Luminescent Platinum(II) Terpyridyl‐Capped Carbon‐Rich Molecular Rods—An Extension from Molecular‐ to Nanometer‐Scale Dimensions

Abstract

There has been a growing interest in the chemistry of carbonrich metal-containing systems, in particular those of metalcontaining polyynes. Examples include the transition-metal [1] trans-[Pt(C 6 F 5 )(PR 3 ) 2 ], [2] Fe(Cp*)(dppe), [3] Fe(Cp*)(CO) 2 , [4] Ru(Cp)(PPh 3 ) 2 , [5] Mn(dppe) 2 I, [6] Re(tBu 2bpy)(CO) 3 , [7] Au(PCy 3 ) [8] ). Some of them have recently been shown to display interesting luminescence behavior. [7,8] Despite platinum-containing polyynes being known, most of them are confined to platinum phosphane complexes, with corresponding studies on the nitrogen donor analogues unexplored. These, together with the numerous studies on the luminescence behavior of platinum(ii)-polypyridine systems, [9,10] in particular those of the platinum(ii)-terpyridyl complexes, [9f, 10] and our recent report on the novel solvatochromic properties of platinum(ii)-terpyridyl complexes [11] as well as our interest in luminescent carbon-rich molecular materials, [12] have prompted us to investigate the luminescence properties of the [Pt]-(C C) n -[Pt] system of various alkynyl chain lengths with platinum(ii)-terpyridyl groups as the transition-metal end-capped termini. Herein we report the synthesis, electronic absorption, photophysical properties, and structural characterization of a series of alkynyl-bridged dinuclear platinum(ii)-terpyridyl complexes, [Pt(tBu 3 -tpy)-(CC) n Pt(tBu 3 -tpy)](X) 2 (1-3; tBu 3 -tpy = 4,4',4''-tri-tertbutyl-2,2':6',2''-terpyridine). The bulky trisubstituted terpyridine ligand was chosen to eliminate the influence of Pt···Pt and p-p interactions on the luminescence behavior. The luminescence behavior together with the structure-property relationship of the complexes have been studied. Figure 1 depicts the structures of the complex cations of 1-3. In all cases, the platinum(ii) metal center adopts an

Single-stranded nucleic acid-induced helical self-assembly of alkynylplatinum(II) terpyridyl complexes

“…(Higher oligomers could not be observed in the ESI-MS experiments because their m/z values are beyond the detection range of our instrument.) In addition, a very weak emission band at Ϸ800 nm also starts to appear at Ϸ15 M complex concentration, and its intensity becomes stronger with increasing complex concentrations, probably ascribed to an excited state of a triplet metal-metal-to-ligand charge transfer ( 3 MMLCT) origin based on previous studies on related systems (17)(18)(19)(20)(21). Nevertheless, at a 30 M complex concentration, which is used throughout the current investigation, the 800 nm background emission bands are very weak and just barely recognizable for both complexes.…”

“…On the basis of our previous work (17)(18)(19)(20)(21) and other related studies (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16), the newly formed UV-vis bands of complexes 1 and 2 at longer wavelength are assigned as MMLCT transitions, as a result of the self-assembly of the complexes induced by the oligonucleotides through metal⅐⅐⅐metal and ⅐⅐⅐ interactions. The newly formed emission bands are attributed to MMLCT triplet emission.…”

“…Because poly(dT) 25 and poly(dA) 25 carry the same number of negative charges, there is no obvious reason to assume that the positively charged complex cations would interact electrostatically with poly(dA) 25 in a much weaker fashion than that with poly(dT) 25 . The very broad emission is likely to be a mixture of MMLCT triplet emission which is a result of complex aggregation (at Ϸ800 nm) and complex monomer emission (17)(18)(19)(20)(21). Because poly(dA) has been shown to assume a helical structure (right-handed) stabilized through adenine base stacking interactions (25,28,29), it is likely that the hydrophobic interactions between the relatively hydrophobic planar adenine base and the square-planar platinum complex cations would reduce the tendency for the complex cations to stack with each other to form a helical self-assembly, resulting in the reduced chirality induced and the observation of emission from the mononuclear platinum species.…”

“…Recently, we have synthesized a number of platinum(II) polypyridyl alkynyl complexes that show interesting spectroscopic and luminescence properties (17)(18)(19)(20)(21). One particularly interesting observation is that solvents of different polarity and also polyacrylate could induce the aggregation of the positively charged platinum complexes in organic solvent mixtures (19,21).…”

Crystal structure of diiodo-(4′-(2-pyridyl)-2,2′:6′,2″-terpyridine)cadmium(II), Cd(C20H14N4)I2

“…The Cd(II) is fivecoordinate with the expected pattern of longer Cd-Nbonds to the terminal rings of 2-pytpy (d(Cd-N1) =2.369 (4), d(Cd-N3) =2.370(4) Å)than to the central ring (d(Cd-N2) =2.311(4) Å). The coordination of the metal is best described as as quare pyramid in which the axial site is occupied by I2 and the squarebase by N1, N2, N3 and I1.…”