Faktor yang perlu diberi perhatian bagi bahan pemeka foto yang baik adalah keamatan serapan dan kedudukan serapan spektrum elektronik dalam julat cahaya nampak, keupayaan redoks dan kestabilan-fotonya. Kompleks molibdenum ditiolena dengan formula am [MoTp*(NO)(L)] dengan Tp* = tris(3,5-dimetilpirazolil)hidroborat dan L = toluena-3,4-ditiolat (L1); 1,2-benzenaditiolat (L2); 3,6-dikloro-1,2-benzenaditiolat (L3) didapati mempunyai sifat-sifat kimia dan fizik yang diperlukan untuk dijadikan sebagai anod pemeka-foto-elektron untuk sel foto-elektrokimia penguraian molekul air kepada hidrogen dan oksigen. Kompleks Mo-ditiolena yang disintesis daripada prekursor [MoTp*(NO)(I)2] dan sebatian ditiol dengan kehadiran Et3N sebagai agen penurunan dan penyahprotonan telah diciri dengan menggunakan kaedah analisis mikro unsur CHNS, spektroskopi IR, ultra-lembahyung dan cahaya nampak (UV-Vis), dan elektrokimia. Puncak penyerapan UV-Vis (λmax/ nm) dikesan pada 321-331, 369-372, 576-589 dan 736-741nm. Sifat keaktifan fotokimia dan foto-fizik turut dikaji bagi menentukan kesesuaiannya sebagai bahan pemeka foto bagi sel foto-elektrokimia. Ujian kestabilan-foto menunjukkan tiada berlaku penguraian terhadap ketiga-tiga kompleks tersebut selepas sinaran cahaya selama 24 jam.
A novel bimetallic double thiocyanate-bridged ruthenium and tungsten metal complex containing bipyridyl and dithiolene co-ligands was synthesized and the behavior of the complex as a dye-sensitizer for a photoelectrochemical (PEG) cell for a direct water splitting reaction was investigated. The ligands and metal complexes were characterized on the basis of elemental analysis as well as uv-Vis, Fourier transform infrared ( Pim) and nuclear magnetic resonance (11I and 13C NMR) spectroscopy. Cyclic voltammetry of the bimetallic complex showed multiple redox couples, in which half potentials E 112 at 0 .625 , 0.05 and 0.61 V were assigned as the formal redox processes of Ru(III)IRu(II) reduction, W(IV)IW(V) and W(V)IW(VI) oxidations, respectively. Photocurrent measurements were performed in homogeneous system and TiO2 was used as the photoanode for photocurrent measurements. Current density generated by the bimetallic complex was higher than that of N3 commercial dye which suggested that the bimetallic complex donated more electrons to the semiconductor.
Sifat-sifat kimia dan fizik kompleks tungsten nitrosilditiolena dengan formula am [WTp*(NO)(L)] dengan Tp* = tris(3,5- dimetilpirazolil)hidroborat dan L = toluena-3,4-ditiolat (L1), 1,2-benzenaditiolat (L2), 3,6-dikloro-1,2-benzenaditiolat (L3), telah dikaji untuk dijadikan pemeka foto bagi elektrod anod untuk sel fotoelektrokimia. Kompleks tungsten nitrosilditiolena disintesiskan dan diciri dengan menggunakan spektroskopi (IR) dan ultra-lembahyung dan cahaya nampak (UV-Vis) dan analisis mikro unsur CHNS. Teknik voltametri berkitar (CV) telah digunakan untuk menentukan keupayaan redoks kompleks
dan seterusnya aras jalur tenaga telah ditentukan daripada data yang diperoleh. Ketiga-tiga kompleks menunjukkan jurang jalur tenaga dalam julat 1.59 – 1.63 eV. Jurang jalur tenaga yang dikira daripada analisis CV adalah bersepadan dengan anggaran daripada spektrum serapan elektronik kompleks. Berdasarkan gambar rajah jalur tenaga, ketiga-tiga kompleks dijangka mempunyai potensi untuk digunakan sebagai pemeka foto bagi fotoelektrod sel fotoelektrokimia.
A benzoylthiourea molecule namely 1,1-dibenzyl-3-(2-bromobenzoyl)thiourea (2BrBT) was synthesized and characterized
by C, H, N and S elemental, mass spectrometry and spectroscopic analyses (infrared, ultraviolet-visible and nuclear
magnetic resonance). The 2BrBT compound crystallized in a tetragonal system with the space group P43 and exhibits
an acentric crystalline packing due to the presence of intermolecular H-bonding network that forms a self-assembly
of 1D helical motif. The asymmetric delocalisation of electrons in the molecule retains its transparency throughout the
visible and near-infrared region and hence, essentially propagates the macroscopic helical motif in the solid state. The
highest-occupied and lowest-unoccupied molecular orbital (HOMO/LUMO) are mainly found on the thiourea moiety and
the benzoylthiourea fragment, respectively and shows an optical bandgap of 3.50 eV. The influence of its geometrical
characteristics to the optical properties of 2BrBT is established and discussed in view of nonlinear optical (NLO)
application.
The presence of two different chromophores in benzothiazole molecule namely benzothiazole and aromatic rings lead to
interesting chemical and biological properties that attract more researches on the compounds. Three new benzothiazolylbenzoythiourea
compounds namely 1-(1,3-benzothiazol-2-yl)-3-(benzoylthiourea) (BBT), 1-(1,3-benzothiazol-2-yl)-3-
(4-chlorobenzoylthiourea) (BBT-4Cl) and 1-(1,3-benzothiazol-2-yl)-3-(4-methoxybenzoylthiourea) (BBT-4OCH3
) with
different electron withdrawing substituents (R) at the para positions on the benzene ring of benzoylthiourea ring have
been synthesized from the reaction of R-benzoyl isothiocyanate (R= H, Cl, and OCH3
) and 2-aminobenzothiazole. The
compounds were characterized by spectroscopic techniques (infrared, 1
H proton NMR and UV-Vis). The IR spectra showed
the frequency signals of n (C=O), n (C=S), n (N-H) at 1664-1673, 1238-1249 and 3031-3055 cm-1, respectively. The 1
H
proton NMR spectra showed the presence of N-H amine and amide signals in the region of (12.14-12.35) and (14.17-14.43)
ppm, respectively. The proton signals of the two benzothiazole and benzoylthiourea moieties appear at 7.08-8.16 ppm.
A theoretical study based on Density Functional Theory (DFT) and Time-Dependent (TD) DFT was conducted to optimize
the geometrical structure and investigate the electronic properties of title compounds. The highest occupied molecular
orbital (HOMO) was found on the benzothiazole moiety; while, the lowest-unoccupied molecular orbital (LUMO) was
located at the benzoylthiourea fragment. The DFT optimized structures possessed an intramolecular hydrogen bonding
and the types of para substituents used influenced the properties of hydrogen bonding.
Aroylthiourea ligands, 1-aroyl-3-cyclohexyl-3-methylthiourea (HL1
), 1-(2-chloroaroyl)-3-cyclohexyl-3-methylthiourea
(HL2
), 1-(3-chloroaroyl)-3-cyclohexyl-3-methylthiourea (HL3
) and 1-(4-chloroaroyl)-3-cyclohexyl-3-methylthiourea
(HL4
) were synthesized through a condensation reaction of methylcyclohexylamine and aroylisothiocyanate with a
general formula (X-Ph)(CO)NH(CS)N(C6
H5
)(CH3
) where X = H, o-Cl, m-Cl and p-Cl, fully characterized by CHNS micro
elemental analysis, infrared spectroscopy, UV-visible, nuclear magnetic resonance (1
H, 13C) and X-ray crystallography.
1-(3-chloroaroyl)-3-cyclohexyl-3-methylthiourea (HL3
) crystallized in the monoclinic system, a=14.504(3), b=4.9599(11),
c=22.325(5) Å, β=98.461(7)°, Z= 4 and V=1588.5(6) Å with space group P21
/c. The IR spectra of the ligands exhibits
the characteristic v(CO) and v(N-H) at range 1701-1640 cm-1 and 3317-3144 cm-1, respectively. Whereas the 1
H and 13C NMR spectra shows the resonances for N-H and -CO groups at range 8.3-8.5 and 160-163 ppm, respectively. A onepot reaction involving the aroylthiourea ligand, oxovanadium(IV) ion and potassium hydrotris(3,5-dimethylpyrazolyl)
borate (KTp*) complex gave the desired [oxovanadium(IV)(tris(pyrazolyl)borate)(aroylthiourea)] complexes namely
Tp*VOL1
, Tp*VOL2
, Tp*VOL3
and Tp*VOL4
and all complexes were characterized accordingly. X-ray study showed that
Tp*VOL1
adopted a monoclinic crystal, a=3.415(2), b=19.463(3), c=14.22(3) Å, β=107.411(4)°, Z= 4 and V=3542.7(11)
Å with P21
/c space group. The VO2+ center adopted a pseudo-octahedral geometry O2N3S, with the oxovanadium(IV)
coordinated to the bidentate ligand (X-Ph)(CO)NH(CS)N(C6
H5
)(CH3
) and tridentate Tp* ligands. The results showed
that aroylthiourea ligands behave as bidentate chelate through O and S atom and the Tp* C3v symmetry adds stabilization
to the VO2+ through its protective tripodal geometry.