Biphotonic Process Research Articles

Reinvestigation on the UV/sulfite oxidation of organic pollutants: The overlooked role of excited states and bromate control

Reinvestigation on the UV/sulfite oxidation of organic pollutants: The overlooked role of excited states and bromate control

Biochemical reactions remote-sensitized by excitons propagating across macroscopic distances along biological fibers: Isomerization of 11-cis-retinal

Biochemical reactions remote-sensitized by excitons propagating across macroscopic distances along biological fibers: Isomerization of 11-cis-retinal

Rapid degradation of chloroquine derivatives in a novel advanced reduction process: Role of intramolecular hydrogen bond in the formation of excited triplet state compound

The role of triplet excited state compounds (TESC) in contaminants degradation by advanced reduction processes (ARPs) is rarely reported. In this study, Salicylic acid derivatives (SAD, e.g. Salicylic Acid (SA) and Sulfosalicylic acid (SSA)) were applied in ultraviolet activated sulfite process (UV/Sulfite) to generate TESC and enhance the decomposition of chloroquine derivatives (CQD, antiviral drugs being used for treating COVID-19 infection, e.g. chloroquine phosphate (CP)). The results indicated that the pseudo 1st order rate constant of CP (kobs-CP) increased by 2.76 and 6.26 fold, which increased from 9.10 × 10–4 s–1 in UV/Sulfite process to 2.51 × 10–3 s–1, 5.72 × 10–3 s–1 in UV/Sulfite/SA and UV/Sulfite/SSA process respectively. Similar phenomena were observed in other CQDs. Transient absorption spectra demonstrated that both triplet excited state SAD (3SAD*) and hydrated electron (eaq–) were the reactive intermediates in UV/Sulfite/SAD process, and contribute to the abatement of CP. The enhancement of SAD on contaminants degradation in UV/Sulfite/SAD process could attribute to the strong acceleration of eaq– toward the formation of 3SAD* in its photosensitive process, where SAD with intramoleuclar hydrogen bond would not undergo a directly photoionization process after absorbing a photon but undergo intersystem crossing to transform into 3SAD* which was then ionized to eaq– by biphotonic process, and constitute a hydrated electrons mediated photosensitization cycle with the supplement of eaq– from UV/Sulfite process. The higher CP degradation rate in UV/Sulfite/SSA process than that in UV/Sulfite/SA process was ascribed to a higher second order rate constant of 3SSA* toward CP and a higher yield of 3SSA*, which resulted from its higher intramolecular hydrogen bond energy enhancing photosensitization and photoionization.

Recent applications of biphotonic processes in organic synthesis

Organic synthesis mediated by biphotonic processes has gained great momentum in the last five years. Herein, an overview of the existing examples is reported.

Can the symmetrical Dewar pyridine be observed experimentally? A theoretical study

ABSTRACTIn this work we study the possibility of the photochemical formation of the symmetrical Dewar pyridine (1-azabicyclo-[2,2,0]-hexa-2,5-diene), by applying the complete active space self-consistent field method and the multiconfigurational second-order perturbation theory to explore the corresponding ground and excited state potential energy surfaces. According to our theoretical calculations there are three possible paths that can be followed, one is a biphotonic process which involves irradiating pyridine in its ground state with a 358 nm laser guiding the system to an intersystem crossing S1/T1/S0 of triple character whereby deactivation to the ground state, S0, Dewar minimum occurs, the second one, which is a ground state thermal reaction involves the use of a far-Infra-Red laser where planar pyridine is vibrationally excited to a very high vibrational level whose energy is comparable to that of the ground state transition structure, S0(TS), connecting the symmetrical S0 Dewar pyridine and the ground state of planar pyridine. The third process is also a biphotonic one involving excitation of planar pyridine with an energy which is in the limits of its ionisation potential. In this case there is a theoretically accessible S1/S0 Conical Intersection which leads directly to the ground state of the symmetrical Dewar pyridine.

Reduction of dinitrotoluene by hydrated electrons generated from UV irradiation of toluene in wastewater: Towards cleaner production

Abstract This study presents a sustainable approach for degrading dinitrotoluene to diaminotoluene in wastewater without the production of a secondary pollutant, to achieve cleaner production. This process eliminates the chemical oxygen demand of the pre-treated wastewater and ensures that the treated wastewater is reusable. In this study, the hydrated electron generated from the toluene/UV process at 254 nm in simulated wastewater, and the mechanism of its production were investigated. This mechanism demonstrated that intermediate benzyl radicals can continuously facilitate the generation of hydrated electrons by absorbing two photons during the UV process. In addition, the hydrated electron production via the photolysis of toluene resulted from the triplet state via a biphotonic process. To detect the hydrated electrons in aqueous solution, monochloroacetic acid and chloroethanol were applied. By studying the operating parameters, it was revealed that the hydrated electron generation efficiency was pH dependent, and the complete degradation of dinitrotoluene was achieved at an optimum pH of 7.5. Furthermore, the elimination of the remaining chemical oxygen demand related to the reduction process in simulated wastewater was investigated using heat-activated persulfate; through this advanced oxidation process, the chemical oxygen demand was almost completely eliminated. Depending on the pH and the model solution based on the wastewater composition, the proposed treatment technique, which is novel and environmentally friendly, can be applied to large-scale plants.

Synchronized biphotonic process triggering C[sbnd]C coupling catalytic reactions

Activation of aryl(Ar)-halides for CC coupling catalytic reactions using visible light has become one of the most challenging tasks in organic synthesis since it offers effective and safer alternatives to traditional dehalogenation protocols. The insufficient energy provided by visible light to cleave such strong CH alogen bonds certainly makes necessary the development of new protocols to overcome this limitation. We report here the application of photon upconversion (UC) technology based on triplet-triplet annihilation (TTA) to a CC coupling catalytic reaction, a possibility that has not been investigated to date. This synchronized biphotonic process (TTA-UC) activates successfully Ar-halides with visible light. Based on product analysis and spectroscopic experiments, a cascade process combining photophysical and photochemical steps is proposed for the mechanism rationalization. Visible light, ambient temperature and pressure, low-loading metal-free photocatalysts and no additives make this protocol very attractive for applications to the synthesis of fine chemical building blocks, pharmaceuticals, agrochemicals or new materials.

Synthesis and Upconversion Emission of β-Ca2SiO4: (Er3+, Yb3+)

The β-Ca2SiO4: (Er3+, Yb3+) powders were synthesized by the simple solid-state process. The obtained samples were given characterizations of X-ray diffraction, Fourier-transform infrared, transmission electron microscopy, and luminescence. The samples have monoclinic parawollastonite phase and irregular morphology. Under the excitation at 980 nm, the obtained β-Ca2SiO4: (Er3+, Yb3+) samples show the intense upconversion (UC) emission. The dosage of Yb3+ has obvious influence on the emission intensities of β-Ca2SiO4: (Er3+, Yb3+) samples. Also, the emission intensity increases gradually with the increasing pump power from 350 to 600 mW. On the basis of luminescent properties of samples, we can conclude that the UC emission originates from the biphotonic process.

A density functional theory and spectroscopic study of intramolecular quenching of metal-to-ligand charge-transfer excited states in some mono-bipyridine ruthenium(II) complexes

The complexes [Ru(NCCH3)4bpy]2+ and [Ru([14]aneS4)bpy]2+ ([14]aneS4 = 1,4,8,11-tetrathiacyclotetradecane, bpy = 2,2′-bipyridine) have similar absorption and emission spectra but the 77 K metal-to-ligand charge-transfer (MLCT) excited state emission lifetime of the latter is less than 0.3% that of the former. Density functional theory modeling of the lowest energy triplet excited states indicates that triplet metal centered (3MC) excited states are about 3500 cm−1 lower in energy than their 3MLCT excited states in both complexes. The differences in excited state lifetimes arise from a much larger coordination sphere distortion for [Ru(NCCH3)4bpy]2+ and the associated larger reorganizational barrier for intramolecular electron transfer. The smaller ruthenium ligand distortions of the [Ru([14]aneS4)bpy]2+ complex are apparently a consequence of stereochemical constraints imposed by the macrocyclic [14]aneS4 ligand, and the 3MC excited state calculated for the unconstrained [Ru(S(CH3)2)4bpy]2+ complex (S(CH3)2 = dimethyl sulfide) is distorted in a manner similar to that of [Ru(NCCH3)4bpy]2+. Despite the lower energy calculated for its 3MC than 3MLCT excited state, [Ru(NCCH3)4bpy]2+ emits strongly in 77 K glasses with an emission quantum yield of 0.47. The emission is biphasic with about a 1 μs lifetime for its dominant (86%) emission component. The 405 nm excitation used in these studies results in a significant amount of photodecomposition in the 77 K glasses. This is a temperature-dependent biphotonic process that most likely involves the bipyridine-radical anionic moiety of the 3MLCT excited state. A smaller than expected value found for the radiative rate constant is consistent with a lower energy 3MC than 3MLCT state.

Interaction of Retinoic Acid Radical Cation with Lysozyme and Antioxidants: Laser Flash Photolysis Study in Microemulsion

All-trans retinoic acid (ATRA) plays essential roles in the normal biological processes and the treatment of cancer and skin diseases. Considering its photosensitive property, many studies have been focused on the photochemistry of ATRA. In this study, we investigated the transient phenomena in the laser flash photolysis (LFP) of ATRA in microemulsion to further understand the photochemistry of ATRA. Results show that 355 nm LFP of ATRA in both acidic and alkaline conditions leads to the generation of retinoic acid cation radicals (ATRA(•+)) via biphotonic processes. The employment of microemulsion system allows us to investigate the reaction of hydrophobic ATRA(•+) with molecules of different polarity. Therefore, we studied the reaction activity of ATRA(•+) to many hydrophobic and hydrophilic molecules. Results show that ATRA(•+) can efficiently interact with lysozyme, tyrosine, tryptophan and many antioxidants, such as curcumin (Cur), vitamin C (VC) and gallic acid (GA). The apparent rate constants of these reactions were measured and compared. These findings suggest that ATRA(•+) is a reactive transient product which may pose damage to lysozyme, and antioxidants, such as Cur, VC and GA, may inactivate ATRA(•+) by efficient quenching reactions.

A single- and double-flash flash photolysis study of the sequential biphotonic photoprocesses of Cu(i) phenanthrolines. Comparison of the helicate complex, [Cu2(1,3-bis(9-methyl-1,10-phenanthrolin-2-yl)propane)2]2+, and [Cu(2,9-dimethyl-1,10-phenanthroline)2]+ photoprocesses

Photochemical processes induced when two photons are sequentially absorbed by the helicate complex [Cu2(mphenpr)2](2+), where mphenpr = 1,3-bis(9-methyl-1,10-phenanthrolin-2-yl)propane, and [Cu(dmp)2](+) were investigated in CH2Cl2 containing solvents. A strong resemblance was observed between the fs-ns photophysics of [Cu2(mphenpr)2](2+) and Cu(I) phenanthroline complexes having a large steric hindrance. In the biphotonic regime, single-flash flash-photolyzed solutions were used for the determination of the product concentrations and quantum yields. The concentration of Cl(-) produced by the photoinduced decomposition of CH2Cl2 increases linearly with flash intensity as expected for a monophotonic process. In contrast, the concentration of a decomposed Cu(I) complex exhibits the quadratic dependence on flash intensity of a biphotonic process. Results of a sequential double-flash flash photolysis experiment are consistent with the decomposition of CH2Cl2 ahead of the flattened excited state formation and with the absorption of the second photon by the flattened MLCT excited state.

Laser flash photolysis studies of tris(2,2′-bipyridine)nickel(II) ion in aqueous solution

Abstract The photoreactions of tris(2,2′-bipyridine)nickel(II) complex, Ni(II)(bpy 3 ) 2+ were studied and compared with that of the photoreactions of 2,2′-bipyridine ligand. Continuous photolysis of the complex shows that the photodecomposition corresponds to the absorption of light by the complex in the ligand centered excited state. Flash photolysis of the complex using a 248 nm excimer laser yields bipyridine cation radical and solvated electron as transients. Absorption spectra of the transient observed for the complex is found to be similar to that observed for the ligand on flash excitation using a 248 nm laser suggesting that the transients observed in the case of complex is due to the coordinated bipyridine in the complex. The formation of solvated electron is observed to be monophotonic and that of the bipyridine cation radical is found to be a biphotonic process. Significant change in Ni–N bond distance upon oxidation of Ni(bpy 3 ) 2+ ion when compared to that observed in nickel(II)tetraazamacrocyclic complexes suggests that the formation of the trivalent complex by photolysis is not favored for the Ni(bpy 3 ) 2+ ion and CTTS excited state in the complex is not observed in the present system.

Observations on the mechanisms of the thermal and photoinduced oxidation of D-mannitol and fucoidan by transition metal complexes and inorganic radicals

The mechanism of the D-mannitol and fucoidan oxidation by •OH, peroxyl radicals, PRX• = , HOCH2 , and CH2(), inorganic radicals, , , and [NiIII(Me6-[14]aneN4)H2O]3+ was investigated by pulse radiolysis. Relative to the diffusion-controlled reaction of the •OH radical, the reactions of PRX•, , and are slow, with a 105–106 (mol L−1)−1 s−1 order of magnitude. The formation of saccharide–Ni(III) complexes also accounts for oxidation of the D-mannitol and fucoidan by [NiIII(Me6-[14]aneN4)H2O]3+. A rate constant k = 2.2 × 107 (mol L−1)−1 s−1 was estimated for the complexation of [NiIII(Me6-[14]aneN4)H2O]3+ by D-mannitol. In addition, both carbohydrates accelerate the decay of the Ni(III) complex which occurs with half life t 1/2 ∼ 102 ms. Consistent with the formation of fucoidan–Cu2+ complexes, the flash irradiations of these complexes at 351 nm produces transient spectra assigned to (n = 2, 3) species. The non-linear dependence of the product concentration on the flash intensity shows that formation of the species is a biphotonic process.

Self-trapped excitonic green emission from layered semiconductors

Crystals of layered semiconductor are grown by Bridgman technique and are studied them under two-photon excitation by a Q-switched 20-ns pulse laser. The photoluminescence (PL) emission spectra of the crystals are measured at various pumping powers and temperatures. The PL spectra appear broad and structureless emissions with their peaks in the green spectral region. The characteristic emissions are from self-trapped excitons of the crystals. An analysis of the spectra measured at various pumping powers shows a quadratic dependence of the PL peak intensity on the power, confirming a biphotonic process of the two-photon pumping. The temperature dependence shows an enhancement of the nonlinear response at low temperatures. The activation energy is estimated and found to be 2.4 meV. The roles of the bound excitons in the observed PL are discussed briefly.

Thermal Effect for the Mesoscopic LC Circuits Including Complicated Coupling by Virtue of GHFT

The Hamilton operator for the mesoscopic LC circuits including complicated coupling is given. Because the practical circuits are inevitably influenced by the external environment, the effect of temperature on the quantum effects for the mesoscopic circuit must be taken into account. Then we discuss the thermal effect of the system by simulating it with the biphotonic process and the contribution of each process to the energy ensemble average by virtue of the generalized Hellmann-Feynman Theorem (GHFT).

Photoreactivity of biologically active compounds. XIX: Excited states and free radicals from the antimalarial drug primaquine

The formation and reactivity of excited states and free radicals from primaquine, a drug used in the treatment of malaria, was studied in order to evaluate the primary photochemical reaction mechanisms. The excited primaquine triplet was not detected, but is likely to be formed with a short lifetime (<50 ns) and with a triplet energy <250 kJ/mol as the drug is an efficient quencher of the fenbufen triplet and the biphenyl triplet, and forms (1)O(2) by laser flash photolysis ((PQ)Phi(Delta)=0.025). Primaquine (PQ) exists as the monocation (PQH(+)) in aqueous solution at physiological pH. PQH(+) photoionises by a biphotonic process and also forms the monoprotonated cation radical (PQH(2+)*) by one electron oxidation by HO* (k(q)=6.6 x 10(9) M(-1) s(-1)) and Br*(2)(-) (k(q)=4.7 x 10(9) M(-1) s(-1)) at physiological pH, detected as a long-lived transient decaying essentially by a second order process (k(2)=7.4 x 10(8) M(-1) s(-1)). PQH(2+)* is scavenged by O(2), although at a limited rate (k(q)=1.0 x 10(6) M(-1) s(-1)). The reduction potential (E degrees) of PQH(2+)*/PQH(+) is < +1015 mV, as measured versus tryptophan (TRP*/TRPH). Primaquine also forms PQH(2+)* at pH 2.4, by one electron oxidation by Br*(2)(-) and proton loss (k(q)=2.7 x 10(9) M(-1) s(-1)). The non-protonated cation radical (PQ(+)*) is formed during one electron oxidation with Br*(2)(-) at alkaline conditions (k(q)=4.2 x 10(9) M(-1) s(-1) at pH 10.8). The estimated pK(a)-value of PQH(2+)*/PQ(+)* is pK(a) approximately 7-8. Primaquine is not a scavenger of O*(2)(-) at physiological pH. Thus self-sensitization by O*(2)(-) is eliminated as a degradation pathway in the photochemical reactions. Impurities in the raw material and photochemical degradation products initiate photosensitized degradation of primaquine in deuterium oxide, prevented by addition of the (1)O(2) quencher sodium azide. Photosensitized degradation by formation of (1)O(2) is thus important for the initial photochemical decomposition of primaquine, which also proceeds by free radical reactions. Formation of PQH(2+)* is expected to play an essential part in the photochemical degradation process in a neutral, aqueous medium.

Light Intensity Effects on Photoinduced Charge Separation Parameters in a Molecular Triad Based on an Iridium(III) Bis(terpyridine) Unit

The effect of photon flux on the yield and lifetime of charge separation over the extreme components of a D-Ir-A triad, where D is a triphenyl amine electron donor, A is a naphthalene bis(imide) electron acceptor and Ir is an Ir(III) bis(terpyridine) complex, has been investigated. In usual laboratory conditions, with nanosecond and picosecond laser pulses in the 4-8 mJ range, biphotonic processes take place. Biphotonic products and their evolution can introduce complications in reaction mechanisms and their interpretation but can also drastically reduce the yield and the lifetime of the charge-separated state. In the present case, after discussion of several possible mechanisms, the process detrimental to charge separation is ascribed to absorption of a photon by the photogenerated charge-separated state D(+)-Ir-A(-).

Energy transfer processes in (Er 3+–Yb 3+)-codoped germanate glasses for mid-infrared and up-conversion applications

Luminescence characteristics of Er 3+ -activated, Yb 3+ -sensitised GeO 2 –Na 2 O–Nb 2 O 5 heavy metal germanate glasses have been investigated in the context of searching active media for laser devices. Optical absorption, emission spectra and decay time measurements have been performed at room temperature on these materials. Intense 1540 nm infrared fluorescence and visible emission bands at 533, 554, and 660 nm were observed under continuous wave excitation at 980 nm. An efficient energy transfer from Yb 3+ to Er 3+ ions, increasing as a function of Yb 3+ concentration, favours the Er 3+ 1.54 μm eye-safe laser emission in these materials. The power dependence study of the upconverted emissions gives evidence of a bi-photonic process. Moreover, the Yb 3+ codoping enhances the up-conversion efficiency. Decay time measurements have been examined in the purpose of elucidating the possible mechanisms involved in this process. The experimental results are in good agreement with an effective Yb 3+ -to-Er 3+ nonradiative energy transfer.

Formation and reactivity of free radicals in 5-hydroxymethyl-2-furaldehyde – the effect on isoprenaline photostability

Solutions of glucose are used as diluents for drugs in various drug infusions. When sterilized by heat small amounts of the substance 5-hydroxymethyl-2-furaldehyde (5-HMF) is produced from glucose. At a hospital ward such infusions may be exposed to irradiation; including UV-light. The photoreactivity of the furaldehyde is investigated. It is shown to photodestabilize the catecholamine isoprenaline. It is shown to be a producer, but also a consumer, of singlet oxygen. The excited triplet, cation and anion radical have been produced by pulse radiolysis and flash photolysis and their absorbance characteristics have been determined. The triplet absorption spectrum showed absorption bands at 320 and 430 nm with molar absorption coefficients of 4700 and 2600 M-1 cm-1, respectively. The anion radical showed absorption bands at 330 and 420 nm with molar absorption coefficients of 2000 and 300 M-1 cm-1, respectively. The cation radical had an absorption band at 320 nm with a molar absorption coefficient of 5000 M-1 cm-1. The quantum yield for the production of singlet oxygen, sensitized by the 5-HMF triplet, was determined to be 0.6, whilst the quantum yield for the triplet formation was 1.0. Aqueous solutions of 5-HMF were found to photoionize to yield the hydrated electron and the cation radical of 5-HMF in a biphotonic process. The influences of pH, buffer and glucose on the formation of transients were evaluated. The reactions between 5-HMF and the solvated electron, the hydroxyl radical and the superoxide were also studied.

Photodissociation and photoionization mechanisms of 2,2’- and 4,4’-biphenyldiols: a laser flash photolysis study

Nanosecond and picosecond laser flash photolysis (LFP) of 2,2’- and 4,4’-biphenyldiols has been investigated in aqueous acidic and alkaline solutions to understand the details of the photodissociation (PD) and photoionization (PI) mechanisms of the two diols. For 2,2’-biphenyldiol, the photodissociation and photoionization following the excitation using UV light (248 or 266 nm) is seen to be a bi-photonic process, whereas that of the 4,4’-biphenyldiol is seen to follow a monophotonic mechanism. A detailed analysis of the nanosecond and picosecond LFP results indicate that the PD/PI of 2,2’-biphenyldiol involves the participation of the triplet (T1) state of the molecule. For 4,4’-biphenyldiol, however, the PD/PI occurs from the excited singlet (S1) state. It is inferred that the difference in the PD/PI behavior of 2,2’- and 4,4’-biphenyldiols arises due to the presence and absence of intramolecular hydrogen bonding in the two respective molecules. Qualitative potential energy diagrams have been presented to rationalize how the presence and absence of intramolecular hydrogen bonding causes a difference in the stabilization of the electronic states in the two diols and that ultimately determines the possibility of the bi-photonic mono-photonic PD/PI mechanisms for 2,2’- and 4,4’-biphenyldiols, respectively.