Diethylamino hydroxybenzoyl hexyl benzoate (DHHB)

Degradation of organic ultraviolet filter diethylamino hydroxybenzoyl hexyl benzoate in aqueous solution by UV/H2O2

Steady-state and transient-state photolysis experiments were conducted to investigate the degradation of organic ultraviolet filter diethylamino hydroxybenzoyl hexyl benzoate (DHHB) in the aqueous solution by UV/H2O2. Results showed that the obvious degradation of DHHB was not observed under UV irradiation (λ = 254 nm), and the DHHB degradation was conducted due to the oxidation by hydroxyl radical (HO·). While the H2O2 concentration was between 0.05 and 0.10 mol L(-1), the highest DHHB degradation efficiency was obtained. The lower solution pH favored the transformation of DHHB, and the coexisting Cl(-) and NO3(-) ions slightly enhanced the conversion. The degradation of DHHB by HO· followed a pseudo-first-order kinetic model with different initial DHHB concentrations. By intermediate products during DHHB oxidation and laser flash photolysis spectra analysis, a primary degradation pathway was proposed.

Influence of the Solvent Environment on the Ultrafast Relaxation Pathways of a Sunscreen Molecule Diethylamino Hydroxybenzoyl Hexyl Benzoate

The excited-state dynamics of photoexcited diethylamino hydroxybenzoyl hexyl benzoate (DHHB), a UVA absorber widely used in sunscreen formulations, are studied with transient electronic and vibrational absorption spectroscopy methods in four different solvents. In the polar solvents methanol, dimethyl sulfoxide (DMSO), and acetonitrile, strong stimulated emission (SE) is observed at early time delays after photoexcitation at a near-UV wavelength of λ_ex = 360 nm, and decays with time constants of 420 fs in methanol and 770 fs in DMSO. The majority (?95%) of photoexcited DHHB returns to the ground state with time constants of 15 ps in methanol and 25 ps in DMSO. In the nonpolar solvent cyclohexane, ? 98% of DHHB photoexcited at λ_ex = 345 nm relaxes to the ground state with a ? 10 ps time constant, and the SE is weak. DHHB preferentially adopts an enol form in its ground S₀ state, but excited state absorption (ESA) bands seen in TEAS are assigned to both the S₁-keto and S₁-enol forms, indicating a role for ultrafast intramolecular excited state hydrogen transfer (ESHT). This ESHT is inhibited by polar solvents. The two S₁ tautomers decay with similar time scales to the observed recovery of ground state population. For molecules that avoid ESHT, torsion around a central C-C bond minimizes the S₁-enol energy, quenches the SE, and is proposed to lead to a conical intersection with the S₀ state that mediates the ground state recovery. A competing trans-enol isomeric photoproduct is observed as a minor competitor to parent recovery in polar solvents. Evidence is presented for triplet (T₁) enol production in polar solvents, and for T₁ quenching by octocrylene, a common UVB absorber sunscreen additive. The T₁ keto form is observed in cyclohexane solution.

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 F?rster 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).

Coexistence effect of UVA absorbers to increase their solubility and stability of supersaturation

Objective: Sunscreens containing UVA absorbers in high concentrations are expected to be developed, since recent studies have suggested the possibility of involvement of UVA ray in skin cancer and early skin aging. Solubility and stability of supersaturation of UVA absorbers in UVB absorber were determined in the absence and the presence of cosmetic oil. Coexistence effect of UVA absorbers was analyzed to dissolve them in high concentrations.
Methods: Two UVA absorbers, diethylamino hydroxybenzoyl hexyl benzoate (DHHB) and butyl methoxydibenzoylmethane (BMDM), a UVB absorber, 2-ethylhexyl methoxycinnamate (EHMC), and a cosmetic oil, 2-ethylhexyl ester of oligomer of hydroxystearic acid (EH-O-HSA), were used. Their solutions were prepared at 80°C and cooled to 5°C. The solid DHHB and/or BMDM were added to it, and the time evolution of concentrations of the UVA absorbers in the solution phase was monitored.
Results: At the saturation in the absence of EH-O-HSA at 5°C, weight ratio of DHHB and BMDM to EHMC was 0.39/1.00 and 0.22/1.00, respectively. Addition of EH-O-HSA slightly changed the solubility of DHHB and BMDM. When the weight ratio of EH-O-HSA to EHMC was 0.20/1.00, weight ratio of DHHB and BMDM to EHMC was 0.35/1.00 and 0.25/1.00, respectively at the saturation at 5°C. In the presence of EH-O-HSA, a strong coexistence effect of DHHB and BMDM was found on their solubility. A thermodynamically stable saturated solution at 5°C having the composition that DHHB: BMDM: EHMC: EH-O-HSA = 0.47: 0.46: 1.00: 0.20 was obtained by the simultaneous addition of solid DHHB and BMDM into the initial solution.
Conclusion: The solution type composite having the highest concentrations of DHHB and BMDM prepared in this study exhibited critical wavelength at 368 nm that was just below the border for sunscreens being qualified as 'Broad Spectrum' protection under the new rule launched by US FDA.

Solvent Effects on Ultrafast Photochemical Pathways

Photochemical reactions are increasingly being used for chemical and materials synthesis, for example, in photoredox catalysis, and generally involve photoexcitation of molecular chromophores dissolved in a liquid solvent. The choice of solvent influences the outcomes of the photochemistry because solute-solvent interactions modify the energies of and crossings between electronic states of the chromophores, and they affect the evolving structures of the photoexcited molecules. Ultrafast laser spectroscopy methods with femtosecond to picosecond time resolution can resolve the dynamics of these photoexcited molecules as they undergo structural and electronic changes, relax back to the ground state, dissipate their excess internal energy to the surrounding solvent, or undergo photochemical reactions. In this Account, we illustrate how experimental studies using ultrafast lasers can reveal the influences that different solvents or cosolutes exert on the photoinduced nonadiabatic dynamics of internal conversion and intersystem crossing in nonradiative relaxation pathways. Although the environment surrounding a solute molecule is rapidly changing, with fluctuations in the coordination to neighboring solvent molecules occurring on femtosecond or picosecond time scales, we show that it is possible to photoexcite selectively only those molecular chromophores transiently experiencing specific solute-solvent interactions such as intermolecular hydrogen bonding.The effects of different solvation environments on the photodynamics are illustrated using four selected examples of photochemical processes in which the solvent has a marked effect on the outcomes. We first consider two aromatic carbonyl compounds, benzophenone and acetophenone, which are known to undergo fast intersystem crossing to populate the first excited triplet state on time scales of a few picoseconds. We show that the nonadiabatic excited-state dynamics are modified by transient hydrogen bonding of the carbonyl group to a protic solvent or by coordination to a metal cation cosolute. We then examine how different solvents modify the competition between two alternative relaxation pathways in a photoexcited UVA-sunscreen molecule, diethylamino hydroxybenzoyl hexyl benzoate (DHHB). This relaxation back to the ground electronic state is an essential part of the effective operation of the sunscreen compound, but the dynamics are sensitive to the surrounding environment. Finally, we consider how solvents of different polarity affect the energies and lifetimes of excited states with locally excited or charge-transfer character in heterocyclic organic compounds used as excited-state electron donors for photoredox catalysis. With these and other examples, we seek to develop a molecular level understanding of how the choice of solution environment might be used to control the outcomes of photochemical reactions.