a through-bond cross-(hyper)conjugation mechanism and a through-space mechanism. Taken together, these findings suggest the possibility for new architectures for molecular electronics applications utilizing cross-hyperconjugation through properly selected saturated segments which have comparable electron transfer characteristics as regular cross-p-conjugated molecules.

Cross‐Conjugated π‐Scaffolding with Pendant N‐Heterocyclic Metal‐Binding Sites

“…Although crossconjugation has been a topic of intense research efforts, [5][6][7][8][9][10][11][12][13][14] cross-conjugated systems with N-heterocyclic metal-fragment complexing sites are relatively rare. The Pd-catalysed cross-coupling reactions of the corresponding heterocyclic dibromoolefins and terminal alkynes provide convenient access to the new ligand systems.…”

“…Although crossconjugation has been a topic of intense research efforts, [5][6][7][8][9][10][11][12][13][14] cross-conjugated systems with N-heterocyclic metal-fragment complexing sites are relatively rare. Although crossconjugation has been a topic of intense research efforts, [5][6][7][8][9][10][11][12][13][14] cross-conjugated systems with N-heterocyclic metal-fragment complexing sites are relatively rare.…”

Synthesis and Cyclization‐Induced Charge Transfer of Rectangular Bisterthiophenesiloxanes

“…These emission peaks are similar with terthiophene. In addition, a distinguishingly broad and structureless emission around 516 nm, which cannot be found in emission of terthiophene in CH 2 Cl 2 solution (Figure S14, Supporting Information), could be ascribed to an ICT transition . Moreover, the evident ICT emission can also be found in the film states.…”

“…In addition, ad istinguishingly broad and structurelesse mission around5 16 nm, which cannot be found in emission of terthiophene in CH 2 Cl 2 solution (Figure S14, Supporting Information), could be ascribed to an ICT transition. [20] Moreover,t he evident ICT emission can also be found in the film states. Comparing to the p-p*t ransition emission, the relative intensity of ICT emission in the filmi sl ower than that in CH 2 Cl 2 solution, which may be caused by the aggregation-induced quenching in the solid states.I na ddition, the emission at approximately 516 nm is strongly quenched in the polar acetone, supporting the assignment of it to the ICT emission again.T of urtherc onfirm the ICT character,t he transient photoluminescence (PL) decay characteristics of DSiTh is measured in the solution as shown in Figure 2b.O bviously,t he emission at 516 nm shows as lower decay with al onger lifetimeo f1 3.08 ns than that at 405 and 430 nm with lifetimes of 3.05-3.11ns.…”

Conformation‐Determined Through‐Bond versus Through‐Space Electronic Communication in Mixed‐Valence Systems with a Cross‐Conjugated Urea Bridge

“…[15] Very recently, Hammarstrom and Ottosson and co-workers examined the electronic communication between two triarylamines through the crossconjugated 1,1-diethynylalkene (Figure 1, E) and the crosshyperconjugated 2,2-diethynyl-1,1,1,3,3,3-hexamethyltrisilane (Figure 1, F) bridge. [16] In addition to these advances, cross-conjugated molecules have recently received increased interest in single-molecule electronics with quantum interference effects, from both a theoretical and experimental perspective. [17] We report herein on the first MV system with diarylurea as a cross-conjugated bridge.…”