Narrow Results

The demand for better tools for machining printed circuit boards (PCBs) is increasing due to the extensive usage of these boards in digital electronic products. This paper is aimed at optimizing coating type on micro drills in order to extend their lifetime in PCB machining. First, the tribotests involving micro crystalline diamond (MCD), nano crystalline diamond (NCD) and bare tungsten carbide (WC-Co) against PCBs show that NCD–PCB tribopair exhibits the lowest friction coefficient (0.35) due to the unique nano structure and low surface roughness of NCD films. Thereafter, the dry machining performance of the MCD- and NCD-coated micro drills on PCBs is systematically studied, using diamond-like coating (DLC) and TiAlN-coated micro drills as comparison. The experiments show that the working lives of these micro drills can be ranked as: NCD$>$TiAlN$>$DLC$>$MCD$>$bare WC-Co. The superior cutting performance of NCD-coated micro drills in terms of the lowest flank wear growth rate, no tool degradation (e.g. chipping, tool tipping) appearance, the best hole quality as well as the lowest feed force may come from the excellent wear resistance, lower friction coefficient against PCB as well as the high adhesive strength on the underneath substrate of NCD films.

In this paper, we have investigated electronic absorption, magnetic circular dichroism, fluorescence, and phosphorescence spectra for a protonated form of H₂TPPS₄(H₄TPPS₄) and the J-aggregates of H₄TPPS₄. The J-aggregation induces a large red-shift in the B (Soret) and Q absorption bands, while the phosphorescence peaks of H₄TPPS₄ and its J-aggregates are almost entirely similar. The large red-shift of the B-band is quantitatively explained by the exciton interactions. Thus, the exciton interactions in the J-aggregates are proposed as a useful approach to decrease the energy splitting between the fluorescent and phosphorescent states.

A presence of bulky 2,6-di-iso-propylphenoxy groups in bis-tert-butylisocyano adduct of 2(3),9(10),16(17),23(24)-tetrachloro-3(2),10(9),17(16),24(23)-tetra(2,6-di-iso-propylphenoxy)-phthalocyaninato iron(II) complex allows separation of two individual positional isomers and a mixture of the remaining two isomers using conventional chromatography. X-ray structures of “$D_{2h}$” and “$C_{4h}$” isomers were confimed by X-ray crystallography. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations of each individual positional isomer allowed insight into their electronic structures and vertical excitation energies, which were correlated with the experimental UV-vis and MCD spectra.

A reaction between 5,10,15,20-tetra(4-hydroxyphenyl)porphyrin and 1-bromopyrene resulted in the formation of 5,10,15,20-tetra[4-(4-(pyrenyl-1)butoxy)phenyl]porphyrin (1), while cross-condensation between 4-(4-(pyrenyl-1)butoxy)benzaldehyde, ferrocenecaboxaldehyde, and pyrrole resulted in the formation of 5-ferrocenyl-10,15,20-tri[4-(4-(pyrenyl-1)butoxy)phenyl]porphyrin (2), 5,10-diferrocenyl-15,20-di[4-(4-(pyrenyl-1)butoxy)phenyl]porphyrin (3), and 5,15-diferrocenyl-10,20-di[4-(4-(pyrenyl-1)butoxy)phenyl]porphyrin (4). All pyrene-containing porphyrins were characterized by ¹H NMR, UV-vis, MCD, and high-resolution ESI methods, while their electronic structures and the nature of the excited states were elucidated using density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. The molecular structure of 1 and its fluorescence quenching upon the addition of C${}_{60}$ fullerene was also investigated using X-ray crystallography and steady-state fluorescence approaches.

A metal-free meso-tetrakis($p$-methoxycarbonylphenyl) N-confused porphyrin (1) was prepared as the precursor for water-soluble derivatives by the reaction between pyrrole, methyl-4-formylbenzoate, and MSA. Tautomeric behavior of the porphyrin 1 in polar and non-polar solvents was probed by ${}^{\mathrm{\text{1}}}$H NMR, UV-vis, MCD, steady-state fluorescence, and high-resolution ESI methods and was found to be similar to the previously reported metal-free N-confused porphyrins. The electronic structure and the nature of the excited states in 1 were correlated with the results obtained by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations.

Three water-soluble quaternized metal-free tetra-(3-pyridyl)bacteriochlorins were synthesized and characterized by UV-vis, MCD, and NMR spectroscopy as well as elemental analysis. DFT calculations are indicative of the $\mathrm{\Delta }$HOMO $<$$\mathrm{\Delta }$LUMO relationship, which correlates well with the experimentally observed by MCD spectroscopy for all bacteriochlorins “reversed” sign sequence in the Vis-NIR region. TDDFT calculations also correctly predict large splitting between the $Q_x$ and $Q_y$ bands as well as splitting of the Soret band observed experimentally in all bacteriochlorins.

meso-Tetra(3,4,5-trimethoxy)phenyl-porphyrin and -tetrabenzoporphyrin and their phosphorus complexes were synthesized and their electronic absorption and magnetic circular dichroism (MCD) spectra discussed based on TD-DFT molecular orbital (MO) calculations. Nucleus-independent chemical shift (NICS) and anisotropy of the induced current density (ACID) calculations were also carried out for metal-free (and phosphorus) tetrabenzoporphyrins in order to discuss the aromaticity and flow of electrons in the molecule.

Nitration of 2,7,12,17-tert-butylporphycene, leading mainly to meso-substituted 9-nitro- and 9,20-nitro- derivatives, also yielded a small amount of porphycene bearing three tert-butyl moieties and the nitro group at the $\beta$ position. The electronic absorption spectra of 2-nitro and 9-nitroporphycenes are similar, but the photophysical characteristics strongly differ. Unlike the meso-substituted derivative, 2-nitroporphycene emits intense, long-lived (ns) fluorescence. Strong enhancement of fluorescence intensity is due to the absence of steric interactions between tert-butyl and nitro moieties. The two porphycenes also differ in their tautomeric properties. 2-nitroporphycene exists in one trans-tautomeric form, whereas two trans-tautomers of similar energies coexist in the meso derivative. These results are well reproduced by quantum-chemical calculations. The possibility of changing photophysics and tautomerism by shifting the position of the substituent may be exploited while designing porphycenes targeted for specific applications, such as photodynamic therapy or building molecular switches.

The elusive PcFe(DABCO)₂ (Pc = phthalocyaninato(2-) ligand; DABCO = 1,4-diazabicyclo[2.2.2]octane) complex was prepared and characterized by UV-Vis, MCD, ¹H NMR, and Mössbauer spectroscopies. The X-ray crystal structure of this complex indicates the longest Fe-N(DABCO) bond distance among all known PcFeL₂ complexes with nitrogen donors as the axial ligands. The target compound is only stable in the presence of large access of the axial ligand and rapidly converts into the (PcFe)₂O $\mu$-oxo dimer even at a modest temperature. The electronic structure of the PcFe(DABCO)₂ complex was elucidated by DFT and TDDFT methods. The DFT calculations predicted a very small singlet-triplet gap in this compound. The femtosecond transient absorption spectroscopy is indicative of extremely fast ($\sim$200 fs) deactivation of the first excited state in PcFe(DABCO)₂ with a lack of formation of the long-lived low-energy triplet state.