Photoinduced Redox Processes in Phthalocyanine Derivatives by Resonance Raman Spectroscopy

Zinc Phthalocyanine Photochemistry by Raman Imaging, Fluorescence Spectroscopy and Femtosecond Spectroscopy in Normal and Cancerous Human Colon Tissues and Single Cells

Photodynamic therapy is a clinically approved alternative method for cancer treatment in which a combination of nontoxic drugs known as photosensitizers and oxygen is used. Despite intensive investigations and encouraging results, zinc phthalocyanines (ZnPcs) have not yet been approved as photosensitizers for clinical use. Label-free Raman imaging of nonfixed and unstained normal and cancerous colon human tissues and normal human CCD18-Co and cancerous CaCo-2 cell lines, without and after adding ZnPcS4 photosensitizer, was analyzed. The biochemical composition of normal and cancerous colon tissues and colon cells without and after adding ZnPcS4 at the subcellular level was determined. Analyzing the fluorescence/Raman signals of ZnPcS4, we found that in normal human colon tissue samples, in contrast to cancerous ones, there is a lower affinity to ZnPcS4 phthalocyanine. Moreover, a higher concentration in cancerous tissue was concomitant with a blue shift of the maximum peak position specific for the photosensitizer from 691-695 nm to 689 nm. Simultaneously for both types of samples, the signal was observed in the monomer region, confirming the excellent properties of ZnPcS4 for photo therapy (PDT). For colon cell experiments with a lower concentration of ZnPcS4 photosensitizer, c = 1 × 10-6 M, the phthalocyanine was localized in mitochondria/lipid structures; for a higher concentration, c = 9 × 10-6 M, localization inside the nucleus was predominant. Based on time-resolved experiments, we found that ZnPcS4 in the presence of biological interfaces features longer excited-state lifetime photosensitizers compared to the aqueous solution and bare ZnPcS4 film on CaF2 substrate, which is beneficial for application in PDT.

Fluorescent H-aggregates of an asymmetrically substituted mono-amino Zn(ii) phthalocyanine

The photophysical properties of a newly synthesized unsymmetrically substituted zinc phthalocyanine derivative (1) bearing in its peripheral positions six n-hexylsulfanyl substituents and one amino-terminated n-hexylsulfanyl substituent were investigated. This mono-amino phthalocyanine exhibited a high tendency to form H-type aggregates in all of the investigated solvents: dichloromethane (DCM), tetrahydrofuran (THF) and dimethyl sulfoxide (DMSO). Several species of H-aggregates were present together in relatively broad concentration ranges in THF and DCM, whereas in DMSO they were observed separately depending on the concentration used. Despite the widely accepted non-emissive character of H-type dimers, the H-type aggregates of phthalocyanine 1 were highly emissive in all solvents: the fluorescence quantum yield in DMSO for the n-aggregate is equal to 0.05, whereas for the (n + 1)-aggregate it is 0.11. Upon (n + 1)-aggregation, the fluorescence lifetime of the n-aggregate increased from ca. 2.5 ns to 3.3 ns. Based on these results, the radiative lifetimes of both species were computed: 48 ns for the n-aggregate and 29 ns for the (n + 1)-aggregate. The determined oscillator strengths for the n-aggregate and the (n + 1)-aggregate in DMSO were 0.04 and 0.12, respectively. The observed emission of the H-type (n + 1)-aggregate was assigned to the radiative transition from the upper exciton state to the ground state, which could be rationalized by a constant thermal repopulation of the upper exciton state. The experimental findings were supported by theoretical calculations.

Efficient On-Off Ratiometric Fluorescence Probe for Cyanide Ion Based on Perturbation of the Interaction between Gold Nanoclusters and a Copper(II)-Phthalocyanine Complex

A new ratiometric fluorescent sensor was developed for the sensitive and selective detection of cyanide ion (CN(-)) in aqueous media. The ratiometric sensing system is based on CN(-) modulated recovery of copper(II) phthalocyanine (Cu(PcTs)) fluorescence signal at the expense of diminished fluorescence intensity of gold nanoclusters (AuNCs). Preliminary experiments revealed that the AuNCs and Cu(PcTs) possess a turn-off effect on each other, the interaction of which being verified through studying their interactions by principle component analysis (PCA) and multivariate cure resolution-alternating least-squares (MCR-ALS) methods. In the presence of CN(-) anion, the AuNCs and Cu(PcTs) interaction was perturbed, so that the fluorescence of Cu (PcTs), already quenched by AuNCs, was found to be efficiently recovered, while the fluorescence intensity of AuNCs was quenched via the formation of a stable [Au(CN)2](-) species. The ratiometric variation of AuNCs and Cu(PcTs) fluorescence intensities leads to designing a highly sensitive probe for CN(-) ion detection. Under the optimal conditions, CN(-) anion was detected without needing any etching time, over the concentration range of 100 nM-220 μM, with a detection limit of 75 nM, which is much lower than the allowable level of CN(-) in water permitted by the World Health Organization (WHO). Moreover, the detection of CN(-) was developed based on the CN(-) effects on the blue and red florescent colors of Cu(PcTs) and AuNCs, respectively. The designed probe displays a continuous color change from red to blue by addition of CN(-), which can be clearly observed by the naked eye in the range of 7-350 μM, under UV lamp. The prepared AuNCs/Cu(PcTs) probe was successfully utilized for the selective and sensitive determination of CN(-) anion in two different types of natural water (Rodbal dam and rainwater) and also in blood serum as a biological sample.

Protonation of some non-transition metal phthalocyanines — spectral and photophysicochemical consequences

The photophysics and photochemistry of phthalocyanine complexes of magnesium (MgPc), aluminum chloride (ClAlPc) and zinc (ZnPc) are studied in N,N′-dimethylformamide (DMF). The values obtained for the photophysical and photochemical parameters are normal for simple metallophthalocyanine (MPc) complexes. Protonation of the azomethine bridges reduced the photoactivities of the complexes considerably; however the excited triplet states of the protonated species are more stable towards ground state oxygen. The interaction of the non-protonated MPcs with ground state oxygen is shown to be diffusion-assisted, with bimolecular rate constant values of the order of 1010 M-1.s-1. MgPc could not be protonated; it was easily demetalated by the protonating acid. The kinetics of the demetalation yielded the rate equation: Rate = 0.1[MgPc][H+]2/3

Distribution of phthalocyanines and Raman reporters in human cancerous and noncancerous breast tissue as studied by Raman imaging

There is a considerable interest in the developing new diagnostic techniques allowing noninvasive tracking of the progress of therapies used to treat a cancer. Raman imaging of distribution of phthalocyanine photosensitizers may open new possibilities of Photodynamic Therapy (PDT) to treat a wide range of neoplastic lesions with improved effectiveness of treatment through precise identification of malignant areas. We have employed Raman imaging and Raman spectroscopy to analyze human breast cancer tissue that interacts with photosensitizers used in the photodynamic therapy of cancer. PCA (Principal Component Analysis) has been employed to analyze various areas of the noncancerous and cancerous breast tissues. The results show that the emission spectra combined with the Raman images are very sensitive indicators to specify the aggregation state and the distribution of phthalocyanines in the cancerous and noncancerous breast tissues. Our results provide experimental evidence on the role of aggregation of phthalocyanines as a factor of particular significance in differentiation of the normal and tumourous (cancerous or benign pathology) breast tissues. We conclude that the Raman imaging reported here has a potential to be a novel and effective photodynamic therapeutic method with improved selectivity for the treatment of breast cancer.

Ultrafast dynamics of metal complexes of tetrasulphonated phthalocyanines

A promising material in medicine, electronics, optoelectronics, electrochemistry, catalysis, and photophysics, tetrasulphonated aluminum phthalocyanine (AlPcS(4)), is investigated by means of steady-state and time-resolved pump-probe spectroscopies. Absorption and steady-state fluorescence spectroscopy indicate that AlPcS(4) is essentially monomeric. Spectrally resolved pump-probe data are recorded on time scales ranging from femtoseconds to nanoseconds. The nature of these fast processes and pathways of the competing relaxation processes from the initially excited electronic states in aqueous and organic (dimethyl sulfoxide) solutions are discussed. The decays and bleaching recovery have been fitted in the ultrafast window (0-10 ps) and later time window extending to nanoseconds (0-1 ns). While the excited-state dynamics have been found to be sensitive to the solvent environment, we were able to show that the fast dynamics is described by three time constants in the ranges of 115-500 fs, 2-25 ps, and 150-500 ps. We were able to ascribe these three time constants to different processes. The shortest time constants have been assigned to vibrational wavepacket dynamics. The few picosecond components have been assigned to vibrational relaxation in the excited electronic states. Finally, the 150-500 ps components represent the decay from S(1) to the ground state. The experimental and theoretical treatment proposed in this paper provides a basis for a substantial revision of the commonly accepted interpretation of the Soret transition (B transition) that exists in the literature.

Excited State Dynamics and Nonlinear Absorption of a Pyrazinoporphyrazine Macrocycle Carrying Externally Appended Pyridine Rings

The multiphoton absorption properties of the tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato(monoacquo)-Mg(II) complex [Py(8)TPyzPzMg(H(2)O)] (1) are reported and interpreted. The nonlinear optical behavior of 1 and the characterization of the excited states important for the nonlinear absorption process were studied at the pump frequency of the second harmonic generation of a Nd:YAG laser in the nanosecond time regime. It was found that complex 1 shows a very good optical limiting performance at 532 nm, which derives from two processes: (a) a reverse-saturable absorption process, which involves a triplet excited state at low intensities, and (b) a two-photon absorption process at higher intensities, which is due to the formation of the radical monoanion of 1, [Py(8)TPyzPzMg(H2O)](.-), during the photoreduction of the triplet state. The participation of a monoanion in determining the overall nonlinear absorption behavior of 1 is found, for the first time, for a tetrapyrrolic system. One can deduce that the involvement of the monoanion derives from the electron-withdrawing effect of the dipyridinopyrazino fragments externally attached to the porphyrazine core which make the reduced form of 1 easily accessible. These results suggest a modification of tetrapyrrolic systems with new nonlinear absorption properties.

Femtosecond Transient Absorption, Raman, and Electrochemistry Studies of Tetrasulfonated Copper Phthalocyanine in Water Solutions

Ultrafast time-resolved electronic spectra of the primary events induced in the copper tetrasulfonated phthalocyanine Cu(tsPc)4-) in aqueous solution has been measured by femtosecond pump-probe transient absorption spectroscopy. The primary events initiated by the absorption of a photon occurring within the femtosecond time scale are discussed on the basis of the electron transfer mechanism between the adjacent phthalocyanine rings proposed recently in our laboratory. The femtosecond transient absorption results are compared with the low temperature emission spectra obtained with Raman spectroscopy and the voltammetric curves.