Fluorescence Properties of Phenol-Modified Zinc Phthalocyanine that Tuned by Photoinduced Intra-Molecular Electron Transfer and pH Values

Tetra[α-(4-hydroxyphenoxy)] zinc phthalocyanine, ZnPc(α-OPhOH)₄, was synthesized and its photophysics was found to be sharply pH dependent. Dual fluorescence emission around 700 nm was observed when it is dissolved in basic solution. The fluorescence of the phthalocyanine can be sharply switched off at pH 9.1 due to the intramolecular photoinduced electron transfer (PET) in ZnPc(α-OPhONa)₄, formed by the deprotonation of ZnPc(α-OPhOH)₄. The photophysics of both ZnPc(α-OPhOH)₄ and ZnPc(α-OPhONa)₄ were studied in detail by UV-vis absorption, steady state and time-resolved fluorescence and transient absorption (TA) to reveal the fluorescence quenching mechanism. Intra-molecular PET in ZnPc(α-OPhONa)₄ from the donor, PhONa subunits, to the acceptor, ZnPc moiety, was characterized by the much smaller fluorescence quantum yield (0.003) and lifetime (<0.20 ns). PET was further evidenced by the occurrence of charge separation state (CSS) in TA spectra, i.e. the bands due to anion radical of ZnPc and phenol radical. The lifetime of the charge separation state is ca. 3 ns, the efficiency of PET is ca. 99% and the rate constant of PET is 2.3 × 10¹⁰ s⁻¹.     

Synthesis and photophysical behavior of a novel zinc phthalocyanine containing a single carboxylic acid and three phenylthio substituents

Zinc 2, (3)-tri-(phenylthio)-2, (3)-carboxy phthalocyanine (ZnPc(COOH)(SPh)₃), zinc 2, (3)-tetra-(phenylthio) phthalocyanine (ZnPc(SPh)₄) and 2, (3)-tetra-(phenylthio) phthalocyanine (H₂Pc(SPh)₄) were synthesized and their photophysical behavior were compared with those of a number of zinc phthalocyanine (ZnPc) derivatives. ZnPc(COOH)(SPh)₃ and ZnPc(SPh)₄ had similar fluorescence (Φ_F=0.14) and triplet state (Φ_T=0.65) quantum yields in dimethylsulfoxide, hence showing no effects of the replacement of one of the phenylthio groups with a carboxylic acid group. ZnPc(COOH)(SPh)₃ displayed a slightly shorter triplet lifetime (τ_T=331 μs) than ZnPc (τ_T=350 μs) in DMSO, but within the range of ZnPc derivatives. The triplet lifetime for ZnPc(COOH)(SPh)₃ is much longer than for the symmetrical derivative (ZnPc(SPh)₄) with τ_T=149 μs in DMSO.     

High performance organic planar heterojunction solar cells by controlling the molecular orientation

A highly efficient planar heterojunction OSC based on zinc phthalocyanine (ZnPc)/fullerene (C₆₀) by controlling the orientation of the ZnPc by using copper iodide (CuI) as the interfacial layer is reported. The proportion of face-on ZnPc molecules was increased significantly on the CuI layer compared to the layer without the CuI layer, which was analyzed with wide-angle X-ray scattering (WAXS) and optical absorption. The power conversion efficiency (PCE) of the orientation controlled planar heterojunction OSC was remarkably enhanced to 3.2 ± 0.1% compared with 1.2 ± 0.1% of the conventional OSCs without the control of the molecular orientation. By inserting the 3-nm-thick CuI layer, J_SC, V_OC and FF have increased from 4.6 ± 0.2 to 8.9 ± 0.2 mA cm^?2, from 0.48 ± 0.01 to 0.59 ± 0.02 V, and from 0.56 ± 0.01 to 0.61 ± 0.02, respectively. V_OC enhancement is discussed with the result of the ultraviolet photoemission spectra (UPS) measurements.     

14N NMR in NH4I and NH4Br

¹⁴N magnetic resonance data show that the α → β transition in NH₄I is connected with a discontinuous change in the ¹⁴N chemical shift, Δδ = 20.5 ppm, whereas the order-disorder type β(O_h) → γ(D_4h) transition is accompanied by a small quadropole splitting of the ¹⁴N spectrum. A quadrupole splitting of the ¹⁴N line was as well found in the tetragonal “antiferromagnetically” ordered γ-phase of NH₄Br, but not in the “ferromagnetically” ordered δ(T_d) phase of NH₄Cl.     

Investigation of electrical properties (ac and dc) of organic zinc phthalocyanine,ZnPc, semiconductor thin films

We report measurements on the electrical properties of thermally evaporated zinc phthalocyanine, ZnPc, semiconductor thin films. Aluminum and gold metal electrodes were used and both proved to act as ohmic contacts. A relative permittivity, ε_r, of 1.56 was estimated from the dependence of capacitance on film thickness. The room temperature current density–voltage measurements indicated an ohmic conduction at low voltages, while a space–charge-limited conduction at higher voltages. An average value of a thermally generated hole concentration of the order 10¹³ m⁻³ was estimated at room temperature.The ac conductivity, capacitance and loss tangent were measured over a wide range of temperature (from 170 to 430 K) and frequency (between 0.1 and 20 kHz). The ac conductivity of ZnPc films was observed to be proportional to ω^s, where ω is the angular frequency, and the index s is a temperature and frequency-dependent constant. At low temperatures and for higher frequencies the ac conduction was due to hopping. The capacitance, as well as the loss tangent, was found to be dependent on both temperature and frequency, but was constant for all frequencies at low temperatures. Such dependences were accounted for the equivalent-circuit model consisting of inherent capacitance in parallel with a temperature dependent resistive element.     

Structural and electrical properties of the α-form of metal-free phthalocyanine (α-H2Pc) semiconducting thin films

An X-ray structural study of thermally evaporated metal-free phthalocyanine thin films with various film thicknesses was performed. All samples studied had polycrystalline structure and the unit cell was found to be of the α-form. Variation of the deposition rate from 0.5 to 1 nm s⁻¹ had little effect on the structure. The films exhibit preferential orientation at low thickness; however, at higher thickness they become less orientated as additional peaks appear in the spectrum. The increase in the intensity of the first significant low angle peak with increasing thickness is attributed to the increased volume of the crystal probed during the X-ray exposure.The current density–voltage (J–V) characteristics of α-H₂Pc films sandwiched between two aluminum electrodes showed ohmic behavior at low voltages and space–charge-limited conduction (SCLC) at higher voltages. For comparison, similar measurements of the current density as a function of voltage were performed on zinc phthalocyanine, ZnPc, thin films using aluminum electrodes. The J–V characteristics showed ohmic behavior at low voltages followed by SCLC dominated by an exponential trap distribution at higher voltages. Consequently, in both H₂Pc and ZnPc films, aluminum electrodes act as if they are ohmic contacts. The implied provision of ohmic contacts using aluminum in this case is attributed to the formation of a thin Al₂O₃ layer during the deposition process.     

Photofunctional Polyurethane Nanofabrics Doped by Zinc Tetraphenylporphyrin and Zinc Phthalocyanine Photosensitizers

Polymeric polyurethane nanofabrics doped by zinc tetraphenylporphyrin (ZnTPP) and/or zinc phthalocyanine (ZnPc) photosensitizers were prepared by the electrospinning method and characterized by microscopic methods, steady-state and time-resolved fluorescence, and absorption spectroscopy. Nanofabrics doped by both ZnTPP and ZnPc efficiently harvest visible light to generate triplet states and singlet oxygen O₂(¹Δ_g) with a lifetime of about 15 μs in air atmosphere. The energy transfer between the excited singlet states of ZnTPP and ground states of ZnPc is described in details. All nanofabrics have bactericidal surfaces and photooxidize inorganic and organic substrates. ZnTPP and ZnPc in the polyurethane nanofabrics are less photostable than incorporated free-base tetraphenylporphyrin (TPP).     

On theg-value shift and intersystem crossing in photo-excited radical-triplet systems

The electron paramagnetic resonance (EPR) signals of photoexcited quartet (Q₁) states for zinc(II) tetra-tert-butyl-phthalocyanine (ZnPc) ligated by 3- and 4-(N-nitronyl-nitroxide) pyridine radicals (3-NOPy, 4-NOPy) were observed in toluene solution at room temperature by means of X-band (9.4 GHz) time-resolved EPR (TREPR) spectroscopy. Theg values of Q₁ in the ZnPc-3-NOPy and ZnPc-4-NOPy complexes were found to beg=2.0025 andg=2.0036, respectively. The obtainedg value (2.0036) for ZnPc-4-NOPy is in good agreement with the value (g=2.0037) of the Q₁ state calculated under the strong-exchange limit. Theg value (2.0025) is just an average of the Q₁ and D₁ (g=2.0013) states for ZnPc-3-NOPy. Theg value of Q₁ for zinc(II) meso-tetraphenylporphine (ZnTPP) ligated by 3-NOPy showed a slight shift (g=2.0027) at X-band and no shift (g=2.0031) at W-band from the calculatedg value (g=2.0031) (J. Fujisawa, Y. Iwasaki, Y. Ohba, S. Yamauchi, K. Koga, S. Karasawa, M. Fuhs, K. Möbius, S. Weber, Appl. Magn. Reson. 21, 483–493, 2001). These changes in theg value were found to originate from an averaging of the TREPR spectra over the Q₁ and photoexcited doublet (D₁) states via a fast intersystem crossing (ISC) process. The ISC rates between these two states were estimated by means of numerical calculations with the modified Bloch equations as 1.2·10⁸ and 6·10⁷ s^?1 for the ZnTPP-3-NOPy complex at the X- and W-bands, respectively. The lower limit of the ISC rate was obtained as 10⁹s^?1 for the ZnPc-3-NOPy complex and the higher limit was found to be 3.1·10⁸ s^?1 for the ZnPc-4-NOPy complex.     

Zeeman effect and stark splitting of the electronic states of the rare-earth ion in the paramagnetic terbium garnets Tb<Subscript>3</Subscript>Ga<Subscript>5</Subscript>O<Subscript>12</Subscript> and Tb<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>

The Zeeman effect in the ⁷ F ₆ → ⁵ D ₄ absorption band of the Tb³⁺ ion in the paramagnetic garnets Tb₃Ga₅O₁₂ and Tb₃Al₅O₁₂ was studied. The field dependences of the Zeeman splitting of some absorption lines are found to exhibit unusual behavior: as the magnetic field increases, the band splitting decreases rather than increases. Symmetry analysis relates these lines to 4f → 4f electron transitions of the doublet-quasi-doublet or quasi-doublet-doublet type, for which the field dependences of the splitting differ radically from the well-known field dependences of the Zeeman splitting for quasi-doublet-quasi-doublet or quasi-doublet-singlet transitions in a longitudinal magnetic field.     

Spectre d'absorption et effet Zeeman de l'ion Mn2+ dans un sulfate acide de manganese et de potassium MnK4H2(SO4)4, 2H2O a basse temperature

We present aborption spectra of an oriented single crystal of MnK₄H₂(SO₄)₄, 2H₂O at temperatures between 20 and 1.6 K. This salt has orthorhombic symmetry and gives, both in the visible and ultraviolet regions, an absorption spectrum which changes considerably when the temperature decreases from 20 to 4.2 K. The spectrum has sharp lines at 1.6 K in the two absorption regions corresponding to teh excited levels ⁴A₁⁴E(⁴G) and ⁴T₂(⁴D). A study has been made of the Zeeman splitting of these sharp lines; a discontinuity has been observed in the Zeeman splitting as a function of magnetic field at 1.6 K. This discontinuity is a consequence of a magnetically-ordered phase.     

The giant dipole resonance in 55Co

Recent measurements of the ⁵⁴Fe(p, γ)⁵⁵Co cross section indicate the existence of a splitting between the T_< and T_> components of the giant dipole resonance. We have calculated the (p, γ) cross section in the shell-model formalism. The bound-state interaction was determined by a fit to fp and sd shell nuclei. The calculation predicts the isospin splitting of ≈ 2.4 MeV and is consistent with all data in the energy region E_p = 9–15 MeV as well as the low-lying ⁵⁵Co spectrum.     

Measurement of the hyperfine structure splitting for the 4 and 52 P 1/2 states of sodium using radio-frequency spectroscopy

The hyperfine-structure splitting for the 4 and 5² P ^1/2 states of sodium was measured using step-wise laser excitation combined with rf-resonance techniques. The magnetic dipole interaction constants were found to be a(4² P _1/2)=30.4(5) MHz and a(5₂ P _1/2) =13.3(2) MHz. The results are compared with a theoretical calculation, taking polarization effects into account.     

Spektroskopische Untersuchungen an DyAsO4

DyAsO₄ undergoes a crystallographic phase transition atT _D=11.2K which is induced by a cooperative Jahn-Teller-effect. As deduced from the optical absorption spectra the distance between the two lowest lying Kramers doublets of the Dy³⁺ ion is increased from (6.1±0.5) cm^?1 aboveT _D to (25.0±0.5) cm^?1 at 4.2 K. BelowT _D the splitting factor of the lowest doublet becomes nearly uniaxial with a maximum value ofg _b =17.5±1.0 along the crystallographicb-axis. AtT _N=2.44 K the crystals order antiferromagnetically. The absorption lines of Er³⁺ ions in DyAsO₄ show already a splitting immediately belowT _D which is explained by magnetic short range ordering of the Dy³⁺ ions in the temperature rangeT _{N D} .     

Charge Transfer Photophysics of Tetra(α-amino) Zinc Phthalocyanine

The absorption, fluorescence, and transient absorption spectra of Tetra(α-amino) zinc phthalocyanine, ZnPc(α-NH₂)₄, have been measured in polar solvents and compared with that of ZnPc(α-R)₄ (R?=?H, NO₂, OCH(CH₃)₂). While the latter three showed the typical photophysics of phthalocyanines, ZnPc(α-NH₂)₄ exhibits distinct spectral properties, a very low fluorescence quantum yield and a relatively long fluorescence lifetime. These observations are explained by the substantial charge transfer characters in the absorption and fluorescence spectra of ZnPc(α-NH₂)₄. NMR indicates that intramolecular H-bonding makes atoms in NH₂ actually coplanar with other elements of ZnPc(α-NH₂)₄. The local excited state is non emissive and the weak emission is assigned to its charge transfer state. The transient absorption bands from laser flash photolysis located at 630 nm, 645 nm is assigned to the mono-charge transfer state, while that at 545 nm is assigned to the di-charge transfer state.     

Zeeman effect in the 4A22E pair states in the first nearest neighbour Cr(III) pair in ruby

The Zeeman splitting of the ⁴A⁴₂A₂ → ⁴A²₂E transitions in the first nearest neighbour Cr(III) pair in ruby is determined by excitation spectroscopy. Previous assignments are shown to be incorrect and evidence is presented for a large trigonal field.     

EPR study of the ferroelastic phase transition in CsLiSO4

EPR spectra of SO^-₃ ion-radical in X-ray irradiated CsLiSO₄ single crystals were used for the study of the ferroelastic phase transition at T_c = 203.0 K. The splitting (ΔH) of the SO₃ line in the low-temperature ferroelastic phase has been interpreted as proportional to the square of the order parameter. The splitting shows the temperature dependence ΔH ∞ (T_c ? T) 1.01^± 0.01     

An O23− radiation defect in AlPO4 and GaPO4

Hole centers with C₂ site symmetry, very similar g-matrices and small hyperfine splittings due to two nuclei with $\text{I =}\text{1}\text{2}$ were detected and analyzed by EPR in synthetic single crystals of AlPO₄ and GaPO₄ after X-ray irradiation. A very similar center, but without any detectable hyperfine splitting, was reported in natural quartz. These centers are ascribed to O₂^3? ions with two equivalent ³¹P nuclei as the source of the hyperfine splitting in the phosphates. This hyperfine splitting is considerably smaller than for O? adjacent to phosphorous (i.e. PO₄^2? centers). The electronic structures of these defects are discussed and compared with those reported for the same centers in other compounds.     

Trimeric metallo-phthalocyanines with good performances for nanosecond optical limiting in solution

Optical limiting (OL) performances of two trimeric metallo-phthalocyanines namely, 2,4,6-tris[2-oxa-9,10,16,17,23,24-hexa(hexylthio) phthalocyaninato M(II)]-s-triazine (M = Zn for compound ZnPc and Cu for compound CuPc) were investigated by using the Z-scan technique. The measurements were performed using collimated 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. OL parameters of the ratio of the excited state to ground state absorption cross-sections κ, the effective non-linear absorption coefficient β_eff, the linear absorption coefficient α₀, limiting threshold F_th and the saturation density or energy density F_sat values were determined for the investigated compounds. The results indicated that both compounds exhibited good OL performances. ZnPc shows slightly better OL parameters than that of CuPc.     

Dielectric characterization of semiconducting ZnPc films sandwiched between Gold or Aluminum electrodes

The dependencies of complex dielectric functions (the dielectric constant, ε ₁, and the dielectric loss, ε ₂), on frequency and temperature of zinc phthalocyanine (ZnPc) thin films sandwiched between either gold or aluminum Ohmic-electrode contacts have been investigated in the temperature range of 93–470 K and frequency range 0.1–20 kHz. It is found that both values of ε ₁ and ε ₂ decrease with increasing frequency and increase with decreasing temperature. The rate of change depends greatly on the temperature and frequency ranges under consideration. Around room temperature, neither ε ₁ nor ε ₂ show any appreciable change through the whole range of frequencies. Thus, the dielectric dispersion is found to include of both dipolar and interfacial polarizations. The dependencies of both dielectric functions on frequency at different temperatures were found to follow a universal power law of the form ω ⁿ , where the index 0<n≤?1. This indicates that the correlated barrier hopping (CBH) model is a suitable mechanism to describe the dielectric behavior in ZnPc films. Furthermore, the results of the dielectric response indicate that polarization in these films could be in the form of non-Debye polarization. However, the Debye polarization can be traced below room temperature. The obtained results of the relaxation-time, τ, dependency on temperature have shown that a thermally-activated process may be dominated in ZnPc thin films conduction at high temperatures. Partial phase transition (from α- to β-phase) has been observed around 400 K in molecular relaxation-time, τ, and optical dielectric constant, ε _∞. Arrhenius behavior has been observed for all the dielectric loss and conductivity relaxation-times above room temperature and their activation energies are explained and reported. The optical dielectric constant ε _∞ was found to increase with temperature.     

Optical and ESR spectra of the C4H radical in rare gas matrices at 4 K

C₄H (butadinyl) was trapped in Ar and Ne matrices at 4 K by the uv photolysis of a mixture of C₄H₂ and the rare gas. CC stretching and CH bending modes have been identified in the ir at 2060 and 735 cm^?1. A band system appearing in the 2500–3000 Å region with (0, 0) at 33 800 cm^?1 has been analyzed and tentatively assigned to a ²Π_r ← X²Σ transition. C₄D: Ar spectra confirm the optical assignments. The ESR spectrum exhibits a proton hyperfine splitting b = A_⊥(H) = 16.5 MHz, at g_⊥ = 2.0004(5). The spin-doubling constant, γ, is estimated to be +0.0006(2) cm^?1.