Remote Communication between Charge Centers and Hydrogen-Bonding Sites: Possibility for a Signal Transducer?

Abstract

Signal enhancement from a reaction center to a hydogen‐bonding site occurs when they are separated by an azo linker (see schematic representation). A computational study has shown that the binding of ammonia to a pyrrole unit in an iminium compound increases as the length of the azo group between the two sites increases. This surprising result is explained in terms of resonance effects and the larger electron‐withdrawing power of longer azo linkers.

Theoretical Study of the Remote Control of Hydrogen Bond Strengths in Donor–Bridge–Acceptor Systems: Principles for Designing Effective Bridges with Substituent Tuning

“…Table 3 presents the calculated binding energies of three‐component systems with ((CHCH) n C(CN)C(CN)) x bridges, where n = 1–4, x = 1–2. It can be seen that these bridges do not result in significant signal reduction as for pure carbon bridges (ΔΔ E b(P−N) of three‐component systems with (CHCH) n ( n = 1–4) decreased by more than 2 kcal mol −1 6a). Therefore, the C(CN)C(CN) unit can greatly improve the signal reduction effect of a pure carbon bridge just as with an azo unit.…”

“…We have already demonstrated that insertion of a NN unit into the repeating unit of a bridge, ((CHCH) n –NN), dramatically improves the signal maintenance of carbon bridges 6a. Because a (C(CN)C(CN)) n bridge is significantly better than a (CHCH) n bridge, it is of interest to find out whether the C(CN)C(CN) unit can generate a similar effect as with NN insertion.…”

“…weaker signal transduction). However, it was found that long azo bridges provided good signal maintenance in our three‐component systems 6a. Systematic studies of protonated three‐component systems with hybrid bridges containing C and N atoms lead to a simple working model to rationalize the calculated results: an electron was donated from the HOMO of pyrrole to the combined LUMO of the other two components, the bridge‐iminium moiety (Figure 2).…”

Investigations on the electronic effects of the peripheral 4′-group on 5-(4′-substituted)phenylazo-8-hydroxyquinoline ligands: zinc and aluminium complexes

“…In fact, in both cases the 8-hydroxyquinoline fragment is coplanar with the diazo moiety, giving rise to a basically flat molecule, with mean torsion angles N-N-C Ph -C Ph of 0.4(6) and 3.9(2)°, respectively. In compound I the N(CH 3 ) 2 substituent is also coplanar with the rest of the molecule (torsion angles C(17)-N(4)-C(14)-C(15) and C(18)-N(4)-C(14)-C(13) of −4.3 (7) and −8.5(7)°) (Fig. 2(a)) while II the methyl group of the C 2 H 5 substituent points out of the average molecular mean plane by 1.24 Å (Fig.…”

“…In a previous study carried out on zinc complexes formed by the 5substituted-8-hydroxyquinolines HQ′-AB-C 6 H 4 NMe 2 (AB: NN, CHN and CH 2 -NH 2 ) we observed that the NN-C 6 H 4 NMe 2 group is responsible for low energy bands in the absorption and emission spectra of the metal complex. 3d Moreover, the azo linker is known to be an efficient electronic bridge, which prompts the creation of extended -conjugated systems, 7 therefore, appropriate aromatic azo compounds can be considered as electron transport molecular materials.…”