Nature of the strong electron donor 1,3,6,8-tetrakis(dimethylamino)pyrene and ionicity of its charge transfer complexes

The 1,3,6,8-tetrakis(dimethylamino)pyrene (TDAP) molecule is a stronger ele ctron donor (D) than conventional donor molecules such as tetramethyltetrat hiafulvalene, N,N,N',N'-tetramethyl-p-phenylenediamine and N,N-dimethyldihy drophenazine judged from both their charge transfer (CT) bands with s-trini trobenzene (TNB) complexes and their redox potentials. The first averaged p otential of oxidation and reduction peak potentials of TDAP is +0.02 V vs. SCE in acetonitrile. The molecule easily releases four electrons by two suc cessive redox processes with two-electron transfer at each step as previous ly reported. Semiempirical calculation of molecular conformation infers tha t the peculiar redox behavior may be ascribed to the deformed conformations of cationic species of the TDAP molecule. Complex formation with a variety of acceptor molecules (A): TCNQs, p-benzoquinones and others was examined. With TCNQ derivatives, only tetrafluoro-TCNQ affords a 1 : 1 stoichiometry with an ionic ground state (D2+)(A(2-)). The major ratio of the other CT c omplexes is 1 : 2, those with a strong acceptor in the TCNQ system have a c ompletely ionic ground state; (D2+)(A(-))(2) while those with a weak accept or have a partial CT with the charge of TDAP between +1 and +2; (D)(+2(1-de lta))(A(-(1-delta)))(2) (delta similar to0). A very weak acceptor in the TC NQ system mainly affords the 1 : 3 complex with a partial CT state. In addi tion, the non-substituted TCNQ molecule affords a 1 : 4 complex with a part ial CT state where the cationic species are deduced to be a mixture of TDAP (2+) and protonated TDAP. These partial CT compounds of TCNQs are highly co nductive. The 1 : n (n = 2, 3, 4) complexes are found to contain anion spec ies of TCNQs(-(1-delta)) (delta similar to0) or a mixture of charge separat ed species (A(-gamma) + A(-(1-delta)) or A(-(1-delta)) + A(-2(1-gamma)): ga mma, delta similar to0). A very weak acceptor such as C-60 or TNB affords a neutral complex. On the basis of the ionicity of TDAP CT complexes with TC NQs, p-benzoquinones and others, the criterion for partial CT is discussed.