Charge-Separated Mixed Valency in an Unsymmetrical Acceptor–Donor–Donor Triad Based on Diarylboryl and Triarylamine Units

Abstract

In this study, we report the generation of new mixed-valence (MV) subspecies with charge-separated (CS) characters from an unsymmetrical acceptor−donor−donor (A−D−D) triad. The triad was synthesized by attaching a dimesitylboryl group (A) to a D−D conjugate that consisted of triarylamine (NAr 3 ) units. The MV radical cation, obtained by chemical oxidation of the triad, exhibited a strong intervalence charge transfer (IVCT) absorption derived from the bis(NAr 3 ) •+ moiety in the near-IR region. The chargeseparated MV (CSMV) state, obtained by photoexcitation of the triad, caused a blue shift in IVCT energy in the femtosecond transient absorption spectra, reflecting a bias of positive charge distributions to the D end site. This resulted from increased electron density at the A site and restructuring of the central D site from NAr 3 to NAr 2 sites. Interestingly, any shift in the IVCT energy that was caused by the polarity of the solvent was minimal, reflecting the unique characteristics of the CSMV state. These findings represent the first detailed analysis of the CSMV state, including a comparison with conventional MV states. Therefore, this work provides new insights into counterion-free MV systems and their applications in molecular devices.

Zwitterionic Mixed Valence: Internalizing Counteranions into a Biferrocenium Framework toward Molecular Expression of Half‐Cells in Quantum Cellular Automata

“…The unique characteristics of the counterion-free MV systems are clarified by drawing similarities between 1 and 2 in the ZIMV and CSMV states, respectively.F or both of the MV subspecies, the IVCT energies increasedc ompared to that of the conventional MV species under external stimuli (i.e.,g uest anions for 1 and light for 2 [29] ). This may be attributed to the charge-responsive site (A) increasing DG 0 by perturbing the neighboring redox site.…”

“…In our previous work related to molecular QCA, we realized Lent's proposal of self‐doping of an MV precursor by photoinduced charge separation in an unsymmetrical acceptor–donor–donor (A–D–D) triad (Scheme d) . Through a covalent connection, a dimesitylboryl (BMes 2 ) substituent was attached to a bistriarylamine framework, which is often used for organic precursors of class III MV cations in the Robin–Day classification.…”

“…[28] In our previous work relatedt om olecular QCA, we realized Lent's proposal of self-doping of an MV precursor by photoinduced charge separation in an unsymmetrical acceptordonor-donor (A-D-D) triad (Scheme 1d). [29] Through ac ovalent connection, ad imesitylboryl( BMes 2 )s ubstituent was attached to ab istriarylamine framework, [30,31] which is often used for organic precursors of class III MV cations in the Robin-Day classification. Photoexcitation of the triad 2 led to the chargeseparated MV (CSMV) state (denoted as 2*), the delocalized natureo fw hich was unambiguously characterizedb yf emtosecond transient UV/Vis/NIR spectroscopy.T of urtherd iversify mixed valency in the ground state, we exploited the excellent versatility of the electron-deficient boron center in the BMes 2 group as aL ewis acid, as previously provenf or several A-D conjugates.…”

Small anion-assisted electrochemical potential splitting in a new series of bistriarylamine derivatives: organic mixed valency across a urea bridge and zwitterionization

“…Mixed-valence (MV) compounds have received increasing attention from the viewpoint of fundamental research on intramolecular electron transfer phenomena and application in molecular devices [1–5]. The radical cations of bistriarylamine derivatives bis(NAr 3 ) are well-known MV compounds having π-conjugated bridges (where NAr 3 = triarylamine) [6–18]. These studies focused on evaluating the intervalence charge transfer (IVCT) transition near-infrared (NIR) absorption from NAr 3 to NAr 3 •+ units [1–5].…”

“…The IVCT absorptions of MV compounds are generally more pronounced in organic species [19–20] than in their inorganic counterparts. The strong IVCT characteristics of the bis(NAr 3 ) •+ radical cations are well documented due to their good availability through common N–C bond-forming reactions and the stability of the NAr 3 •+ unit [6–18]. Photoswitchable mixed valency has recently been demonstrated with bis(NAr 3 ) •+ radical cations having dithienylethene bridges [21–22].…”