Dennis K. P. Ng

Organic Optical Limiter with a Strong Nonlinear Absorptive Response

Molecules with weak ground-state absorption that form strongly absorbing excited states can be used in optical limiters, which can protect sensors or human eyes from optical damage. Phthalocyanine complexes bearing heavy atoms or paramagnetic groups or in solvents containing heavy atoms show optical limiting enhanced by excited triplet-state absorption. A nonhomogeneous distribution of indium tetra(tert-butyl)phthalocyanine chloride along the beam path substantially enhances the excited-state absorption, yielding an optical limiter with a linear transmittance of 0.70 that can attenuate 8-nanosecond, 532-nanometer laser pulses by factors of up to 540.

Highly Efficient Energy Transfer in Subphthalocyanine−BODIPY Conjugates

Two novel subphthalocyanines substituted axially with a BODIPY or distyryl BODIPY moiety have been synthesized. Both systems exhibit a highly efficient photoinduced energy transfer process, either from the excited BODIPY to the subphthalocyanine core (for the former) or from the excited subphthalocyanine to the distyryl BODIPY unit (for the latter).

Phthalocyanine−Polyamine Conjugates as Highly Efficient Photosensitizers for Photodynamic Therapy

A series of silicon(IV) phthalocyanines substituted axially with different polyamine moieties have been prepared. Their fluorescence quantum yields (Φ(F) = 0.03-0.08) in N,N-dimethylformamide are low because of reductive quenching by the amino moieties. The values are significantly increased in aqueous media (Φ(F) = 0.12-0.21) as a result of protonation of the amino substituents. All the compounds are highly photocytotoxic against human colon adenocarcinoma HT29 cells and Chinese hamster ovary cells with IC(50) values as low as 1.1 nM. Flow cytometric studies of two selected compounds (2 and 5) against HT29 cells have shown that they induce apoptosis extensively. As shown by confocal microscopy, these two compounds also show high affinity toward the lysosomes, but not the mitochondria, of the cells. Their in vivo photodynamic activity has also been investigated using HT29 tumor bearing nude mice. Both of them can effectively inhibit the growth of the tumor without causing apparent injury to the liver of the mice.

Synthesis, spectroscopic and electrochemical properties of substituted bis(phthalocyaninato)lanthanide(III) complexes

Abstract The sandwich-like bis(phthalocyaninato)lanthanide(III) complexes Ln[Pc′(R) 8 ] 2 (Ln = Eu, Gd; Pc′ = 2,3,9,10,16,17,23,24-octasubstituted phthalocyaninate; R = H, n-C 7 H 15 , OC 5 H 11 ) have been prepared by treating Ln(acac) 3 ·nH 2 O (Ln = Eu, Gd; acac = acetylacetonate) with dilithium phthalocyaninate or with the corresponding disubstituted phthalonitriles in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The spectroscopic and electrochemical properties of the substituted sandwich complexes have been investigated and compared with those of the unsubstituted analogues. The matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) and electrospray ionisation mass spectrometry (ESI-MS) have also been employed to unambiguously characterise this novel class of compounds for the first time.

Mimicking Photosynthetic Antenna‐Reaction‐Center Complexes with a (Boron Dipyrromethene)3–Porphyrin–C60 Pentad

A highly efficient functional mimic of the photosynthetic antenna-reaction-center complexes has been designed and synthesized. The model contains a zinc(II) porphyrin (ZnP) core, which is connected to three boron dipyrromethene (BDP) units by click chemistry, and to a C(60) moiety using the Prato procedure. The compound has been characterized using various spectroscopic methods. The intramolecular photoinduced processes of this pentad have also been studied in detail with steady-state and time-resolved absorption and emission spectroscopic methods, both in polar benzonitrile and nonpolar toluene. The BDP units serve as the antennae, which upon excitation undergo singlet-singlet energy transfer to the porphyrin core. This is then followed by an efficient electron transfer to the C(60) moiety, resulting in the formation of the singlet charge-separated state (BDP)(3)-ZnP(·+) -C(60)(·-) , which has a lifetime of 476 and 1000 ps in benzonitrile and toluene, respectively. Interestingly, a slow charge-recombination process (k(CR)(t)=2.6×10(6) s(-1)) and a long-lived triplet charge-separated state (τ(CS)(T)=385 ns) were detected in polar benzonitrile by nanosecond transient measurements.

Double-decker yttrium(III) complexes with phthalocyaninato and porphyrinato ligands

A series of new yttrium(III) double-decker complexes with the same and different phthalocyaninato and porphyrinato ligands has been prepared. The homoleptic complexes Y(P)2 (P = Pc*(C7H15)8, Pc*(OC5H11)8; Pc* = 2,3,9,10,16,17,23,24-octasubstituted phthalocyaninate) have been synthesized by treating yttrium(III) acetylacetonate (Y(acac)3·H2O) with the phthalonitriles C6H2R2(CN)2 (R = C7H15, OC5H11) in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The heteroleptic analogues Y(P)(Pc) (P = Pc*(C7H15)8, Pc*(OC5H11)8; Pc = unsubstituted phthalocyaninate) and Y(P)(Por) (P = Pc, Pc*(C7H15)8; Por = meso-tetraphenylporphyrinate (TPP), meso-tetra(4-pyridyl)porphyrinate (TPyP)) have been prepared by the base-catalysed tetramerization of the corresponding phthalonitriles using Y(P)(acac) (P = Pc, TPP, TPyP) as templates. The syntheses along with the spectroscopic and electrochemical properties of these novel double-deckers are described.

SYNTHESIS AND SPECTROSCOPIC PROPERTIES OF OCTASUBSTITUTED (PHTHALOCYANINATO)TITANIUM(IV) COMPLEXES

Abstract The octasubstituted (phthalocyaninato)titanium complexes [Pc′(R)8]TiO (Pc′=2,3,9,10,16,17,23,24-octasubstituted phthalocyaninate; R=n-C7H15 (1), OC5H11 (2)) have been prepared by treating the corresponding substituted dicyanobenzenes C6H2(CN)2(R)2 with TiCl4 or Ti(OC2H5)4 in the presence of urea. Compound 1 reacts with catechol to give the catecholato complex [Pc′(C7H15)8]Ti(O2C6H4) (3). The electronic absorption spectra of 1 have been measured in a wide range of non-coordinating and coordinating solvents. The solvent effects are mainly due to solvation and the band positions depend on the polarity and coordinating power of the solvents. Aggregation has also been shown to exist for compound 1 in hexane, but not in chloroform.

Preparation of unsymmetrical distyryl BODIPY derivatives and effects of the styryl substituents on their in vitro photodynamic properties

A series of unsymmetrical distyryl BODIPYs have been prepared which function as highly potent photosensitisers with in vitro IC(50) values as low as 15 nM. Their cellular uptake, subcellular localisation and photocytotoxicity depend greatly on the styryl substituents.

A Zinc(II) Phthalocyanine Conjugated with an Oxaliplatin Derivative for Dual Chemo- and Photodynamic Therapy

A novel zinc(II) phthalocyanine substituted with an oxaliplatin derivative via a triethylene glycol linker has been synthesized. The two components work in a cooperative manner in the antitumor action. The conjugate shows a cytotoxic effect in the dark due to the cytostatic oxaliplatin moiety and an enhanced cytotoxicity upon illumination due to the photosensitizing phthalocyanine unit against the HT29 human colon adenocarcinoma cells. The IC(50) value of the conjugate is as low as 0.11 μM, which is 5-fold lower than that of the reference compound without the platinum complex. The high photodynamic activity of the conjugate can be attributed to its high cellular uptake and efficiency in generating intracellular reactive oxygen species. The conjugate also shows preferential localization in the lysosomes of the cells and induces cell death mainly through apoptosis.

A dual activatable photosensitizer toward targeted photodynamic therapy

An unsymmetrical bisferrocenyl silicon(IV) phthalocyanine has been prepared in which the disulfide and hydrazone linkers can be cleaved by dithiothreitol and acid, respectively. The separation of the ferrocenyl quenchers and the phthalocyanine core greatly enhances the fluorescence emission, singlet oxygen production, intracellular fluorescence intensity, and in vitro photocytotoxicity. The results have been compared with those for the two symmetrical analogues which contain either the disulfide or hydrazone linker and therefore can only be activated by one of these stimuli. For the dual activatable agent, the greatest enhancement can be attained under a slightly acidic environment (pH = 4.5-6.8) and in the presence of dithiothreitol (in millimolar range), which can roughly mimic the acidic and reducing environment of tumor tissues. This compound can also be activated in tumor-bearing nude mice. It exhibits an increase in fluorescence intensity in the tumor over the first 10 h after intratumoral injection and can effectively inhibit the growth of tumor upon illumination.