Tetraaminoperylenes: their efficient synthesis and physical properties.

Abstract

Trimethylsilylation of 1,8-diaminonaphthalene gave 1,8-bis(trimethylsilylamino)naphthalene (1 a), which was in turn lithiated with two molar equivalents of n-butyllithium to give the tris(thf)-solvated dilithium diamide [1,8-[(Me(3)SiN)Li(thf)](2)C(10)H(6)](thf) (2 a). Metal exchange of 2 a with TlCl was carried out in two steps, via the previously characterized mixed-metal amide [1-[(Me(3)SiN)Li(thf)(2)]-8-[(Me(3)SiN)Tl]C(10)H(6)], to give the dithallium diamide [1,8-[(Me(3)SiN)Tl](2)C(10)H(6)] (3 a). Thermolysis of 3 a cleanly gave a 1:1 mixture of the 4,9-bis(trimethylsilylamino)perylenequinone-3,10-bis(trimethylsilylimine) (4 a) and 1 a. By this route, a whole series of silylated homologues of 4 a was obtained in good yields, while the same method proved to be inefficient for the synthesis of the alkyl-substituted analogues. Compound 4 a and its tert-butyldimethylsilyl derivative 4 d were reduced with sodium amalgam to give, after protonation, the corresponding 3,4,9,10-tetraaminoperylenes 7 a and 7 d. Cyclic voltammetry showed two reversible, closely spaced reduction waves (E(red 1)=-1.39, E(red 2)=-1.59 V versus SCE) corresponding to this conversion. The perylenes 7 a and 7 d are thought to be the primary products in the reaction cascade leading to the perylene derivatives, involving the thermal demetalation of the thallium amides, possibly via Tl(II)bond;Tl(II) intermediates, first to give 7 a and its analogues. The final oxidation of the tetraaminoperylenes by one molar equivalent of 3 a and analogous thallium amides gave the quinoidal derivatives such as 4 a and 4 d, a step that could be studied by direct reaction of the isolated species. The UV/Vis absorption spectra of the 4,9-bis(silylamino)perylenequinone-3,10-bis(silylimines) are characterized by a long-wavelength absorption band with a pronounced vibrational structure (lambda(max)=639 nm, lg epsilon =4.53) attributed to a pi*<--pi and a pi*<--n absorption band at 454 nm (lg epsilon 4.83), along with intense absorption in the UV region. A weak red emission with a rather low quantum yield (Phi(fl)=0.001, lambda(max)=660 nm) is observed upon irradiation of a sample; the lifetime of the emission is only 66 ps. The low emission quantum yield is attributed to the *pi<--n transition of the amino perylene, which induces strong spin-orbit coupling, leading to a large triplet yield. The triplet state was probed by transient absorption spectroscopy and found to have a lifetime of 200 ns in air, and 1100 ns in argon-flushed solution. Treatment of 4 a with a stoichiometric amount of KF in methanol/water under phase-transfer conditions (with the cryptand [C 222]) gave an almost quantitative yield of the parent compound 4,9-diaminoperylenequinone-3,10-diimine (8). Treatment of 8 with two molar equivalents of the ruthenium complex [Ru(bpy)(2)(acetone)(2)](PF(6))(2), generated in situ, yielded the blue dinuclear ruthenium complex [(bpy)(4)Ru(2)[mu(2)-N,N':N",N"'-[[4,9-(NH(2))(2)-3,10-(NH)(2)]C(20)H(8)]]](PF(6))(4) (9), the redox properties of which were studied by cyclic voltammetry. The difference in the potentials of the two one-electron redox steps (225 mV) indicates strong coupling of the metal centers through the 4,9-diaminoperylenquinone-3,10-dimine bridging ligand and corresponds to a comproportionation constant K(c) of 6.3 x 10(3). The UV/Vis absorption spectrum of the mixed valent form, which is stable in air, has a characteristic intervalence charge-transfer (IVCT) band in the near infrared at 930 nm (lg epsilon =3.95), from which an electronic coupling parameter J of 760 cm(-1) could be estimated, placing compound 9 at the borderline between the class II and class III cases in the Robin-Day classification.