Synthesis, spectroscopic and electrochemical investigations of supramolecular nickel(II)tetraazaporphyrin complexes

Abstract

The (bpy) 2 Ru II and (phen) 2 Ru II moieties were linked to [Ni(OBTTAP)] 1, periphery through coordinate bonds in order to synthesize cationic di-and pentanuclear complexes 2-5 that were obtained as PF 6 -salts. They were characterized by IR, 1 H NMR, UV-vis, and mass spectral data. The electronic absorption, emission and redox data of these bichromophoric systems indicate the presence of a high degree of intercomponent electronic interaction. The position and relative intensities of the Soret and Q bands in these complexes is altered due to peripheral binding of the metal units. The compounds were non-emissive for the Q band excitation but, Soret excitation led to a strong S 2 emission, observed between 400-450 nm. In cyclic voltammetry, the compounds exhibited one Ru centered oxidation together with one or two OBTTAP centered oxidations. The Ru II /Ru III oxidations were observed at significantly lower potentials as compared to the corresponding simple maleonitrilebenzylthioether complexes and has been interpretted in terms of weaker dπ(S)−dπ(Ru) interactions.

Stepwise synthesis of peripherally dimetallated metallo-tetraazaporphyrins with linear and bent motifs

“…But unlike, the di-and trinuclear complexes (2)-(5) exhibited two reversible oxidation waves, one at significantly less positive potential between E 1/2 0.45-0.60 V and the second between E 1/2 0.99-1.13 V, besides an irreversible oxidation between E p,a =1.28-1.45 V ( Figure 6). Since the low potential reversible oxidation waves are the characteristic of the oxidation of (bpy) 2 Ru II moiety linked to weak p-acid ligands, the first low potential reversible oxidation wave in each complex (2)-(5) could be attributed to Ru II / Ru III oxidation of the peripheral units in conformity with the literature data [13][14][15][16]. The second and third oxidation waves that are observed at potentials closer to the OMTTAP/OMTTAP 2+ oxidation of the precursor complex (1) could be assigned to the first and the second oxidation of the OMTTAP unit.…”

“…These hybrid systems are specifically suitable because of their characteristic photophysical properties such as long lived MLCT excited states, intense absorption in the visible region and redox stability of the individual molecular units [11,12]. Over the past few years we have been engaged in synthesis and study of metallo-tetraazaporphyrin/ polypyridylruthenium(II) linked molecular arrays [13][14][15][16]. We have also fabricated metallo-tetraazaporphyrin based potentiometric sensors for a few cations and anions [17][18][19][20].…”