Ah exaradicaloid molecule with alternating KekulØ and non-KekulØ connectivities between adjacent spin centers was obtained by fusing two conjugation motifs in Chichibabin and Schlenk hydrocarbons into acoronoid structure. 1 HNMR, ESR, and SQUIDe xperiments and computational analyses show that the system has asinglet ground state with asignificant hexaradicaloid character (g 0 = 0.826, g 1 = g 2 = 0.773). It has multiple thermally accessible high-spin states (up to the septet), with uniform energy gaps of ca 1.0 kcal mol À1 between consecutive multiplicities.I nl ine with its open-shell character, the coronoid has as mall electronic band gap (ca. 0.8 eV) and undergoes two consecutive one-electron oxidations at low potentials,yielding cationic forms with extended near-infrared absorption. The hexaradicaloid, whichc ombines open-shell and macrocyclic contributions to its p conjugation, is an example of ad esign strategy for multistate spin switches and redox-amphoteric NIR dyes.

A hexaradicaloid molecule with alternating Kekulé and non‐Kekulé connectivities between adjacent spin centers was obtained by fusing two conjugation motifs in Chichibabin and Schlenk hydrocarbons into a coronoid structure. 1H NMR, ESR, and SQUID experiments and computational analyses show that the system has a singlet ground state with a significant hexaradicaloid character (γ0=0.826, γ1=γ2=0.773). It has multiple thermally accessible high‐spin states (up to the septet), with uniform energy gaps of ca 1.0 kcal mol−1 between consecutive multiplicities. In line with its open‐shell character, the coronoid has a small electronic band gap (ca. 0.8 eV) and undergoes two consecutive one‐electron oxidations at low potentials, yielding cationic forms with extended near‐infrared absorption. The hexaradicaloid, which combines open‐shell and macrocyclic contributions to its π conjugation, is an example of a design strategy for multistate spin switches and redox‐amphoteric NIR dyes.

Dedicated to Prof. Klaus Müllen on the occasion of his 75th birthdayA family of tunable halochromic switches is developed using a naphthalimide-fused dipyrrin as the core 𝝅-conjugated motif. Electronic properties of these dipyrrins are tuned by substitution of their alpha and meso positions with aryl groups of variable donor-acceptor strength. The first protonation results in a conformational change that enhances electronic coupling between the dipyrrin chromophore and the meso substituent, leading to halochromic effects that occasionally exceed 200 nm and switch the absorption between the near-infrared (NIR)-I and NIR-II ranges. A NIR-II photothermal effect, switchable by acid-base chemistry is demonstrated for selected dipyrrins. Further protonation is possible for derivatives bearing additional amino groups, leading to up to four halochromic switching step. The most electron-rich dipyrrins are also susceptible to chemical oxidation, yielding NIR-absorbing radical cations and closed-shell dications.

A typical π bond is weakened by oxidation and reduction, corresponding respectively to the removal of electrons from bonding orbitals and addition of electrons to antibonding orbitals, and by unpairing of the bonding electrons, e.g. in the triplet state. Here we describe tetrafluorenofulvalene (TFF), a twisted, open-shell alkene for which these general rules no longer hold. In particular, the bond in TFF becomes significantly stronger in the tri- and tetraanion, which can be generated by chemical reduction. While the triplet state of TFF does contain a weaker alkene bond than the singlet, in the quintet state the bond order increases significantly, yielding a flatter structure. The behavior of TFF originates from the doubly bifurcated topology of the underlying spin system and can be rationalized by the balancing effects of benzenoid aromaticity and spin paring.