Charge Transfer Switching in Donor–Acceptor Systems Based on BN-Fused Naphthalimides

Abstract

Six-membered azaborine rings have been straightforwardly fused on naphthalimide-based donor-acceptor systems, and a series of BN-containing heteroaromatic compounds BN1-BN3 were constructed. Electron-donating triphenylamines were functionalized in the extended direction of the 3- or/and 4-position of the naphthalimide unit. For comparison, reference BN0 without triphenylamine was also prepared. The intramolecular charge transfer (ICT) interactions in the resulting BN-fused naphthalimides (BN0-BN3) together with their precursors (N0-N3) and fluoride-coordinated analogues (FBN0-FBN3) have been systematically investigated by photophysical, electrochemical, and theoretical approaches. It is found that the fusion of the azaborine ring has a great effect on the ICT properties of the D-A systems based on BN-fused naphthalimides. For the precursors without boron, the extension of an electron donor from the 3-position of naphthalimide is superior in enhancing the D-A interactions. On the contrary, upon fusion of the azaborine ring on naphthalimide, the dominant orientation of the ICT interactions conversely converts to the extended direction of the 4-position of naphthalimide in the D-A molecules based on BN-fused naphthalimides. Most interestingly, upon coordinating the boron by a fluoride ion, the ICT interactions are dramatically enlarged and the substitution position of the triphenylamino group has a negligible effect on the ICT properties of the fluoride-coordinated analogues.

BN‐Embedded Polycyclic Aromatic Hydrocarbon Oligomers: Synthesis, Aromaticity, and Reactivity

“…As shown in Figure , the LUMO of BN1 delocalizes over the whole aromatic skeleton, while the HOMO has no weight at the boron atom. Unlike previously reported heteroatom‐substituted PAHs containing separated boron and nitrogen where the charge can facilely transfer from the nitrogen center to the boron center, only slight charge separation can be found in BN1, which results in the weak charge transfer interactions in azaborine containing compounds . Similarly, with the BN‐conjugation extension, oligomers BN2, BN3, and BN4 demonstrate delocalized HOMOs but without any distribution on the boron atoms.…”

“…Unlike previously reported heteroatomsubstituted PA Hs containing separated boron and nitrogen where the charge can facilely transfer from the nitrogen center to the boron center, [28] only slight charge separation can be found in BN1, which results in the weak charge transfer interactions in azaborine containing compounds. [29] Similarly,with the BN-conjugation extension, oligomers BN2, BN3, and BN4 demonstrate delocalized HOMOs but without any distribution on the boron atoms.Moreover,both HOMOs and LUMOs of oligomers BN2, BN3, and BN4 are partially delocalized over the inner aromatic rings with ignorable weights on the two terminal sides.T hese results suggest that the inner aromatic moieties are more reactive than the two terminal parts.M ost interestingly,o ligomers BN2, BN3, and BN4 display nodal-shaped HOMOs with boundaries at the BN units.T his suggests that the conjugation extension in the vertical backbone is more pronounced on the effective conjugation length than the other horizontal one.T he calculated energies,o scillator strength, and compositions of major electronic transitions are shown in the Supporting Information, Tables S5-S8 and the calculated HOMO-LU-MO levels for the oligomers are consistent with those experimentally determined values.…”

UV-irradiation of self-assembled triphenylamines affords persistent and regenerable radicals

“…Although ICT typically requires a donor–π–acceptor system,26 the TPA units of 2 and 3 could rotate over to each other allowing the TPA units on either side of the urea tether to act as both the donor and acceptor in the ICT exchange without the need for a π-system intermediate. For this case, the TPAs would have to adopt acceptor characteristics since TPAs are typically only the donor in ICT systems 27. As seen in Fig.…”

B2N2‐Embedded Polycyclic Aromatic Hydrocarbons with Furan and Thiophene Derivatives Functionalized in Crossed Directions

“…However, due to the corrosive characteristic of BBr 3 on the electrodes, the CV measurements on the complexes between the B 2 N 2 ‐embedded PAHs and BBr 3 were not carried out. Interestingly, upon coordination of excess fluoride ions, all the fluoride coordinated compounds exhibited two reversible or quasi‐reversible couples (Figure b) at relatively low potentials, corresponding to the sequential removal of electrons at the two four‐coordinate boron centers . This also suggests that the two boron atoms in the B 2 N 2 ‐embedded PAHs are both coordinated with the fluoride ions and converted into strong electron donors.…”

“…Interestingly,u pon coordination of excess fluoride ions, all the fluoride coordinated compounds exhibited two reversible or quasi-reversible couples (Figure 9b)a tr elatively low potentials, correspondingt ot he sequential removal of electrons at the two four-coordinate boron centers. [33] This also suggests that the two boron atoms in the B 2 N 2 -embedded PAHs are both coordinated with the fluoride ions and converted into strong electron donors. As showni nF igure 9b,t wo fluorides coordinated dianion 2F-BNFS 2À À displays two redox couples at half-wave potentials of À0.43 and À0.08 V, respectively.T he splitting of 0.35 Vi mplies that the two fluoridec oordinated boronm oieties cannotb e oxidizeda ti dentical potential and ah igher potentiali sn eeded to transform 2F-BNFS À À C into 2F-BNFS.S imilar oxidation separations can be also observed for other fluoride coordinated analogues, which suggests the charged elocalization on the B 2 N 2embedded PAHs and electron couplings between the two boron centerst hrough the B 2 N 2 -embedded molecular backbones.…”