Tuning the Electronic Coupling and Electron Transfer in Mo₂ Donor–Acceptor Systems by Variation of the Bridge Conformation

Abstract

Assembling two quadruply bonded dimolybdenum units [Mo2 (DAniF)3 ](+) (DAniF=N,N'-di(p-anisyl)formamidinate) with 1,4-naphthalenedicarboxylate and its thiolated derivatives produced three complexes [{Mo2 (DAniF)3 }2 (μ-1,4-O2 CC10 H6 CO2 )], [{Mo2 (DAniF)3 }2 (μ-1,4-OSCC10 H6 COS)], and [{Mo2 (DAniF)3 }2 (μ-1,4-S2 CC10 H6 CS2 )]. In the X-ray structures, the naphthalene bridge deviates from the plane defined by the two Mo-Mo bond vectors with the torsion angle increasing as the chelating atoms of the bridging ligand vary from O to S. The mixed-valent species exhibit intervalence transition absorption bands with high energy and very low intensity. In comparison with the data for the phenylene analogues, the optically determined electronic coupling matrix elements (Hab =258-345 cm(-1) ) are lowered by a factor of two or more, and the electron-transfer rate constants (ket ≈10(11) s(-1) ) are reduced by about one order of magnitude. These results show that, when the electron-transporting ability of the bridge and electron-donating (electron-accepting) ability of the donor (acceptor) are both variable, the former plays a dominant role in controlling the intramolecular electron transfer. DFT calculations revealed that increasing the torsion angle enlarges the HOMO-LUMO energy gap by elevating the (bridging) ligand-based LUMO energy. Therefore, our experimental results and theoretical analyses verify the superexchange mechanism for electronic coupling and electron transfer.

Efficient electron transfer across hydrogen bond interfaces by proton-coupled and -uncoupled pathways

“…3. For both of the systems, the IVCT band parameters, including transition energy ( E IT ), band intensity ( ε IT ), and half bandwidth (Δ ν 1/2 ), are comparable with those found for other Mo 2 dimers with various π bridges differing in length 14,31,32 , symmetry 19 , conjugation 33 , and conformation 34 . As expected, the absorption spectra of the corresponding monomers, [Mo 2 (DArF) 3 (O 2 CCONH 2 )] 0/+ , obtained in DMF do not exhibit the characteristic IVCT transition, as shown in Supplementary Figure 38.…”

Mediation of Electron Transfer by Quadrupolar Interactions: The Constitutional, Electronic, and Energetic Complementarities in Supramolecular Chemistry

“…The larger H ab values for [ thi-(OS) 2 ] + as compared with [ thi-(SS) 2 ] + are in sharp contrast to observations that substitution of S atoms for the O chelating atoms greatly improves the EC between the two bridged Mo 2 centers (Xiao et al., 2013, Tan et al., 2017). Furthermore, in benzene and toluene, these two MV complexes exhibit the IVCT bands much narrower than those in dipole solvents (Table S4) (Wu et al., 2017) and those observed for other weakly coupled {[Mo 2 ]-bridge-[Mo 2 ]} + complexes in DCM (Xiao et al., 2013, Shu et al., 2014, Tan et al., 2017, Kang et al., 2016). This implies that the nature of the bridge is somehow altered, in accordance with the computational results (Figure 4D).…”

“…In the spectra, the MLCT energies ( E ML ) decrease and intensities increase when the chelating atoms change from N to O to S (Table 1), parallel to the phenylene bridged series (Xiao et al., 2013, Liu et al., 2013). Provided with the well-defined MLCT absorptions in the [Mo 2 ]-bridge-[Mo 2 ] systems, together with the bridging ligand to metal charge transfer (LMCT) bands for the MV complexes, we have verified the distant (Zhu et al., 2016), conformational (Kang et al., 2016, Chen et al., 2018), and conjugational (Gao et al., 2019) dependences of the superexchange (McConnell, 1961, Creutz et al., 1994) ET under the semi-classical theoretical framework. For [ thi- ( OS) 2 ] and [ thi- ( SS) 2 ] in the quadrupolar solvents, the MLCT band profiles are apparently changed and the intensity is lowered, in comparison with the spectra in DCM.…”

Biodegradable Gene Carriers Containing Rigid Aromatic Linkage with Enhanced DNA Binding and Cell Uptake

“…Cell Counting Kit-8 (CCK-8) was purchased from Dojindo Laboratories (Kumamoto, Japan). Naphthalene-1, 4-diyldimethanol was prepared according to the literature [36]. All other reagents used in the synthesis, if not specified, were obtained from J&K Scientific Ltd. (Beijing, China) and used without further purification.…”