Desired properties of new phthalocyanines for photodynamic therapy

Abstract

The manuscript focuses on the properties of phthalocyanines (Pcs) that are required for them to be employed as photosensitizers in applications such as photodynamic therapy (PDT). High triplet-state quantum yields and lifetimes as well as high singlet-oxygen quantum yields are required for a good photosensitizer. In addition, absorption of the photosensitizer in the red region of the electromagnetic spectrum is also required, and this can be achieved by ring expansion, substitution with electron-donating ligands, and change of the central metal among others. Quantum dots (QDs) are efficient accumulators of light energy, and they can transfer this energy to molecules that possess a very efficient ability to generate singlet oxygen through a process called Förster resonance energy transfer (FRET). Thus, there is a decrease in the fluorescence quantum yield of the QDs when in the vicinity of Pcs. Triplet quantum yields of the Pcs increase in the presence of QDs.

Application of phthalocyanines in flow- and sequential-injection analysis and microfluidics systems: A review

“…Phthalocyanines (Pcs, Fig. 1) and metallophthallocyanines (MPcs) [7][8][9] play a very important role in human life since their discovery in the early nineteenth century and besides their role as colorful dye stuffs also have a wide variety of applications due to their diverse chemical, structural, electronic, and optical properties. Phthalocyanines and metallophthalocyanines are not only very useful in several innovative and emerging high technological applications like dyes, thermal writing displays, dye-sensitised photovoltaic solar cells, oxidation-, reduction-and photo-catalysis, membrane catalytic reactors, nonlinear optics and photonics, semiconductor materials, gas sensors and biosensors [10][11][12][13][14][15][16][17][18][19][20][21][22][23], but they also perform a very important role in photodynamic therapy (PDT) [7,[24][25][26][27][28][29][30][31][32][33][34][35] a novel cancer treatment that is receiving increased attention and where the group of Tobello Nyokong [7,[31][32][33][34][35] is very actively involved as a major role player.…”

“…The spectral properties of phthalocyanines (Pc's) are central to their chemical and electronic properties and are governed by the 18π system of the most inner 16-membered ring. The intense blue-green color of phthalocyanines is due to the electronic delocalization of their 18π electrons making them very useful to be utilizing industrially as dyes and pigments, catalysts and photoconductors in various fields [7,20,21,[31][32][33][42][43][44][45][46][47][48]. Dedicated specificity in many applications of phthalocyanines can be obtained by modification of the phthalocyanine ring or by changes in the central metal or axial ligands.…”

“…Dedicated specificity in many applications of phthalocyanines can be obtained by modification of the phthalocyanine ring or by changes in the central metal or axial ligands. Phthalocyanines furthermore also functions as planar tetradentate dianionic ligands that bind metals through four inwardly projecting nitrogen centers [7,32,42,44].…”

“…A change in the shape of the Q band occurs with a change in symmetry. However for highly red-shifted metallophthalocyanine complexes, the Q-band no longer determines the color [7,31]. It is well established that increasing expansion of the π-conjugation in phthalocyanines shifts the Q-band to the red [7,49].…”

“…However for highly red-shifted metallophthalocyanine complexes, the Q-band no longer determines the color [7,31]. It is well established that increasing expansion of the π-conjugation in phthalocyanines shifts the Q-band to the red [7,49]. Extension of the conjugation system is accompanied by change in color from blue/green to colors including brown, red, or purple.…”