Morpholine-Phthalocyanine (Donor–Acceptor) Construct: Photoinduced Intramolecular Electron Transfer and Triplet Formation from its Charge Separation State

Molecular torsion controls the excited state relaxation pathways of multibranched tetraphenylpyrazines: effect of substitution of morpholine vs. phenoxazine

Multibranched donor-acceptor derivatives exhibiting desirable photophysical properties are efficiently used in optoelectronic devices, in which the excited state relaxation dynamics of the derivatives control the efficiency of the devices. Here, the effect of intramolecular torsion on the excited state relaxation dynamics of tetraphenylpyrazine (TPP) derivatives in non-polar (toluene) and polar (THF) solvents is investigated by substituting the electron donor of morpholine (TPP-4MOP) and phenoxazine (TPP-4PHO) leading to the planar and twisted configurations, respectively, using femtosecond and nanosecond transient absorption spectroscopy. In the steady state, TPP-4MOP showed feeble emission (ΦF ∼0.03) due to the weak donor by the delocalization of electron density supported by theoretical optimization. The TPP-4PHO exhibited strong emission (ΦF ∼0.18) in toluene compared to that in THF, in which it showed a large Stokes shift (∼9691 cm-1) with low fluorescence quantum yield (ΦF ∼0.01). The observation of large Stokes shifts, inherent nature and theoretical calculations of TPP-4PHO suggest the twisting of the dihedral angle between tetraphenylpyrazine and phenoxazine in the excited state leading to the twisted intramolecular charge transfer state (TICT). The femtosecond and nanosecond transient absorption and picosecond time-resolved emission spectra of TPP-4PHO revealed the signature of the existence of both the partial TICT and TICT states in THF leading to the triplet state. Whereas in the case of TPP-4MOP, the transient absorption spectra showed the formation of the triplet state from the local excited state without the involvement of the TICT state. Aggregation studies of TPP-4PHO in a THF and water mixture reflect the elimination of the TICT state by the restriction of intramolecular torsion in the aggregates leading to an increase of 12-fold of the fluorescence intensity along with shifting of the maximum towards the blue region. These studies revealed that the excited state relaxation pathways of the derivatives are controlled by polarity-dependent torsional motion.

Morpholinyl silicon phthalocyanine nanoparticles with lysosome cell death and two-photon imaging functions for in vitro photodynamic therapy of cancer cells

The lysosome is an important target for realizing antitumor therapy. Lysosomal cell death exerts significant therapeutic effects on apoptosis and drug-resistance. The development of lysosome-targeting nanoparticles to obtain efficient cancer treatment is challenging. In this article, nanoparticles composed of DSPE@M-SiPc and possessing bright two-photon fluorescence, lysosome targeting ability, and photodynamic therapy multifunctionalities are prepared by encapsulating morpholinyl-substituted silicon phthalocyanine (M-SiPc) with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(poly(ethylene glycol))-2000] (DSPE). Two photon fluorescence bioimaging showed that M-SiPc and DSPE@M-SiPc mainly locate in lysosomes after cellular internalization. Upon irradiation, DSPE@M-SiPc effectively generates reactive oxygen species and damages the function of lysosome, subsequently leading to lysosomal cell death. DSPE@M-SiPc is a promising photosensitizer for cancer treatment.

The excited state behavior of Group IA alkaline-metal phthalocyanines revealed by photoluminescence and singlet oxygen formation

Group IA alkaline-metal phthalocyanine (Pc) complexes (Li₂Pc, Na₂Pc, K₂Pc, Rb₂Pc, Cs₂Pc) have been synthesized and purified to study their excited state behavior. Their UV-Vis electronic absorption spectra, fluorescence emission and excitation spectra, fluorescence quantum yields and lifetimes, as well as singlet oxygen formation quantum yields have been measured in DMF. These photophysical properties are compared with that of H₂Pc. The fluorescence and singlet oxygen formation properties reveal that alkaline metal Pcs show weak heavy atom effect. The results also reveal that alkaline-metal Pcs (Na₂Pc, K₂Pc, Rb₂Pc, and Cs₂Pc) show very different excited singlet state (S₁) behavior from that of Li₂PC and H₂Pc. While S₁ decay of Li₂PC is mainly via intersystem crossing and fluorescence, the S₁ decay of M₂Pc (M = Na, K, Rb, Cs) is mainly metal ion dissociation: M₂Pc(S₁) → 2 M⁺ + [Pc]^2-(S₁), in addition to the intersystem crossing.

The use of new metallophthalocyanines carrying peripherally 4-methyl-N-(3-morpholinopropyl)benzenesulfonamide moieties for the sensitive fluorimetric determination of banned food dye Sudan II in red chili peppers

The structural elucidation and syntheses methods of new peripherally tetra-substituted MPcs [CuII(6), CoII(7), MnCIIII(8), and NiII(9) phthalocyanines] carrying 4-methyl-N-(3-morpholinopropyl)benzenesulfonamide moieties were reported in the present study. The corroboration of the prepared compounds (3, 5, and 6 to 9) was made by LC-TOF/MS, UV-Vis, Fourier Infrared, 1H NMR, 13C NMR, and MALDI-TOF mass spectral data. Herein, we submit a new procedure that uses metallophthalocyanine complexes for the first time as spectrofluorimetric agents to detect and determine health-threatening food additive, Sudan II dye, with a new simpler, cheaper, and faster spectrofluorimetric method instead of time-consuming and expensive HPLC processes. Furthermore, the sensitivities of the proposed methods are good enough to determine the amount of dye at a concentration of 0.1 mg/L. The methods have LOD values between 0.035 and 0.050 mg/L. The linear ranges are found to be between 0 and 8.3 mg/L. The precision of the methods is determined to be between 1.1 and 2.4 as % RSD. Therefore, this study would make a good contribution to the food industry and phthalocyanine chemistry by detecting and determining the hazardous food colorant Sudan II with metal phthalocyanines.

Third-order nonlinear optical properties of axially modified indium phthalocyanines with alkyl chains

Novel axially substituted indium phthalocyanine with strong NLO properties: effects of the length of the alkyl chain.

Defining the conditional basis of silicon phthalocyanine near-IR ligand exchange

Bond cleavage reactions initiated by long-wavelength light are needed to extend the scope of the caged-uncaged paradigm into complex physiological settings. Axially unsymmetrical silicon phthalocyanines (SiPcs) undergo efficient release of phenol ligands in a reaction contingent on three factors - near-IR light (690 nm), hypoxia, and a thiol reductant. These studies detail efforts to define the mechanistic basis for this unique conditionally-dependent bond cleavage reaction. Spectroscopic studies provide evidence for the formation of a key phthalocyanine radical anion intermediate formed from the triplet state in a reductant-dependent manner. Computational chemistry studies indicate that phenol ligand solvolysis proceeds through a heptacoordinate silicon transition state and that this solvolytic process is favored following SiPc radical anion formation. These results provide insight regarding the central role that radical anion intermediates formed through photoinduced electron transfer with biological reductants can play in long-wavelength uncaging reactions.

Morpholinyl dendrimer phthalocyanine: synthesis, photophysical properties and photoinduced intramolecular electron transfer

The photophysical properties of a novel series of morpholinyl dendrimer phthalocyanines exhibited dependence on the number of morpholinyl groups and the central ion. The photoinduced electron transfer from the morpholinyl units to phthalocyanine ring was evidenced.

Ethylenediamine-modified graphene oxide covalently functionalized with a tetracarboxylic Zn(ii) phthalocyanine hybrid for enhanced nonlinear optical properties

Tetracarboxylic Zn(ii) phthalocyanine-amino functionalized graphene oxide (ZnPcC4-NGO) hybrid materials have been prepared by a covalent functionalization method. The characterizations indicate that the amino-functionalization of GO has an important influence on the structure and photophysical properties of the ZnPcC4-NGO hybrid. The ZnPcC4-NGO hybrid exhibits enhanced photo-induced electron transfer or energy transfer (PET/ET), compared to the ZnPcC4 covalent functionalized GO (ZnPcC4-GO), owing to the presence of the extended sp(2) carbon configurations, along with the partial reduction of the NGO nanosheets and the introduction of electron-donating ethylenediamine. The nonlinear optical (NLO) properties of the hybrids were investigated using the Z-scan technique at 532 nm with 4 ns laser pulses. The results show that the efficient covalent functionalization and partial reduction of NGO cause the ZnPcC4-NGO hybrid to possess evidently larger NLO properties than the individual NGO, ZnPcC4 and the ZnPcC4-GO hybrid. The enhanced NLO performance can be attributed to the increased excited state absorption from the extended sp(2) carbon configurations of the NGO moiety, reverse saturable absorption arising from ZnPcC4 moiety, and the contribution of the efficient PET/ET process between the ZnPcC4 and NGO moieties in the hybrid.

Near-infrared uncaging or photosensitizing dictated by oxygen tension

Existing strategies that use tissue-penetrant near-infrared light for the targeted treatment of cancer typically rely on the local generation of reactive oxygen species. This approach can be impeded by hypoxia, which frequently occurs in tumour microenvironments. Here we demonstrate that axially unsymmetrical silicon phthalocyanines uncage small molecules preferentially in a low-oxygen environment, while efficiently generating reactive oxygen species in normoxic conditions. Mechanistic studies of the uncaging reaction implicate a photoredox pathway involving photoinduced electron transfer to generate a key radical anion intermediate. Cellular studies demonstrate that the biological mechanism of action is O₂-dependent, with reactive oxygen species-mediated phototoxicity in normoxic conditions and small molecule uncaging in hypoxia. These studies provide a near-infrared light-targeted treatment strategy with the potential to address the complex tumour landscape through two distinct mechanisms that vary in response to the local O₂ environment.

Photo-induced electron transfer in a diamino-substituted Ru(bpy)3[PF6]2 complex and its application as a triplet photosensitizer for nitric oxide (NO)-activated triplet–triplet annihilation upconversion

The photo-induced electron transfer in the diamino-Ru(bpy)₃ complex was studied with ultrafast absorption spectroscopy and was used for nitric oxide (NO)-activated triplet–triplet annihilation upconversion.

Photophysics of silicon phthalocyanines in aqueous media

Phthalocyanines have been used as photodynamic therapy (PDT) agents because of their uniquely favorable optical properties and high photostability. They have been shown to be highly successful for the treatment of cancer through efficient singlet-oxygen ((1)O(2)) production. However, due to their hydrophobic properties, the considerations of solubility and cellular location have made understanding their photophysics in vitro and in vivo difficult. Indeed, many quantitative assessments of PDT reagents are undertaken in purely organic solvents, presenting challenges for interpreting observations during practical application in vivo. With steady-state and time-resolved laser spectroscopy, we show that for axial ligated silicon phthalocyanines in aqueous media, both the water:lipophile ratio and the pH have drastic effects on their photophysics, and ultimately dictate their functionality as PDT drugs. We suggest that considering the presented photophysics for PDT drugs in aqueous solutions leads to guidelines for a next generation of even more potent PDT agents.

Modulating the singlet oxygen generation property of meso-β directly linked BODIPY dimers

We report the synthesis, X-ray analysis and singlet oxygen generation properties of a set of meso-β directly linked BODIPYs with the meso-aryl group (φ(1)) and meso-BODIPY component (φ(2)) free to rotate or constrained.