Spectroscopic and Luminescence Studies on Square-Planar Platinum(II) Complexes with Anionic Tridentate 3-Bis(2-pyridylimino)isoindoline Derivatives

Abstract

Reactions of 1,3-bis(2-pyridylimino)isoindoline (HL1), 1,3-bis(2-pyridylimino)benz(f)isoindoline (HL2), or 5,6-dihydro-2,3-diphenyl-5-(pyridin-2-ylimino)pyrrolo[3,4-b]pyrazin-7-ylidene)pyridin-2-amine (HL3) with Pt(tht)(2)Cl(2) (tht = tetrahydrothiophene) afforded the corresponding Pt(L)Cl complexes. A series of neutral platinum(II) alkynyl complexes Pt(L)(C[triple bond]CR) were prepared by reactions of the precursors Pt(L)Cl with alkynyl ligands through CuI-catalyzed platinum acetylide sigma coordination. Crystal structural determination of Pt(L3)Cl (3), Pt(L1)(C[triple bond]CPh) (4), and Pt(L1)(C[triple bond]CC(6)H(4)Bu(t)-4) (6) by X-ray crystallography revealed that the neutral platinum(Pi) complexes with monoanionic tridentate L ligands display more perfect square-planar geometry than that in platinum(II) complexes with neutral tridentate 2,2':6',2''-terpyridyl ligands. Both the Pt(L)Cl and Pt(L)(C[triple bond]CC(6)H(4)R-4) complexes exhibit low-energy absorption at 400-550 nm, arising primarily from pi --> pi*(L) intraligand (IL) and 5d(Pt) --> pi*(L) metal-to-ligand charge-transfer (MLCT) transitions as suggested from density functional theory calculations. They display bright-orange to red room-temperature luminescence in fluid dichloromethane solutions with microsecond to submicrosecond ranges of emissive lifetimes and 0.03-3.79% quantum yields, originating mainly from (3)IL and (3)MLCT excited states. Compared with the emissive state in Pt(L)Cl complexes, substitution of the coordinated Cl with C[triple bond]CC(6)H(4)R-4 in Pt(L)(C[triple bond]CC(6)H(4)R-4) complexes induces an obviously enhanced contribution from the (3)[pi(C[triple bond]CC(6)H(4)R-4) --> pi*(L)] ligand-to-ligand charge-transfer (LLCT) triplet state. The photophysical properties can be finely tuned by modifying both the L and alkynyl ligands. The calculated absorption and emission spectra in dichloromethane coincide well with those measured in a fluid dichloromethane solution at ambient temperature.

Phosphorescent Square‐Planar Platinum(II) Complexes of 1,3‐Bis(2‐pyridylimino)isoindoline with a Monodentate Strong‐Field Ligand

“…Selected bond lengths and angles are listed in Table 1 and an ORTEP diagram is depicted in Figure 1. The platinum(II) center is located in an approximately square‐planar environment with adjacent angles being 88.9(4)–90.9(5)° and opposite angles being 177.3(12) and 178.9(3)°, affording a geometry that is more perfectly square‐planar geometry than those of other tridentate cyclometalated platinum(II) complexes38,52,53 or BPI platinum(II) complexes with ethynylaryl or pyridyl as auxiliary ligands 27,28. This is because the two six‐membered chelating rings formed by chelating ligand BPI and the Pt atom exhibit less steric constraint than those in platinum(II) complexes bearing terpyridine ligands with two five‐membered chelating rings 54–57.…”

“…This is because the two six‐membered chelating rings formed by chelating ligand BPI and the Pt atom exhibit less steric constraint than those in platinum(II) complexes bearing terpyridine ligands with two five‐membered chelating rings 54–57. At the same time, the CN ligand imposes less steric hindrance than ethynylaryl and pyridyl ligands 27,28. The Pt–N3 [2.007(10) Å] distance is shorter than that in [Pt(BPI)(Ph‐4‐NMe 2 )] (2.038 Å),29 but longer than those (1.96–1.99 Å) in [Pt(BPI)X] (X = Cl, ethynylaryl, and pyridyl)27,28 derivatives due to the weaker trans effect of cyanide compared with the p ‐dimethylaminophenyl group but stronger effect than shown by other ligands.…”

“…[27–29,32] It has been demonstrated that the absorption and luminescence properties can be modulated by substitution of the coordinated chloride in [Pt(BPI)Cl] with a monodentate ligand or by modification of BPI by introducing electron‐donating or ‐withdrawing substituents as well as changing the π‐conjugated systems. [27–29,32] The platinum(II) complexes with an acetylide as a co‐ligand display long‐lived luminescence due to the fact that the strong‐field alkynyl ligand induces the d–d state, which has relatively inaccessible energies, and consequently suppresses nonradiative deactivation of the d–d state 28. These compounds give rise to intense and long‐lived luminescence originating from intraligand (IL), metal‐to‐ligand charge transfer (MLCT), and ligand‐to‐ligand charge transfer (LLCT) transitions 28.…”

“…[27–29,32] The platinum(II) complexes with an acetylide as a co‐ligand display long‐lived luminescence due to the fact that the strong‐field alkynyl ligand induces the d–d state, which has relatively inaccessible energies, and consequently suppresses nonradiative deactivation of the d–d state 28. These compounds give rise to intense and long‐lived luminescence originating from intraligand (IL), metal‐to‐ligand charge transfer (MLCT), and ligand‐to‐ligand charge transfer (LLCT) transitions 28. Substitution of the coordinated chloride by a neutral N‐heterocyclic ligand induces a distinct blueshift for both low‐energy absorption and emission bands due to an enhanced 3 IL state and reduced 3 MLCT character, as demonstrated experimentally and theoretically 27…”

Synthesis and characterization of membrane stable bis(arylimino)isoindole dyes and their potential application in nano-biotechnology

“…24 Platinum coupled 1,3-bis(imino)isoindole derivatives exhibit great photophysical and photoemission properties. 25 In the present work, the design of the dyes utilized a 1,3-bis(aryl imino)isoindole (aryl: compound 1 = 2-aminopyridine; compound 3 = 4-butyl aniline) moiety and a strategically placed acyl fatty acid chain (R= −C 8 H 17 ) to provide membrane stability (Figure 1; compounds 1, 3 ). The aryl amines were selected based on their potential ability to form intra molecular hydrogen bonds within the molecule itself.…”