Tong-Ing Ho

Substituent effects on intramolecular charge-transfer behaviour of styrylheterocycles

To understand the influence of substituents on intramolecular charge transfer (ICT), absorption and emission spectra were measured for several derivatives of 2-styrylquinoline (2-StQ), 2-styrylpyridine (2-StP) and 2-styrylthiophene (2-StT) systems. A strong donor, such as an N,N-dimethylamino group can produce an ICT compound in these systems, and the excited state dipole moments were measured using a solvatochromic method. Quinoline and pyridine can only act as acceptors. Depending on substituents, the thiophene ring could be a donor or an acceptor. For same donor in our systems, the strength order of different acceptors is quinoline>naphthalene>pyridine>thiophene. Besides electronic effect, steric conformation is also an important factor in ICT molecules. Protonation and hydrogen bonding at acceptor site show red-shift in absorption maxima. The degree of shift depends on the substituents. Interaction at a donor site gives the opposite result. There is a linear relation between excited state dipole moments and absorption energy.

Excited state proton transfer and steric effect on the hydrogen bonding interaction of the styrylquinoline system

Abstract The influence of hydrogen bonding (HB) and protonation on an intramolecular charge transfer (ICT) compound, such as p-N , N -dimethylamino-2-styrylnaphthalene (2-StN-NMe 2 ), p-N , N -diethylamino-2-styrylnaphthalene (2-StN-NEt 2 ), p-N , N -dimethylamino-2-styrylquinoline (2-StQ-NMe 2 ) and p-N , N -diethylamino-2-styrylquinoline (2-StQ-NEt 2 ), in the ground and excited state is investigated. The steric effect of HB on ICT compounds is studied in different protic acids. The steric and ICT effect will weaken the HB ability of the N , N -diethylamino site and enhance the HB ability of the quinoline site in 2-StQ-NMe 2 . The excited state proton transfer (ESPT) occurred in the HB complex of 2-StQ-NMe 2 . The excited state deprotonation (ESDP) process was observed for the double protonation form of 2-StQ-NMe 2 in 2,2,2-trichloroethanol (TCE). The influence between the HB interaction and protonation could be separated for the first time by using another strong base.

Synthesis and molecular structure of novel zinc(II) complexes: [{Zn(HL)Cl2}n], [Zn2L2Cl2] and [Zn2(µ-OH)LCl2][HL = 4-methyl-2,6-bis(pyrazol-1-ylmethyl)phenol]

The synthesis of a new bifunctional ligand, 4-methyl-2,6-bis(pyrazol-1-ylmethyl)phenol (HL), and the structures of its complexes with zinc(II) are described. The ligand reacts with zinc chloride to form a macromolecular complex, [{Zn(HL)Cl2}n]1. In basic solution two binuclear zinc(II) complexes, [Zn2L2Cl22, and [Zn2(µ-OH)LCl2]3, are formed under different reaction conditions. The molecular structures of complexes 1 and 2 have been characterized by X-ray diffraction: 1, monoclinic, space group =P21/c, Z= 4, a= 12.357(2), b= 12.400(2), c= 14.957(4)A, β= 100.18(2)°; 2, triclinic, space group =P, Z= 1, a= 9.194(1), b= 10.040(1), c= 10.316(2)A, α= 114.40(2), β= 115.93(2), γ= 89.16(1)°. The co-ordination sphare of zinc(II) in complex 1 is tetrahedral, in 2 it is distorted square pyramidal.

A convenient method of measuring quantum yields of photoisomerization of trans-stilbene

Abstract A novel and convenient method of measuring quantum yields of photoisomerization of trans -stilbene was developed by using a monochromic nitrogen laser light source and a pulsed energy meter. The method has high accuracy without the need to employ chemical actinometers.

Efficient photocycloaddition of phenanthroquinones with simple olefins

Abstract A series of substituted phenanthroquinones (PQ’s) was prepared, their phosphorescence spectra and decay rate constants, cyclic voltammograms, and photoreaction in the presence of tetramethylethylene (TME) were investigated. With 450xa0nm irradiation their triplet excited state cyclized with TME to give the corresponding dioxenes, 2′,2′,3′,3′-tetramethyl-1′,4′-dioxa-1′,2′,3′,4′-tetrahydrotriphenylene, cleanly and much faster than that with 300xa0nm irradiation. The pattern of the reaction was effected weakly in random fashion by the substituent at the 3-position of PQ’s. The photocycloaddition, as exemplified by PQ itself, is so efficient that it occurred even by room light and during optical spectroscopic recordings; its limiting quantum yield in benzene is established to be unity with 450xa0nm irradiation. It owes the unusual efficiency to a long lifetime of the PQ triplet excited state with the n – ∗ π configuration, and to the successful cyclization in every diffusion controlled collision as implicated by TME quenching of PQ phosphorescence intensity in CCl 4 solution. The triplet excited state reaction was supported by competitive quenching of the dioxene formation by triplet quenchers as well as by oxygen. These PQ’s do not fluoresce in solution, but show phosphorescence in solid solution with lifetimes of about 10xa0ms and in CCl 4 solution with lifetimes in the order of 100xa0μs in the room temperature range. PQ’s with 3-cycano, 3-chloro, 3-methoxy, and without substitutions photocyclized to cyclohexene to give the corresponding dioxenes with small stereochemical scrambles, that was interpreted that the extent of electron transfer in the 1,6-diradical stage is small. Similar photocycloadditions to isobutene gave a 1:1 mixture of two regio-isomers, this was taken as evidence for a direct radical attack on olefins to give 1,6-diradical intermediates.

Synthesis, properties and molecular structures of iron(III), cobalt(II), nickel(II), copper(II), copper(I) and zinc(II) complexes with N,N-bis(pyrazol-1-ylmethyl)benzylamine

A newly prepared ligand, N,N-bis(pyrazol-1-ylmethyl)benzylamine (L) reacted with metal ions to form [FeLCl3], [NiL(NCS)2(MeOH)], [MLX2](M = CoII, CuII or ZnII, X = Cl–, Br– or NCS–) and [(CuLI)2]. The crystallographically determined structures of [CoLCl2] and [CoL(NCS)2] reveal the co-ordination sphere of cobalt(II) to be intermediate between distorted tetrahedral and trigonal bipyramidal. In [NiL(NCS)2(MeOH)] the co-ordination sphere of nickel(II) ion is distorted octahedral while that of copper(II) in [CuLCl2] is distorted square pyramidal. The complex [(CuLI)2] displays distorted tetrahedral geometry around copper(I), and [ZnLBr2] shows distorted tetrahedral geometry around zinc(II).

Phenanthrene-olefin exciplexes. Substituent effects

Abstract The reductive and oxidative fluorescence quenching of the 3-substituted phenanthrenes (Xue5fcH, CN, Cl, Br, CH3, (CH3)2CH, CH3O) by amines, dimethyl fumarate and fumaronitrile were studied. Fluorescent exciplexes are observed for dimethyl fumarate and fumaronitrile systems in benzene at room temperature. The maximum fluorescence energies can be correlated with Rehm and Weller theoretical calculations. The systematic shifts in exciplex energies also correlate linearly with the Hammett σp constants. Linear correlations are also observed between the quenching constants kq and the Hammett σp constants for amine quenching. A simple frontier molecular orbital theory is proposed for the linear correlation of exciplex fluorescence. The effect of the substituent on the lifetime of the exciplexes was also investigated.

Synthesis and characterization of tetraaniline-containing copolymer

Preparation of ditetraaniline-capped copolymer with a narrow polydispersity index (1.1) was demonstrated. This new material possessed excellent film-flexibility and comparable electrical conductivity to tetraaniline.

Synthesis and characterization of tetraaniline-terminated starburst poly(urethane-urea)

Novel tetraaniline-terminated starburst poly(urethane-urea), utilizing fullerenol as a molecular core, was synthesized. It exhibited a narrow branching distribution of six polymer arms on average.

Synthesis, properties and molecular structures of cobalt(II), copper(II) and zinc(II) complexes with 1,2-bis[3-(pyrazol-1-yl)-2-oxapropyl]benzene

Abstract The new ligand 1,2-bis[3-(pyrazol-1-yl)-2-oxapropyl]benzene (L), reacted with cobalt(II) chloride, copper(II) chloride and zinc(II) chloride to form [CoLCl 2 ], [CuLCl 2 ], and [ZnLCl 2 ], respectively. The structures of these metal complexes have been determined by X-ray crystallography. The Co and Zn structures are isomorphous with distorted tetrahedral metal geometries. The coordination sphere of the copper(II) ion in its complex is intermediate between distorted tetrahedral and distorted square-pyramidal geometry, if a weak Cu … O interaction is taken into account.