Solid‐State Phosphorescence of trans‐Bis(salicylaldiminato)platinum(II) Complexes Bearing Long Alkyl Chains: Morphology Control towards Intense Emission

Abstract

Morphology control for intense solid-state phosphorescence of non-emissive, but potentially emissive crystals of platinum complexes and the mechanistic rationale are described. A series of trans-bis(salicylaldiminato)platinum(II) complexes bearing linear alkyl chains (1a: n=5; 1b: n=8; 1c: n=12; 1d: n=14; 1e: n=16; 1f: n=18) was synthesized and the solid-state emission properties were examined by using crystals/aggregates prepared under various precipitation conditions. Crystals of 1e, prepared using "kinetic" conditions including rapid cooling, high concentrations, and poor solvents, emit intensive yellow phosphorescence (λ(max)=545 nm) under UV irradiation at 298 K with an absolute quantum efficiency of 0.36, whereas all the crystals of 1a-1f prepared using "thermodynamic" conditions including slow cooling, low concentrations, and good solvents were either non- or less emissive with Φ(298K) values of 0.12 (1a), 0.11 (1b), 0.10 (1c), 0.07 (1d), 0.02 (1e), and 0.02 (1f) under the same measurement conditions. The amorphous solid 1e, prepared by rapid cooling and freeze-drying, was also non-emissive (Φ(298K)=0.02, 0.02). Temperature-dependent emission spectra showed that the kinetic crystals of 1e exhibit high heat-resistance towards emission decay with increasing temperature, whereas the amorphous solid 1e is entirely heat-quenchable. This is a rare example of the change from a non-emissive crystal into a highly emissive crystal by morphology control through crystal engineering. Emission spectra and powder X-ray diffraction (XRD) patterns of the emissive, kinetic crystals of 1e are clearly distinct from those of the less emissive, thermodynamic crystals of 1a-1f. Single-crystal XRD unequivocally establishes that the thermodynamic crystals of 1d have a multilayered lamellar structure supported by highly regulated, consecutive π-stacking interactions between imine moieties, whereas the kinetic crystals of 1e have a face-to-edge lamellar structure with less stacking. These results lead to the conclusion that 1) morphology control of long-chained complexes exclusively generates a metastable herringbone-based lamellar packing motif that exhibits intense emission and high heat-resistance, while 2) a thermodynamically stable, highly regulated, consecutive stacking motif is unfavorable for solid-state emission.

Synthesis, characterization, and anticancer properties of organometallic Schiff base platinum complexes

“…The platinum satellites for the imine resonances (JHPt ~ 62 Hz) are consistent with other (salicylaldiminato)platinum complexes [18][19][20][21][22][23][24][25][26]. The FT-IR spectra show the expected decrease in the frequency of the C=N bond due to complexation, which is observed as the νC=N stretch shifts from ca.1632 cm -1 for the free ligands to ca.…”

Reversible Binding of Solvent to Naked PbII Centers in Unusual Homoleptic Alkynyl‐Based Pt2Pb2 Clusters

“…As an illustration, two views of the extended packing of the solvate 1(acetone) 2 ·2(Me 2 CO) are also shown in Figure 3 c,d, indicating that the acetone molecules are located along these channels. It is worth noting that the incorporation of the solvent increases the separation between clusters of neighboring sheets (4.621-4.939 in 1(acetone) 2 vs. 3.341 in 1), giving rise to a less tightly packed arrangement, which has a positive influence on the emission efficiency, [25] as mentioned below. As in the p-methoxyphenyl derivative 3, in this solvate, each Pb II center is involved in a weak bonding contact with only one acetone (Pb···O1 = 2.918 (5) ); the second acetone acts as the crystallization solvent.…”

Synthesis and Crystal Packing of trans‐Bis(2‐aminotroponato)palladium(II) Complexes Bearing Linear Alkyl Chains – Hard Lamellar Structures Self‐Locked by Cross‐Shaped Molecular Units

“…This characteristic molecular shape generates a moderate balance of molecular mobility and rigidity in the interactions between alkyl chains, is laminated alternately on the c axis with an orthogonal lamellar array of the identical unit. [13] This result indicates that an understanding of the correlation between lamellar structures and the shape of molecular units can aid in the design of future photoelectric devices. A linear correlation between the d-spacing and chain lengths in these compounds indicates that they form the same type of three-dimensional layer-by-layer structure of lamellar aggregates.…”

“…[16] Complexes 1a-1e were characterized using 1 H NMR, 13 C NMR (Figures S1-S5, Supporting Information), and FTIR spectroscopy, and high-resolution mass spectrometry. The 2-(alkylamino)tropones were prepared by reaction of tropolone with SOCl 2 and subsequent amination of the resulting chloride.…”