NOVELTY - Compound (I) comprising a redox auxiliary moiety and a reactive moiety is new. The redox auxiliary moiety is bonded to the reactive moiety. The oxidation of the redox auxiliary activates the reactive moiety and catalyzes the conversion of the reactive moiety to a product. The redox auxiliary moiety can undergo reversible oxidation. Provided that if the reactive moiety is norbornadiene, the redox auxiliary moiety is neither N,N-bis(4- methoxyphenyl)aniline nor N-phenyl-N,N,N-tris(4-methoxyphenyl)benzene-1,4-diamine.    USE - (I) is useful: for a chemical reaction useful to store solar energy, and/or as a mechanical switch (all claimed); and as a solar fuel.    ADVANTAGE - (I): utilizes arylamine which has a high degree of thermal stability; exhibits high reactivity; and provides solar fuels which are alternative source of energy for replacing fossil fuels especially where storage is essential.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) substituted diphenyldiazene compounds of formula (II); and    (2) activating a compound for a chemical reaction, comprising functionalizing a compound with a redox auxiliary group, and oxidizing the redox auxiliary moiety that is bonded to the compound, thus activating the compound, where the activated compound undergoes a chemical reaction to form a product, and the oxidation of the redox auxiliary moiety is reversible.    A1-A4 = H, halo or any other sterically allowable group;    B1-B3 = 1-24C alkyl, 2-24C alkenyl, 2-24C alkynyl, aryl, heteroaryl (all optionally substituted), H, halo, alkoxy, OH, nitrile, nitro, -C(O)R11, -NR11R12 or -C(O)NR11R12;    D1-D3 = 1-24C alkyl, 2-24C alkenyl, 2-24C alkynyl, aryl, heteroaryl (all optionally substituted), H, halo, alkoxy, OH, nitrile, nitro, -C(O)R11, -NR11R12 or -C(O)NR11R12; and    R11, R12 = 1-24C alkyl, 2-24C alkenyl, 2-24C alkynyl, aryl, heteroaryl (all optionally substituted), H or halo.    Provided that at least one of D1-D3 is a redox auxiliary moiety that can undergo reversible oxidation.