Solid silica nanoparticles as carriers of fluorescent squaraine dyes in aqueous media: Toward a molecular engineering approach

Abstract

Hybrid squaraine-SiO2 nanoparticles extremely homogeneous in size (50±2 nm), and with photoluminescent emission in the optical tissue window, were prepare by using the reverse microemulsion technique. Three different high quantum-yield squaraine dyes were used and the photophysical behavior of the prepared samples were qualitatively and quantitatively studied, by steady state and time-resolved photoluminescence, in order to establish structure-property relationships useful for the optimization of the preparation method. These squaraine dyes are insoluble in water and suffer a severe decrease of quantum yield if derivatized with polar groups. The role of the hydrophilicity of the dye-APTS adduct in ruling its dispersion in the nascent silica matrix

Quatsomes Loaded with Squaraine Dye as an Effective Photosensitizer for Photodynamic Therapy

“…The values are nevertheless very low, probably due to the presence of some H-aggregates, as also evidenced in the UV–Vis spectra reported in Figure 3 b,c. The Br-Sq-C12 fluorescence lifetime showed a monoexponentially decay and is in the nanoseconds range, as already observed for several squaraines [ 59 ].…”

“…The UV–Vis spectrum is characterized by a narrow absorption band in the NIR, an essential requirement for the PDT treatment, and a characteristic hypsochromic shoulder typical for polymethine dyes. The main absorption peak is associated with the π→π* HOMO–LUMO transitions, mainly localized on the squaraine core; on the other hand, the shoulder at higher energy can be ascribed to the HOMO-LUMO+1 transition [ 59 , 60 ]. As already observed for other SQs [ 61 ], Br-Sq-C12 shows an excellent fluorescence emission with a maximum emission at 649 nm when dissolved in ethanol, although both the absorption and the fluorescence emission are completely quenched when dissolved in water due to an aggregation caused quenching (ACQ) effect.…”

New Two-Photon Absorbing Squaraine Derivative with Efficient Near-Infrared Fluorescence, Superluminescence, and High Photostability

“…The majority of symmetrical squaraine derivatives (with corresponding quadrupolar molecular structure: donor–acceptor–donor , ) are characterized by relatively sharp, intense long-wavelength absorption bands in the red-NIR spectral range (maximum extinction coefficient, ε max ∼ (3–4) × 10 5 M –1 cm –1 ), ,, high fluorescence quantum yields, Φ fl > 0.6, ,, and some of the highest single-molecule 2PA efficiencies (corresponding 2PA cross sections, δ 2PA max ∼ 10 4 GM). ,− The nature of these large values of δ 2PA max for symmetrical squaraines is mainly determined by the large ε max and the possibility to realize double-resonance excitation conditions . Squaraine derivatives with unsymmetrical molecular structures often exhibit much broader absorption bands with smaller values of ε max and possess significant potential for applications in organic solar cell engineering. ,, …”

“…14−16 Certain squaraine molecules exhibit high photochemical stability 17−19 and possess a wide variety of specific linear and nonlinear spectroscopic properties determined by the specific structure of the molecular architecture, including intramolecular steric factors, 4,20,21 hydrogen bonding, 22 symmetry of the electronic distribution, 19,23,24 and parameters of the terminal groups. 13,16, The majority of symmetrical squaraine derivatives (with corresponding quadrupolar molecular structure: donor− acceptor−donor 15,28 ) are characterized by relatively sharp, intense long-wavelength absorption bands in the red-NIR spectral range (maximum extinction coefficient, ε max ∼ (3−4) × 10 5 M −1 cm −1 ), 18,29,30 high fluorescence quantum yields, Φ fl > 0.6, 18,31,32 and some of the highest single-molecule 2PA efficiencies (corresponding 2PA cross sections, δ 2PA max ∼ 10 4 GM). 11,33−35 The nature of these large values of δ 2PA max for symmetrical squaraines is mainly determined by the large ε max and the possibility to realize double-resonance excitation conditions.…”

Unveiling the interaction between PDT active squaraines with ctDNA: A spectroscopic study

“…energy [8][9][10][11], biological applications [6,[12][13][14][15] and sensitizers for PDT [5,16,17]. Moreover, different studies have proved that while in dark conditions squaraines are hardly cytotoxic, after irradiation at proper wavelength, they induced a significative phototoxic activity in cancer cells, which was proportional to the squaraine concentration [5,16].…”