Quantum Yield Of Radicals Research Articles

Assessing excimer far-UVC (222 nm) irradiation for advanced oxidation processes: Oxidants photochemistry and micropollutants degradation

The KrCl* excimer lamp (UV222) is a promising alternative of low-pressure mercury lamp (UV254) for UV-based advanced oxidation processes (UV-AOPs), because it is mercury-free and has high photon energy. But there lacks a comprehensive assessment of UV222-AOPs based on different radicals. Herein, the properties (e.g., oxidant decay and innate radical quantum yield), and micropollutant degradation, were comprehensively studied for representative oxidants (i.e., hydrogen peroxide, persulfate (PDS), monochloramine, and free active chlorine (FAC)) under UV222 irradiation. UV222 outperformed UV254 for the activation of oxidants with 2.6–14.4 times fluence-based kinetic constant (kF). The main reason of enhanced activation varied with oxidants: higher UV absorbance for H2O2, higher innate quantum yield for monochloramine and FAC, and both reasons for PDS. Overall, PDS was the optimum oxidant under UV222 for the degradation of 8 representative micropollutants because of effective promotion of radical formation, as confirmed by radical competitive kinetics and modeling simulations. In real water, UV222/PDS still show advantages than UV254/PDS in terms of micropollutant elimination efficacy (3.2–5.3 times) and energy consumption (33.9 %-57.6 % lower) though it was more inhibited by water constituents via competing for UV222 photons. This study fills gaps in photochemistry knowledge and will facilitate engineering practice of UV222-AOPs.

Fast and efficient synthesis of polymers driven by solar radiation. New insights on dye/dendrimer photoinitiating systems

The performance of a series of visible-light driven photoinitiating systems (Vis-PIs) for radical polymerization was evaluated. The Vis-PIs formulations consisted of aqueous solutions containing xanthene dyes as sensitizers, while polyamido-amine (PAMAM) dendrimers were tested as alternative co-initiators of lower toxicity than the traditional amines. Acrylamide and HEMA were used as probe monomers and the respective polymers were characterized by FTIR, DSC and viscosimmetry. In order to elucidate the mechanism of photopolymerization, the triplet excited-states and semirreduced forms of the dyes were characterized by transient spectroscopy. Photophysical parameters as intersystem crossing and radical quantum yields were also determined for each dye/dendrimer couple. All Vis-PIs operated successfully under solar irradiation, achieving high monomer conversions after short exposure times. Interestingly, formulations with partially halogenated dyes showed the highest efficiency, which correlates inversely with the affinity and the electron transfer capability between the reactants. This study demonstrates the usefulness of dye/dendrimer combinations to operate as efficient aqueous Vis-PIs under an inexpensive, unlimited and natural energy source such as sunlight.

Direct Determination of Absolute Radical Quantum Yields in Hydroxyl and Sulfate Radical-Based Treatment Processes.

The absolute radical quantum yield () is a critical parameter to evaluate the efficiency of radical-based processes in engineered water treatment. However, measuring is fraught with challenges, as current quantification methods lack selectivity, specificity, and anti-interference capabilities, resulting in significant error propagation. Herein, we report a direct and reliable time-resolved technique to determine at pH 7.0 for commonly used radical precursors in advanced oxidation processes. For H2O2 and peroxydisulfate (PDS), the values of •OH and at 266 nm were measured to be 1.10 ± 0.01 and 1.46 ± 0.05, respectively. For peroxymonosulfate (PMS), we developed a new approach to determine with terephthalic acid as a trap-and-trigger probe in the nonsteady state system. For the first time, the value was measured to be 0.56 by the direct method, which is stoichiometrically equal to (0.57 ± 0.02). Additionally, radical formation mechanisms were elucidated by density functional theory (DFT) calculations. The theoretical results showed that the highest occupied molecular orbitals of the radical precursors are O-O antibonding orbitals, facilitating the destabilization of the peroxy bond for radical formation. Electronic structures of these precursors were compared, aiming to rationalize the tendency of the values we observed. Overall, this time-resolved technique with specific probes can be used as a reliable tool to determine , serving as a scientific basis for the accurate performance evaluation of diverse radical-based treatment processes.

Covalent Organic Framework Nanocages with Enhanced Carrier Utilization and Cavitation Effect for Cancer Sonodynamic Therapy.

Ultrasound (US)-triggered sonodynamic therapy (SDT) is an emerging method for treating cancer due to its non-invasive nature and high-depth tissue penetration ability. However, current sonosensitizers commonly have unsatisfactory quantum yields of free radicals. In this work, we have developed unique organic semiconductor π-conjugated covalent organic framework nanocages (COFNs) as highly efficient sonosensitizers to boost free radical (1O2 and •OH) production and cancer therapy. With the hollow and porous structure and band transport behavior, COFNs displayed remarkably improved SDT performance through enhanced electron utilization and cavitation effect, with a 1.8-fold increase in US pressure and a 64.8% increase in 1O2 production relative to the core-shell-structured COF under US irradiation. The in vitro and in vivo experimental results verified the elevated SDT performance, showing a high tumor suppression of 91.4% against refractory breast cancer in mice. This work provides a promising strategy to develop high-performance sonosensitizers for cancer therapy.

Photolysis of Fe(III) complex with ethylenediamine-N,N′-disuccinic acid and its efficiency in generation of •OH radical

The mechanism of photolysis of the Fe(III) complex with ethylenediamine-N,N′-disuccinic acid ([FeEDDS]-) was revealed using a combination of time resolved and stationary photochemical methods. Using laser flash photolysis (λex = 355 nm), the formation of the primary intermediate, the radical complex of Fe(II) with quantum yield (φ0 = 0.21) was detected for the first time. The lifetime (1.8 ms) and the spectral characteristics (λmax = 520 nm, ε520 nm = 160 M−1cm−1) of this intermediate were also determined. The dependence of the quantum yield of photolysis of the [FeEDDS]- complex (φFeEDDS) and the hydroxyl radical quantum yield (φOH) on the excitation wavelength, pH, and concentrations of the ligand and iron ions were obtained for the first time. It has been established that under optimal conditions at neutral pH, the value of φFeEDDS is about 0.8, and φOH is about 0.15. It was found that φFeEDDS does not depend on the initial concentrations of Fe(III), EDDS, but depends on pH, the excitation wavelength and the presence of oxygen. φOH does not depend on the initial concentrations of Fe(III), EDDS, but depends on pH and the excitation wavelength. The high φOH values make the [FeEDDS]- complex a suitable system for the generation of •OH radical at neutral pH under UV radiation.

Integrated evaluation of the reactive oxygen species (ROS) production characteristics in one large lake under alternating flood and drought conditions

Reactive oxygen species (ROS) are omnipresent in natural aquatic environments, and play an important role in biogeochemical cycles. One of the dominant sources of ROS in surface waters was thought to be from dissolved organic matter (DOM) interacting with photochemical process. The properties of DOM were different between the flood and drought periods in lakes; yet, information on how these variations influence ROS photoproduction is unknown. Through a three-year study, the photochemical properties of DOM and the resultant ROS photoproduction between the flood and drought period were determined in the largest freshwater lake in China (Lake Poyang). Results found that quantum yield coefficients of excited triplets (3CDOM*), apparent quantum yields of singlet oxygen (1O2) and hydroxyl radicals (•OH) were holistically higher in the flood period than those in the drought period. The optical properties of DOM showed that DOM in the flood period featured an allochthonous input, accompanied by higher molecular size (E2/E3), aromatic content (SUVA254), humification degree (HIX), while DOM in the drought period was mainly internal input. Fourier transform ion cyclotron resonance mass spectrometry (FI-ICR MS) further revealed that some refractory components, such as lignin-like and carboxyl-rich alicyclic molecules (CRAM) presented higher abundance in the flood period, and played the positive impacts on ROS production. Orthogonal partial least squares (OPLS) were used to build novel multivariate predictive models for indicating the spatio-temporal ROS production. Also, the relatively higher steady-state concentrations of 3CDOM* and 1O2 in the flood period could significantly diminish the half-lives of acetochlor. Considering the photochemical activity of DOM varied considerably at different periods, this study provided a new method to predict ROS production and contributed to a new insight into stage-specific emerging contaminants removing in natural aquatic environments.

Remote effect of substituents on the properties of phenyl thienyl thioether-based oxime esters as LED-sensitive photoinitiators

Visible light-sensitive photoinitiators (PIs) are essential for light-emitting diode (LED) photopolymerization as LEDs are becoming the predominant light sources. In this work, five phenyl thienyl thioether-based oxime esters with different electron-donating and -withdrawing substituents on the para-position of the phenyl ring were designed and synthesized as LED-sensitive PIs. These oxime esters exhibited a maximum absorption band matched with the LED emission spectra (e.g., 365–425 nm). The remote substituents clearly affected the absorption of the oxime esters, and the principle was investigated via DFT calculations. The substituents also enhanced the initiation activities with the increase in the quantum yields of photo-induced free radical generation. Besides, upon comparison of the quantum yields of fluorescence, photolysis, and free radicals, a fast intersystem crossing was proposed for the excited states of these oxime esters, and results revealed the photoreactions were mainly from the triplet states. Finally, photo-DSC was employed to evaluate the actual photopolymerization. Results suggested that they could all efficiently initiate the free radical polymerization of acrylates under LED irradiation, making them suitable PIs for LED polymerization. This study could provide some significance to the design of PIs with improved efficiency.

Raman and Quantum Yield Studies of Trp48-d5 in Azurin: Closed-Shell and Neutral Radical Species.

Isotopologues are valuable vibrational probes that shift features in a vibrational spectrum while preserving the electronic structure of the molecule. We report the vibrational and electronic spectra of perdeuterated tryptophan in solution (l-Trp-d5), as Trp48-d5 in azurin, and as the photogenerated neutral tryptophan radical, Trp48-d5•, in azurin. The UV resonance Raman bands of the perdeuterated closed-shell tryptophan in solution and in azurin are lower in frequency relative to the protiated counterpart. The observed decrease in frequencies of l-Trp-d5 bands relative to l-Trp-h5 enables the analysis of vibrational markers of other amino acids, e.g., phenylalanine, that overlap with some modes of l-Trp-h5. The Raman intensities vary between l-Trp-d5 and l-Trp-h5; these differences likely reflect modifications in normal mode composition upon perdeuteration. Analysis of the W3, W6, and W17 modes suggests that the W3 mode retains its utility as a conformational marker; however, the H-bond markers W6 and W17 appear to be less sensitive upon perdeuteration. The neutral tryptophan radical, Trp48-d5•, was generated in azurin with a slightly lower radical quantum yield than for Trp48-h5•. The visible resonance Raman spectrum of Trp48-d5• is different from that of Trp48-h5•, especially in terms of relative intensities, and all assignable peaks decreased in frequency upon perdeuteration. The absorption and emission spectra of the perdeuterated closed-shell and radical species exhibited hypsochromic shifts of less than 1 nm relative to the protiated species. The data presented here indicate that l-Trp-d5 is a valuable probe of vibrational structure, with minimal modification of photoreactivity and photophysics compared to l-Trp-h5.

Effects of Electromagnetic Fields on the Quantum Yield of Free Radicals in Cryptochrome

In this paper, the effects of the quantum yield of free radicals in cryptochrome exposed to different electromagnetic fields were studied through the quantum biology. The results showed that the spikes characteristics was produced in the free radicals in cryptochrome, when it exposed to the applied magnetic field (ω = 50 Hz, B0 = 50 μT). The spikes produced by the electromagnetic field was independent of the changes of polar θ. When the frequency of the magnetic field increased, the spikes characteristics produced in unit time also increased. These results showed that the environmental electromagnetic field could affect the response of organisms to the geomagnetic field by influencing the quantum yield in the mechanism of free radical pair.It provided a basis for studying the influence of environmental electromagnetic field on biology, especially the navigation of biological magnetism.

Degradation of metronidazole by UV/chlorine treatment: Efficiency, mechanism, pathways and DBPs formation

Metronidazole (MET) is a widely used antibiotic but is recalcitrant in aquatic environment. This study investigated elimination of MET by UV/chlorine process systematically. The degradation of MET in the process well fitted pseudo first-order kinetics. Decreasing pH from 9 to 5 raised the rate constant from 0.0199 min-1 to 0.1485 min-1, possibly ascribed to change in species distribution and apparent quantum yields of radicals. Scavenging experiments indicated that both HO and Cl contributed to the degradation of MET, and that HO was the dominant species in the pH range studied. The second-order rate constant between Cl and MET was determined to be (5.64 ± 0.1) × 109 M-1 s-1. Three products were identified by UPLC-Q-TOF MS and degradation pathway was thus proposed. Significant amounts of chlorinated disinfection by-products (DBPs) were produced and 1,1,1-TCP was the dominant (83.6%-92.3%) in the UV/chlorine process. The kinetic model developed fitted well with experimental results, and was used to examine the effects of typical water parameters, such as chorine dosage, pH, inorganic anions, NOM and real water matrix. Furthermore, removal efficiency of MET by the UV/chlorine process were assessed in terms of electrical energy per order (EE/O). The efficiency was about 0.43 kWh m-3 order-1, 0.54 kWh m-3 order-1, 0.57 kWh m-3 order-1, respectively, for the removal of MET in ultrapure water (UPW) and two types of real water samples, indicating that UV/chorine was a practical method for authentic drinking water treatment practices.

Hydroxyl Radical Fluorescence and Quantum Yield Following Lyman-α Photoexcitation of Water Vapor in a Room Temperature Cell and Cooled in a Supersonic Expansion.

Photoexcitation of water by Lyman-α (121.6 nm) induces a dissociation reaction that produces OH(A2Σ+) + H. Despite this reaction being part of numerous studies, a combined understanding of the product and fluorescence yields is still lacking. Here, the rotational and vibrational distributions of OH(A) are determined from dispersed fluorescence following photoexcitation of both room-temperature and jet-cooled water vapor, for the first time in the same experiment. This work compares new data of state-resolved fluorescence with literature molecular branching ratios and brings previous studies into agreement through careful consideration of OH(A) fluorescent and predissociation lifetimes and confirms a fluorescent quantum yield of 8%. Comparison of the room-temperature and jet-cooled OH(A) populations indicate the temperature of H2O prior to excitation has subtle effects on the OH(A) population distribution, such as altering the rotational distribution in the ν' = 0 population and affecting the population in the ν' = 1 state. These results indicate jet-cooled water vapor may have a 1% higher fluorescence quantum yield compared to room-temperature water vapor.

A Comparative Study on the Photophysics and Photochemistry of Xanthene Dyes in the Presence of Polyamidoamine (PAMAM) Dendrimers

The photophysical and photochemical properties of the xanthene dyes Eosin Y, Erythrosin B, and Rose Bengal are evaluated in the presence of amino-terminated polyamidoamine (PAMAM) dendrimers of relatively high generation (G3-G5) in alkaline aqueous solution. UV/Vis absorption and fluorescence spectra of the dyes show bathochromic shifts, which correlate with the size of the dendrimer. Binding constants (Kbind ) are calculated from absorption data. The resulting high Kbind values indicate strong interactions between both molecules. Triplet-triplet absorption spectra of the dyes are recorded by laser flash photolysis, and a decrease in the triplet lifetimes is observed in the presence of dendrimers. At the same time, an increase in the absorption of the semireduced form of the dyes is observed. Rate constants for triplet quenching (3 kq ) and radical quantum yields (ΦR ) are obtained. The results are explained by a very efficient electron-transfer process from PAMAM to xanthene dyes for all of the dye/dendrimer couples that are evaluated.

Degradation of polyvinyl alcohol (PVA) by UV/chlorine oxidation: Radical roles, influencing factors, and degradation pathway

Polyvinyl alcohol (PVA) is widely used in industry but is difficult to degrade. In this study, the synergistic effect of UV irradiation and chlorination on degradation of PVA was investigated. UV irradiation or chlorination alone did not degrade PVA. By contrast, UV/chlorine oxidation showed good efficiency for PVA degradation via generation of active free radicals, such as OH and Cl. The relative importance of these two free radicals in the oxidation process was evaluated, and it was shown that OH contributed more to PVA degradation than Cl did. The degradation of PVA followed pseudo first order kinetics. The rate constant k increased linearly from 0 min−1 to 0.3 min−1 with increasing chlorine dosage in range of 0 mg/L to 20 mg/L. However, when the chlorine dosage was increased above 20 mg/L, scavenging effect of free radicals occurred, and the degradation efficiency of PVA did not increase much more. Acidic media increased the degradation efficiency of PVA by UV/chlorine oxidation more than basic or neutral media because of the higher ratio of [HOCl]/[OCl−], higher free radical quantum yields, and the lower free radical quenching effect under acidic conditions. Results of Fourier Transform Infrared Spectroscopy showed that carbonyl groups in degradation products were formed during UV/chlorine oxidation, and a possible degradation pathway via alcohol to carbonyl was proposed.

Degradation kinetics and mechanism of desethyl-atrazine and desisopropyl-atrazine in water with [rad]OH and SO4[rad]− based-AOPs

Desethyl-atrazine (DEA) and desisopropyl-atrazine (DIA) are the two major degradation by-products of atrazine (a suspected human carcinogen and endocrine disrupting herbicide), and show an equal toxicity to their parent compound. This study investigated the degradation of DEA and DIA with OH and SO4− generated from the activation of peroxides, i.e., persulfate (S2O82−), peroxymonosulfate (HSO5−) and hydrogen peroxide (H2O2), by UV-254nm radiation in the presence or absence of Fe2+. Quantum yields of DEA and DIA were independent of pH (3.0–11.0). The higher quantum yield of reactive radicals from UV/S2O82−, i.e., 1.8 compared to 1.04 for UV/HSO5− and 1.0 for UV/H2O2, resulted in greater efficiency of UV/S2O82− for both DEA and DIA degradation. The second-order rate constants of DEA and DIA with SO4− were calculated to be (6.42±0.12)×108 and (1.70±0.30)×109 M−1s−1, and that with OH were (1.14±0.09)×109 and (2.22±0.44)×109 M−1s−1, respectively, suggesting a strong impact of side chains toward radical reactions. Fe2+ promoted slightly the activation of the examined peroxides at pH 7.4. Presence of organic matter and alkalinity in field water samples negatively influenced the efficiency of UV/S2O82−. Based on the identified degradation by-products by GC–MS, potential degradation pathways were proposed for both compounds. The results obtained suggested that DEA and DIA can be efficiently removed from the contaminated water by OH and SO4− based-AOPs.

Localized polymerization using single photon photoinitiators in two-photon process for fabricating subwavelength structures

Localized polymerization in subwavelength volumes using two photon dyes has now become a well-established method for fabrication of nano structures. Unfortunately, the two photon absorption dyes used in such process are not only expensive but also proprietary. Lucirin TPO-L is an inexpensive, easily available single photon photoinitiator and has been used extensively for single photon absorption of UV light for polymerization. These polymerization volumes however are not localized and extend to micron size resolution having limited applications. We have exploited high quantum yield of radicals of Lucirin TPO-L for absorption of two photons to achieve localized polymerization in subwavelength volumes, much below the diffraction limit. Critical concentration (10 wt%) of Lucirin TPO-L in acrylate (Sartomer) was found optimal to achieve subwavelength localized polymerization and has been demonstrated by fabricating 2D/3D complex nanostructures and functional devices such as variable polymeric gratings using two photon processes. Systematic studies on influence of Lucirin TPO-L concentration on two photon polymerization of Sartomer show that resolution of the fabricated structures critically depends on loading of Lucirin TPO-L. This is expected to unleash the true potential of two photon polymerization for fabrication of complex polymeric nano devices at a larger scale.

Photochemical study of Eosin-Y with PAMAM dendrimers in aqueous solution

A steady-state and time-resolved study of the xanthene dye Eosin-Y (Eos) in the presence of amino-terminated polyamidoamine (PAMAM) dendrimers in alkaline aqueous solution is presented. Stationary photolysis experiments in deaerated and air equilibrated solutions were carried out. The absorption spectra of the photolyzed solutions in the absence of oxygen showed the formation of several intermediate species. With the aid of laser flash photolysis technique (LFP) those transients could be ascribed to semireduced and partially debrominated species of Eos. The triplet quenching rate-constant (3kq) and radical quantum yields (ΦR) were determined by LFP. In the presence of PAMAM, the triplet lifetime of Eos is greatly decreased and the data fitted to a Stern–Volmer treatment. These experiments indicated that the electron transfer from dendrimers to Eos is a highly favored process. Based on the results found in this work, we concluded that Eos/PAMAM couple might act as a promising photoinitiator of vinyl polymerization with low ecological impact.

Radical mechanism of azo cleavage for monoazo reactive dyes, a QSPR study: the similarity between photoreduction on polyamide substrates and thermal reduction in aqueous dithionite solutions

The same radical mechanism occurs in reductive azo cleavage via monohydrogenated radicals generated as the starting reactants in photo‐ and thermal (by dithionite) reduction on a nylon 6 substrate and in aqueous and alcoholic solutions. The rates of photo‐ and thermal azo cleavage in the solid and liquid phases have been thermochemically analysed by calculating the heats of formation of the reactants, intermediates, and products for (1) intramolecular hydrogen transfer (self‐decomposition via rearrangement) in the photo‐ and radically induced hydrazinyl radicals as well as for (2) the disproportionation (redox reaction) between the radicals via a molecular orbital method. The rates of reductive fading (or azo cleavage) are controlled by the heats of reaction via reaction pathways (1) and (2) as well as by rearrangement, depending on the reaction system. Photoreduction of these dyes on polyamide generated the same end products – diazo components and iminooxoquinones from the coupling component – as the products of thermal reduction in aqueous sodium dithionite and of photoreduction in the liquid phase. Photofading on polyamide substrates owing to continuous irradiation is controlled by three factors: the quantum yield of photoinduced hydrazinyl radicals, its rearrangement processes, and the heats of reaction for the thermal azo cleavage reactions via the two pathways. These factors may become molecular descriptors that correlate the rates of fading with molecular structures. The present study may become an introductory trial to construct quantitative structure–property relationship modelling for reduction‐fast azo dyes.

Optimization of a Safranine O three-component photoinitiating system for use in holographic recording

The coupling between a holographic resin, combining multiple monomers and additives, with photoinitiating systems (PIS) is not straightforward. In this paper, a classic PIS based on Safranine O (SFH+) as dye, an amine (ethyl-4-(dimethylamino)benzoate) as electron donor, and a triazine derivative (2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine) as electron acceptor for holographic recording was studied using time-resolved spectroscopic experiments. By taking into account the viscosity of the matrix, a method to evaluate the overall quantum yield of radicals released is proposed and the contribution of singlet and triplet excited states of SFH+ in the formation of radicals is evaluated. Then the corresponding photopolymerization efficiencies of the PIS, studied by real-time FTIR, are compared with holographic recording experiments: this system allows the formation of a hologram with high diffraction efficiency (0.9) in 3 s of irradiation time. It is shown that besides holographic resin formulation, the photochemistry of PIS also impacts the hologram formation.

A better understanding of hydroxyl radical photochemical sources in cloud waters collected at the puy de Dôme station – experimental versus modelled formation rates

Abstract. The oxidative capacity of the cloud aqueous phase is investigated during three field campaigns from 2013 to 2014 at the top of the puy de Dôme station (PUY) in France. A total of 41 cloud samples are collected and the corresponding air masses are classified as highly marine, marine and continental. Hydroxyl radical (HO•) formation rates (RHO•f) are determined using a photochemical setup (xenon lamp that can reproduce the solar spectrum) and a chemical probe coupled with spectroscopic analysis that can trap all of the generated radicals for each sample. Using this method, the obtained values correspond to the total formation of HO• without its chemical sinks. These formation rates are correlated with the concentrations of the naturally occurring sources of HO•, including hydrogen peroxide, nitrite, nitrate and iron. The total hydroxyl radical formation rates are measured as ranging from approximately 2 × 10−11 to 4 × 10−10 M s−1, and the hydroxyl radical quantum yield formation (ΦHO•) is estimated between 10−4 and 10−2. Experimental values are compared with modelled formation rates calculated by the model of multiphase cloud chemistry (M2C2), considering only the chemical sources of the hydroxyl radicals. The comparison between the experimental and the modelled results suggests that the photoreactivity of the iron species as a source of HO• is overestimated by the model, and H2O2 photolysis represents the most important source of this radical (between 70 and 99 %) for the cloud water sampled at the PUY station (primarily marine and continental).

High Performance Photoinitiating Systems for Holography Recording: Need for a Full Control of Primary Processes

Optimization of holography recording in photopolymers was studied from the point of view of a quite general process, that is, the photogeneration of radicals. On the basis of a dye/coinitiator photoinitiating system, the effect of primary events and their relative efficiency was investigated with respect to the final overall properties, such as the diffraction efficiency. Quenching of the dye excited states by the borate salts coinitiators exhibits important differences depending on the dye used (Rose Bengal or Safranine O). Keeping in mind that both singlet and triplet states of the dyes can react, and taking into account the viscosity of the matrix, a method to evaluate the overall quantum yield of radicals released is proposed. It is found that this quantum yield well correlates with the maximum rate of photopolymerization. More interestingly, the dose required to obtain a given diffraction efficiency was found to be also governed by the radical quantum yield, showing that the final property is directly governed by primary events. This shed some light on the efficiency of photochemical pathway to generate radicals for use in organic or polymer areas.