Photostabilizing Effect Research Articles

Light‐fueled self‐oscillation of liquid crystal polymer network: Effect of photostabilizers

AbstractThe quest for harnessing light‐induced oscillatory motion, inspired by natural oscillations, has become a focus of scientific attention. Researchers are exploring the use of liquid crystal network (LCN) polymers and their integration with compatible materials as soft actuators. Of particular interest is the utilization of photostabilizers, which play a pivotal role in preserving the polymer against photodegradation. For this, three distinct derivatives of Tinuvin were chosen to explore their influence on the light‐fueled oscillatory motion of LCN polymers when exposed to polarized light to examine the impact of molecular orientation on the resultant motion. The research includes a comprehensive analysis of morphology, FT‐IR spectra, and elastic modulus assessments. The findings indicate that the Tinuvin derivatives along with light polarization have an impact on the resulting oscillatory characteristics. The findings include oscillation frequencies spanning from 8.95 to 14.96 Hz and oscillation amplitudes ranging from 0.47 to 1.73 mm. The dipole moment of Tinuvin types influences the oscillation frequency by altering the elastic modulus of the LCN, while its impact on surface roughness and structural configuration affects the resulting oscillation amplitude. Notably, the highest oscillation frequency is observed when all oriented molecules within the LCN respond to 45° polarized light. Investigating the impact of utilized photostabilizers on the polymer structural configuration was although possible through the examination of related FT‐IR specra.

Vitamin C for Photo-Stable Non-fullerene-acceptor-Based Organic Solar Cells.

The recent advent of the new class of organic molecules, the so-called non-fullerene acceptors, has resulted in skyrocketing power conversion efficiencies of organic solar cells. However, rapid degradation occurs under illumination, particularly when photocatalytic metal oxide electron transport layers are used in these devices. We introduced vitamin C (ascorbic acid) into the organic solar cells as a photostabilizer and systematically studied its photostabilizing effect on inverted PBDB-T:IT-4F devices. The presence of vitamin C as an antioxidant layer between the ZnO electron transport layer and the photoactive layer strongly suppressed the photocatalytic effect of ZnO that induces NFA photodegradation. Upon 96 h of exposure to AM 1.5G 1 Sun irradiation, the reference devices lost 64% of their initial efficiency, while those containing vitamin C lost only 38%. The UV-visible absorption, impedance spectroscopy, and light-dependent voltage and current measurements reveal that vitamin C reduces the photobleaching of NFA molecules and suppresses the charge recombination. This simple approach using a low-cost, naturally occurring antioxidant, provides an efficient strategy for improving photostability of organic semiconductor-based devices.

Studying the photodecomposition rate constant and morphology properties of modified poly(vinyl chloride) with novel Schiff's bases

AbstractThe photodegradation of a poly(vinyl chloride) (PVC) film filled with Schiff bases in its structure was investigated and studied by comparing it with a blank PVC film. A PVC film containing novel Schiff's bases was synthesized and used as a photostabilizer for PVC. PVC was exposed to ultraviolet light and underwent harmful changes, where the photostabilization effect differed before and after filling aromatic Schiff bases within the structure. After 300 h of UV irradiation, the photodecomposition rate constants were calculated to identify the impact of Schiff bases on PVC films. In order to evaluate the impact of adding Schiff bases as photo‐stabilizers, the evolution of different functional groups during irradiation was monitored using FTIR spectra. Also, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were exploited to examine the surface morphology of produced polymers. These investigations showed that filling novel Schiff bases inside the polymers performed much better photostabilization than plain PVC. Hence, the photodecomposition rate constant, on the other hand, was calculated alongside the irradiation time.

New organic PVC photo-stabilizers derived from synthesised novel coumarine moieties

New four coumarin derivatives (9–12) compounds have been successfully synthesized from the reaction of salicyaldehyde and ethylacetoacetate yielding 3-acetyl coumarine, which on further treatment with bromine/chloroform gave 3-(2-Bromoacetyl) coumarine. Substituted 4-(Benzylidene-amino)-]triazole-3-thiol reacted with 3-(2-Bromoacetyl) coumarine to give 3-sulfanyl-acetyl-4-(Benzylidene-amino)-triazol related coumarin derivatives. The newly synthesized products were characterized with FTIR,1H and13C NMR, and energy dispersive X-ray spectra to confirm their chemical structures. All above used techniques demonstrated the formation of target products with high percentage of purity. The synthesised compounds (9–12) have been investigated as organic additives to protect poly(vinyl chloride) (PVC) from photo-degradation at (λmax = 313 nm) and irradiation period 300 h in the atmosphere. The stabilizing efficiencies of blended PVC films were examined by detecting changes in their infrared spectra, weight, and average molecular weight viscosity. A light microscope, atomic force microscopy, and a scanning electron micrograph were all used to examine the surface morphology of the films. The additives enhanced considerable resistance of films against irradiation and the polymeric surface was significantly smoother in the presence of the coumarine derivatives compared with the blank film. The strongest photo-stabilization effect was seen in coumarine derivative (12) containing 2-hydroxy naphthol the most effective as UV absorber, free radical scavenger, and quencher. This phenomenon appears to allow energy to be transported through resonant aryl rings and various intersystem crossover mechanisms.

Study of UV ageing effects in modern artists’ paints with MeV-SIMS

In the present work, alkyd and acrylic self-made paints containing synthetic organic pigments (SOPs) of different chemical classes (phthalocyanine, quinacridone, and diketopyrrolo-pyrrole) were analysed by Secondary Ion Mass Spectrometry with MeV primary ions (MeV-SIMS) to study the chemical changes that occur due to accelerated UV ageing. MeV-SIMS is an emerging accelerator-based, surface-sensitive mass spectrometry technique that can provide information about the chemical composition in the uppermost layers of materials. Two-component mock-up samples were prepared and aged for two and four months, to mimic environmental ageing over periods of one and two years. The obtained results show that the studied SOPs are stable under the accelerated ageing conditions used in this study and that they can be easily identified in aged paints, while the binder components undergo structural changes due to the photodegradation processes. The kinetics of binder degradation were found to be dependant on the pigment present in the paint, with phthalocyanines having the highest photostabilizing effect amongst the pigments studied. In addition, the acrylic binder exhibited slightly higher stability to UV ageing than the alkyd medium. This study allowed the identification of SOPs and binders in the selected contemporary artworks, which date from different periods and belong to both outdoor and indoor collections.

Photokinetics of oil soluble 1,3,5-Triazine UV filters in combination with Butyl Methoxydibenzoylmethane or with Diethylamino Hydroxybenzoyl Hexyl Benzoate

Bis-ethylhexyloxyphenol Methoxyphenyl Triazine (BEMT) was previously shown to efficiently quench the excited state of Butyl Methoxydibenzoylmethane (BMDBM) and to prevent its photodegradation. However, little is known on the consequences for the quenching molecule in this process. In this study we examined the impact of BMDBM on the photokinetics of the quencher BEMT by HPLC measurements and determination of the rate constant. We extended the investigation to Ethylhexyl Triazone (EHT) and Diethylhexyl Butamido Triazone (DBT), two 1,3,5-Triazine filters that became standardly used UVB filters in systems with BMDBM and without Octocrylene (OCR). We performed DFT computations on each studied UV filter to identify possible photostabilization mechanisms within the binary systems. Additionally, we evaluated the number of free radicals formed in formulations containing the studied mixtures. The same investigation was carried out with Diethylamino Hydroxybenzoyl Hexyl Benzoate (DHHB) as an alternative UVA filter to BMDBM. Our experiments showed that EHT and DBT own no capability in photostabilizing BMDBM but confirmed the photostabilization effect of BEMT on BMDBM. At the same time, our work revealed a photodestabilization effect of BMDBM on BEMT, EHT and DBT as well as an increased UV-induced number of free radicals in the formulations containing the binary mixture of the 1,3,5-Triazine UV filters and BMDBM. This is hypothesized to be the consequence of chain reactions following the production of free radicals of destabilized BMDBM. In contrary to BMDBM, DHHB photostabilized the three 1,3,5-Triazine filters BEMT, EHT and DBT completely. Corresponding results of quantum computations predicted efficient triplet-triplet energy transfer to DHHB. No free radicals could be detected after UV exposure in the formulations containing the binary combination of BEMT, EHT, DBT with DHHB in contrast to formulations containing binary combinations with BMDBM.

Characterization of Fluorescent Proteins with Intramolecular Photostabilization*.

Genetically encodable fluorescent proteins have revolutionized biological imaging in vivo and in vitro. Despite their importance, their photophysical properties, i. e., brightness, count‐rate and photostability, are relatively poor compared to synthetic organic fluorophores or quantum dots. Intramolecular photostabilizers were recently rediscovered as an effective approach to improve photophysical properties of organic fluorophores. Here, direct conjugation of triplet‐state quenchers or redox‐active substances creates high local concentrations of photostabilizer around the fluorophore. In this paper, we screen for effects of covalently linked photostabilizers on fluorescent proteins. We produced a double cysteine mutant (A206C/L221C) of α‐GFP for attachment of photostabilizer‐maleimides on the β‐barrel near the chromophore. Whereas labelling with photostabilizers such as trolox, a nitrophenyl group, and cyclooctatetraene, which are often used for organic fluorophores, had no effect on α‐GFP‐photostability, a substantial increase of photostability was found upon conjugation to azobenzene. Although the mechanism of the photostabilizing effects remains to be elucidated, we speculate that the higher triplet‐energy of azobenzene might be crucial for triplet‐quenching of fluorophores in the blue spectral range. Our study paves the way for the development of fluorescent proteins with photostabilizers in the protein barrel by methods such as unnatural amino acid incorporation.

Photostabilization Effect of Pyrazolone Azo Dyes on IR Absorbers in Polymer Films

Photostabilization Effect of Pyrazolone Azo Dyes on IR Absorbers in Polymer Films

Tin Complexes Containing an Atenolol Moiety as Photostabilizers for Poly(Vinyl Chloride)

The lifetime of poly(vinyl chloride) (PVC) can be increased through the addition of additives to provide protection against irradiation. Therefore, several new tin complexes containing atenolol moieties were synthesized and their photostabilizing effect on PVC was investigated. Reacting atenolol with a number of tin reagents in boiling methanol provided high yields of tin complexes. PVC was then mixed with the tin complexes at a low concentration, producing polymeric thins films. The films were irradiated with ultraviolet light and the resulting damage was assessed using different analytical and surface morphology techniques. Infrared spectroscopy and weight loss determination indicated that the films incorporating tin complexes incurred less damage and less surface changes compared to the blank film. In particular, the triphenyltin complex was very effective in enhancing the photostability of PVC, and this is due to its high aromaticity (three phenyl rings) compared to other complexes. Such an additive acts as a hydrogen chloride scavenger, radical absorber, and hydroperoxide decomposer.

Spectroscopic and Morphological Study of Irradiated PVC Films Doped with Polyphosphates Containing 4,4'-Methylenedianiline

Polyphosphates containing 4,4'-methylenedianiline moiety were synthesized and their use as polyvinyl chloride (PVC) additives to enhance PVC photostability was investigated. Polyphosphates (0.5 wt %) were mixed with PVC and thin films (50 μm thickness) were prepared. The films were subjected to long-term exposure to ultraviolet light at room temperature to investigate the photostabilizing effects of the polyphosphates. Following irradiation, the intensities of the peaks corresponding to several functional groups in the PVC blends were analyzed using infrared spectroscopy. Additionally, changes in the mass and molecular weight as well as the appearance of defects (e.g., cracks, roughness, and irregularities) in the irradiated PVC blends were evaluated. It was found that polyphosphates inhibited photodecomposition of PVC. It was determined that polyphosphates exhibiting ortho-geometry were particularly effective in stabilizing the PVC blends. Notably, polyphosphates acted as ultraviolet light absorbents, radical scavengers, and peroxide decomposers. The synthesized polyphosphates are highly stable and provided PVC film protection comparable with those previously reported for related polyphosphates, Schiff bases and organometallics.

Synthesis of multifunctional core–shell toughening agent with light stability and its application in polycarbonate

ABSTRACTA light stabilizer compound of 2‐(2′‐propionyloxy‐5′‐methylphenyl) benzotriazole (AMB) was synthesized by the esterification of the 2‐(2′‐hydroxy‐5′‐methylphenyl) benzotriazole with acryloyl chloride (AC), and the AMB was then copolymerized with the methyl methacrylate (MMA), butyl acrylate (BA), and silicone monomers (D4) to prepare the silicone light toughener of poly(D4‐MMA‐BA‐AMB). Effects of the AMB monomer on the conversion and polymerization stability and the toughening and photostabilizing effects of the poly(D4‐MMA‐BA‐AMB) on the polycarbonate (PC) were studied. The prepared multifunctional toughening agent was characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermogravimetric analyzer, transmission electron microscopy, dynamic light scattering analyzer, and ultraviolet absorption spectroscopy. Results show that the prepared poly(D4‐MMA‐BA‐AMB) toughening agent possessed core–shell structure and could effectively absorb the ultraviolet rays. Although the addition of the poly(D4‐MMA‐BA‐AMB) toughening agent had a negative effect on the tensile strength of the PC, it could greatly improve the low‐temperature notched impact strength, toughness performance, and yellowness performance of PC products after UV irradiation. Compared with the silicone toughening agent, the toughening agent of the poly(D4‐MMA‐BA‐AMB) had better anti‐ultraviolet property for the PC/poly(D4‐MMA‐BA‐AMB) composite. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48747.

Insights into the photochemistry of 5-aminotetrazole derivatives with applications in coordination chemistry. Effect of the saccharyl moiety on the photostability

Abstract The properties and applications of 2-methyl-(2H)-tetrazole-5-amino-saccharinate (2MTS) in catalysis and chelant-based chemotherapy stimulated investigations on its photostability. The photochemistry of monomeric 2MTS in solid argon (15 K) was compared with those of 2-methyl-(2H)-tetrazole-5-amine (2MT) and 1-methyl-(2H)-tetrazole-5-amine (1MT). Compounds were subjected to in situ narrowband UV-irradiation at different wavelengths. Reactions were followed by infrared spectroscopy, supported by B3LYP/6-311++G(d,p) calculations. Photochemical pathways for 2MT and 2MTS proved similar but photodegradation of 2MTS was 20× slower, unraveling the photostabilizing effect of the saccharyl moiety that extends into the nitrilimine formed from 2MTS and its antiaromatic 1H-diazirene isomer, which proved photostable at 290 nm, unlike the 1H-diazirene formed from 2MT. Analysis of the photochemistries of 2MTS/2MT (250 nm) and 1MT (222 nm), including energy trends calculated for the isomeric C2H5N3 species postulated/observed from photolysis and EPR results, enabled a deeper insight into the photodegradation mechanisms of 1,5-substituted and 2,5-substituted tetrazoles. We postulate a pivotal singlet state imidoylnitrene species, sN1, as common intermediate, which undergoes a Wolff-type isomerization to a stable carbodiimide. Photo-extrusion of N2 from 1,5-substituted tetrazoles generates sN1 directly but from 2,5-substituted tetrazoles it originates a nitrilimine, then a diazirene, which finally leads to sN1. Selective formation of cyanamide from 1MT requires photoisomerization between sN1 and sN2, accessible at 222 nm. EPR studies enabled the detection of methyl nitrene, arising from photolysis of 1H-diazirene intermediate.

The Morphology and Performance of Poly(Vinyl Chloride) Containing Melamine Schiff Bases against Ultraviolet Light.

Five Schiff bases derived from melamine have been used as efficient additives to reduce the process of photodegradation of poly(vinyl chloride) films. The performance of Schiff bases has been investigated using various techniques. Poly(vinyl chloride) films containing Schiff bases were irradiated with ultraviolet light and any changes in their infrared spectra, weight, and the viscosity of their average molecular weight were investigated. In addition, the surface morphology of the films was inspected using a light microscope, atomic force microscopy, and a scanning electron micrograph. The additives enhanced the films resistance against irradiation and the polymeric surface was much smoother in the presence of the Schiff bases compared with the blank film. Schiff bases containing an ortho-hydroxyl group on the aryl rings showed the greatest photostabilization effect, which may possibly have been due to the direct absorption of ultraviolet light. This phenomenon seems to involve the transfer of a proton as well as several intersystem crossing processes.

The Effect of Red Pigment and Photo Stabilizers on the Photo Degradation of Polypropylene Films

The aim of this work was to evaluate the photo degradation of PP films containing photo stabilizers, a ultraviolet absorber and a hindered amine light stabilizer (HALS), and a red pigment. The films were produced by extrusion and exposed to the UV radiation in the laboratory for up to 15 weeks. The results obtained from FTIR, UV-vis and colorimetry showed that the pigment reduced the rate of chemical degradation both in non-stabilized and photo stabilized films, and the influence was more significant for the combination of pigment and HALS. However, the color shift was more evident when the pigment was present, suggesting that this additive may suffer chemical rearrangements during exposure but do not generate free radicals that can initiate degradation of the polymer. The mechanical properties of the films followed the same trend as the other results, but the unexposed films showed a peculiar behaviour, with much higher tensile strength when the pigments were present. X-ray diffraction and DSC analyses suggested that this might be related to differences in crystal structure.

Stability of acrylic polyurethane coatings under accelerated aging tests and natural outdoor exposure: The critical role of the used photo-stabilizers

The effect of photo-stabilizers on the crosslinking and weathering durability of acrylic polyurethane coatings based on the HSU 1168 acrylic polyol and the Desmodur N-75 polyisocyanate has been investigated. The aging of these coatings under accelerated weathering conditions and natural outdoor conditions upto a decade has been compared. Our findings showed that photo-stabilizers had a negligible effect on the conversion of isocyanate groups during the photocroslinking but enhanced the aging resistance. Coatings containing photo-absorbers exhibited an excellent weathering durability, upto 72 cycles upon accelerated aging and 10 years in natural outdoor exposure, while the unstabilized coatings appeared serious cracks, damages and chalking after 48 cycles of accelerated aging and after 5 years in outdoor weathering exposure. The degradation of coatings was also investigated by monitoring atomic force microscopy, weight loss and gloss loss, cracking, blistering and flacking of the coating. The degradation of coatings in the surface of natural and accelerated was compared by using Atomic force microscopy coupling with naonoscale infrared spectroscopy (AFM- IR) by following oxidized products on the coating surface.

Synthesis, Structure, and Cytotoxicity of a New Sulphanyl-Bridged Thiadiazolyl-Saccharinate Conjugate: The Relevance of S⋅⋅⋅N Interaction.

Reports showing that the copper concentration is considerably higher in neoplasms than in normal tissues prompted the need to develop selective copper chelators. We disclosed recently that some N-linked tetrazole-saccharinates bind selectively to copper, forming complexes that are highly cytotoxic towards cancer cells. Because tetrazole-saccharinates are photolabile, due to the photoreactivity of tetrazoles, we proposed thiadiazolyl-saccharinates as an alternative. Herein we describe the synthesis, structure, and monomeric photochemistry of a sulphanyl-bridged thiadiazolyl-saccharinate, 3-[(5-methyl-1,3,4-thiadiazol-2-yl)sulphanyl]-1,2-benzothiazole 1,1-dioxide (MTSB). The monomeric structure, charge density analysis, and characteristic infrared spectrum of MTSB were investigated theoretically, using quantum chemical calculations, and also experimentally, using matrix-isolation infrared spectroscopy. The crystal structure was investigated by combining X-ray crystallography with infrared and Raman spectroscopies. Results show that the structure of isolated MTSB is similar to that found in the crystal, with an S⋅⋅⋅N interaction clearly contributing to the structure of the molecule and of the crystal. Matrix irradiation revealed a high photostability of MTSB, compared to parent tetrazole-saccharinates and to the 5-methyl-1,3,4-thiadiazole building block, emphasizing the photostabilizing effect of the saccharyl system. Finally, in vitro toxicity assays of MTSB showed a copper concentration-dependent toxicity against cancer cells, without affecting normal cells. In particular, MTSB was most effective towards the hepatic (HepG2), neuroblastoma (SH-SY5), and lymphoma cell lines (U937). Thus, MTSB represents a promising lead for cancer chemotherapy based on chelating agents.

Investigation of Photodegradation of High-Density Polyethylene Containing Cyclohexyl Phosphonic Acid and Its Nickel Salts

A study on the character of influence of organic derivatives of quinquevalent phosphorus (cyclohexyl phosphonic acid and its nickel salts) on photodegradation of high-density polyethylene is performed. It is established that organophosphorus compounds demonstrate both photostabilizing and photocatalytic degradation effects toward polyethylene.

Lignosulfonate Improves Photostability and Bioactivity of Abscisic Acid under Ultraviolet Radiation.

Abscisic acid (ABA), as a commonly used plant growth regulator, is easy to be degraded and lose its bioactivity under sunshine. To select an eco-friendly and efficient photoprotectant for the improvement of photostability and bioactivity of ABA when exposed to ultraviolet (UV) light, we tested the effects of three biodegradable natural-derived high polymers, sodium lignosulfonates 3A [molecular weight (MW) > 50000, with degree of sulfonation (DS) of 0.48] and NA (20000 < MW < 50000, with DS of 0.7) and calcium lignosulfonate CASA (MW < 20000, with DS of 0.7), on the photodegradation of ABA. Lignosulfonates 3A, NA, and CASA showed significant photostabilizing capability on ABA. Lignosulfonate 3A showed preferable photostabilizing effects on ABA compared to CASA, while NA showed an intermediate effect. That indicated that lignosulfonate with a high MW and low DS had a stronger UV absorption and the hollow aggregate micelles formatted by lignosulfonate protect ABA from UV damage. Approximately 50% more ABA was kept when 280 mg/L ABA aqueous solution was irradiated by UV light for 2 h in the presence of 2000 mg/L lignosulfonate 3A. The bioactivity on wheat (JIMAI 22) seed germination was greatly kept by 3A in comparison to that of ABA alone. The 300 times diluent of 280 mg/L ABA plus 2000 mg/L 3A after 2 h of irradiation showed 20.8, 19.3, and 9.3% more inhibition on shoot growth, root growth, and root numbers of wheat seed, separately, in comparison to ABA diluent alone. We conclude that lignosulfonate 3A was an eco-friendly and efficient agent to keep ABA activity under UV radiation. This research could be used in UV-sensitive and water-soluble agrichemicals and to optimize the application times and dosages of ABA products.

A study on the photostabilizer additives on the textile fiber reinforced polymer composites: Mechanical, thermal, and physical analysis

The effect of photostabilizers on the mechanical, thermal, and physical properties of textile fiber reinforced polymer (T‐FRP) composites was investigated. In the first phase of this study, the effect of different concentrations of ultra violet absorber (UVA), hindered amine light stabilizers (HALS) and antioxidants (AOs) into T‐FRP composites for unweathering condition are examined. Mechanical tests were performed as well as differential scanning calorimetry (DSC) analysis for thermal properties. According to test results, there is no significant effect of photostabilizers on the mechanical and thermal properties of the T‐FRP composites. In the second phase of the study, the influence of the photostabilizers on the durability performance of T‐FRP composites is focused under the accelerated UV weathering condition by the help of tensile testing, thermal analysis, and color measurements. According to test results, only about 5% loss in mechanical properties (25% loss for composites without additives) can be observed after 240 h of UV weathering with HALS and UVA addition at adequate concentrations. In addition, AOs can be considered as a strong stabilizer on physical properties with lower color change values. This work shows that the efficiency of the photostabilizers is highly dependent on the type, concentration, and weathering time. POLYM. ENG. SCI., 58:1082–1090, 2018. © 2017 Society of Plastics Engineers

Diethylamino hydroxybenzoyl hexyl benzoate (DHHB) as additive to the UV filter avobenzone in cosmetic sunscreen formulations - Evaluation of the photochemical behavior and photostabilizing effect

The aim of the present study was to investigate the photochemical behavior of DHHB and its photostabilizing effect on avobenzone (AVO) in different sunscreen formulations. The formulations were subjected to photostability studies by HPLC and spectrophotometry. In vitro phototoxicity was assessed using 3T3 fibroblast cultures. The mechanism of interaction between DHHB and AVO was investigated by steady state and time-resolved fluorescence spectroscopy. All formulations provided ultra-protection against UVA radiation. HPLC results demonstrated that DHHB did not present a photostabilizing effect on AVO. Fluorescence spectroscopy showed that AVO and DHHB interact by a static quenching mechanism and DHHB did not affect the AVO excited state lifetime. In addition, the energy transfer by Förster mechanism (FRET), which is the most often mechanism responsible for singlet-singlet quenching, is unlikely in this work. These results suggest why DHHB did not work as a photostabilizer on AVO singlet excited state. Phototoxicity results demonstrated that combinations containing DHHB (C2) did not show a phototoxic potential. Finally, although DHHB was considered to be photostable for all formulations studied (F2 and F3) it did not increase the photostability of AVO (F3). Thus, we suggested that formulations containing DHHB (F2) should be considered more advantageous than formulations containing AVO and AVO/DHHB (F1 and F3 respectively).