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Chem Asian J ; 15(3): 406-414, 2020 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-31922659


Molecular functions depend on conformations and motions of the corresponding molecular species. An air-water interface is a suitable asymmetric field for the control of molecular conformations and motions under a small applied force. In this work, double-paddled binuclear PtII complexes containing pyrazole rings linked by alkyl spacers were synthesized and their orientations and emission properties dynamically manipulated at the air-water interface. The complexes emerge from water with concurrent variation of interface orientation of the planes of the PtII complexes from perpendicular to parallel during mechanical compression suggesting a unique 'submarine emission'. Phosphorescence of the complexes is quenched at the air-water interface prior to monolayer formation with intensities subsequently rapidly increasing during monolayer compression. These results indicate that asymmetric reactions and motions might be controlled by applying mechanical force at the air-water interface.

Inorg Chem ; 58(14): 9076-9084, 2019 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-31247829


In this paper, we describe the first phosphorescent molecules that do not exhibit the concentration quenching in the homogeneous solution state throughout the entire range of concentrations. A series of newly designed polymethylene-vaulted trans-bis[2-(iminomethyl)imidazolato]platinum(II) complexes (1a, n = 10; 1b, n = 12; 1c, n = 14) was prepared by treating [PtCl2(CH3CN)2] with the corresponding N,N'-bis[(1H-imidazol-2-yl)methylene]-1,ω-alkanediamines. The trans coordination and vaulted structures of 1 have been unequivocally established from X-ray diffraction studies. When the concentration of a clear homogeneous solution of 1a-c in organic solvents increases from the diluted to the saturated state, the emission intensity and quantum efficiency increase continuously without concentration quenching at ambient temperature. This is in contrast to the emission profiles of other analogues 2-4 and typical AIEgens, which show ordinary concentration quenching under the same measurement conditions. The present concentration-driven emission enhancement is observed more intensely in a solution of a racemic mixture of 1 in comparison to that of the optically pure solution. Kinetic studies, 1H NMR, XRD analyses, and DFT calculations revealed that this specifically intense emission enhancement of 1 is attributed to an increase in the contribution of a 3MMLCT to 1GS transition, which is caused by the specific ability for the formation of a cofacial association dimer of 1.

Dalton Trans ; 45(48): 19257-19268, 2016 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-27891543


The participation of neighbouring nitrogen lone pairs in the chromogenic control of trans-bis(salicylaldiminato)Pt(ii) platforms was examined, using newly designed Pt analogues bearing salicylaldehyde hydrazone ligands. A series of non-vaulted and vaulted Pt complexes (1-5) with salicylaldehyde hydrazones as trans-coordinated bidentate ligands were synthesized and characterized with regard to the chromogenic behaviour of the trans-bis(salicylaldiminato)Pt(ii) coordination platforms. X-ray diffraction and 2D NMR data demonstrated that, in the case of the non-vaulted N-monomethyl complexes 1, there was significant participation of neighbouring N(2) lone pairs in the d-π conjugation of the trans-bis(salicylaldiminato)Pt(ii) platforms owing to conformational fixation arising from intramolecular hydrogen bonding. In contrast, the lone pairs of the N,N-dimethyl analogues 2 made a much less significant contribution to the extension of the d-π conjugation, due to their high conformational mobility. Complexes 1-5 were found to have structure-dependent chromogenic properties in the solution state, such that the absorption spectra of the N-methyl, short-vaulted complexes 1 and 3 exhibited significant hypsochromic shifts relative to the N,N-dimethyl, long-vaulted analogues 2 and 5, which had spectra very similar to that of the trans-bis(salicylaldiminato)Pt(ii) complex 6. The introduction of MeO groups at the 3- and 5 positions on the aromatic rings of 1 and 2 gave rise to significant hypsochromic and bathochromic shifts, respectively. In addition, νmax - ET(30) plots for various solvents revealed that complexes 1-5 exhibit negative solvatochromism, in which the data obtained in alcoholic solvents are hypsochromically separated from those in non-alcoholic solvents for 1 and 3, an effect that is not observed for 2 and 5. Complexes 1-5 also exhibit emission enhancement upon addition of excess CH3SO3H in dimethyl sulfoxide, and a significant effect of the linker on quantum yields (Φ77 K) was observed in the case of the vaulted complexes. Density functional theory calculations (B3LYP/6-31G*, LanL2DZ) determined that the structure dependence of the chromogenic behaviour of these non-vaulted and polymethylene-vaulted hydrazone complexes can be attributed to variations in the participation of neighbouring nitrogen lone pairs in the d-π conjugation on the trans-bis(salicylaldiminato)Pt(ii) coordination platforms.