Structure, optical and magnetic properties of radical anion, dianion salts and coordination complexes of organic dye 3,4:9,10-perylenetetracarboxylic dianhydride (PTCDA)

Abstract

Reduction of organic dye 3,4:9,10-perylenetetracarboxylic dianhydride (PTCDA) yields a series of radical anion and dianion salts of PTCDA (1–5). Their formation is accompanied by essential red shift and splitting of absorption bands of pristine PTCDA (493 and 560 nm) which appear nearly in the whole visible range, namely, at 660, 700 and 760–770 nm for the radical anions, and 514–526, 544–569, 633–644 and 700–713 nm for the dianions. Weaker bands are also observed in the NIR range at 954 and 938–940 nm, respectively. Reduction elongates double CO bonds, and the shape of the anions becomes non-planar due to twisting. A dihedral angle between two planar halves of PTCDA increases together with anion charge. The PTCDA•− radical anions form {PTCDA}22− dimers in 1–3 with short interplanar distances of 3.220–3.299 Å. These dimers show intense charge transfer bands at 1460–1480 nm and they are diamagnetic up to 360 K indicating large singlet-triplet energy gap for them. The dianions are diamagnetic in the salts. The PTCDA2− dianion can also form coordination complexes coordinating two potassium cations in {cryptand(K+)}2(PTCDA2−)⋅C6H4Cl2 (6) or vanadocene cation in {cryptand(K+)}(Cp2V+)(PTCDA2−)⋅C6H4Cl2 (7). Mixed {cryptand(K+)}2(PTCDA2−){GaIIICl(Pc•3−)}•−⋅2C6H4Cl2 (Pc: phthalocyanine, 8) salt containing two strongly absorbing anionic chromophores has also been obtained. Both anions are chequered in the layers forming short CO(PTCDA2−)⋅⋅⋅H[GaIIICl(Pc•3−)}•−] hydrogen bonds. Most probably, namely these bonds provide rather effective antiferromagnetic coupling of the [GaIIICl(Pc•3−)}•−] spins (S = 1/2) within the layers with large negative Weiss temperature of −25 K.