Microwaves in Photochemistry and Photocatalysis

Cı́rkva, Vladimı́r

doi:10.1002/9783527651313.ch14

Cited by 3 publications

(6 citation statements)

References 147 publications

(113 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The very first synthesis of [6]helicene was accomplished via a 12-step route in 1956 . Since then, a number of methods for helicene synthesis have been introduced. − Among other approaches, the photochemical method (i.e., oxidative photocyclization) seems to be the most flexible and therefore the most used in helicene chemistry up to now. ,,− The original synthesis established by Mallory is based on the UV-light induced cis/trans photoisomerization of a stilbene derivative followed by a symmetry-allowed conrotatory electrocyclization of the cis isomer to generate the trans -dihydrophenanthrene derivative as an intermediate. In the presence of air and a catalytic amount of iodine, the intermediate is immediately converted by dehydrogenation into a fully aromatic compound.…”

Section: Introductionmentioning

confidence: 99%

“…The improved photochemical methods employed propylene oxide, cyclohexene, or THF, for example, to act as scavengers of forming hydroiodic acid. Recently, the air-driven potassium iodide-mediated oxidative photocyclization of stilbenes has been reported, and electrodeless discharge lamps as a novel light source in a microwave reactor have been introduced. , …”

Section: Introductionmentioning

confidence: 99%

“…Recently, the air-driven potassium iodide-mediated oxidative photocyclization of stilbenes has been reported, 26 and electrodeless discharge lamps as a novel light source in a microwave reactor have been introduced. 22,23 The elimination method of hydrogen fluoride called photocyclodehydrofluorination for the synthesis of partially fluorinated PAHs from corresponding fluorinated stilbenes has recently been described. 25 The introduction of fluorine substituents into helicene skeletons is a prospective strategy for tuning the properties required for application in organic electronic devices.…”

Section: ■ Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Preparation and Physicochemical Properties of [6]Helicenes Fluorinated at Terminal Rings

Cı́rkva¹,

Jakubík²,

Strašák³

et al. 2019

J. Org. Chem.

Self Cite

View full text Add to dashboard Cite

The first racemization-stable helicene derivatives fluorinated at terminal rings, 1,2,3,4-tetrafluoro[6]helicene (6) and 1,2,3,4,13,14,15,16-octafluoro[6]helicene (15), were synthesized via the Wittig reaction followed by oxidative photocyclization in an overall yield of 41% of 6 and 76% of 15. The changed electronic structure in fluorinated helicenes was reflected in a slight shift of UV–vis absorption, fluorescence excitation, and emission spectra maxima when compared to unsubstituted [6]helicene. Cyclic voltammetry revealed a moderate decrease in the HOMO–LUMO gap with increasing fluorination. The specific rotation of tetrafluoro[6]helicene 6 enantiomers was found to be approximately 25% lower than that of unsubstituted [6]helicene. The theoretical study of the racemization barrier suggested a reasonable shift toward higher energy with increasing fluorination. The increasing fluorination also significantly affected the intermolecular interactions in the crystal lattice. The observed CH···F interactions led to the formation of 1D-molecular chains in the crystal structures of both fluorinated helicenes.

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Preparation and Physicochemical Properties of [6]Helicenes Fluorinated at Terminal Rings

Cı́rkva¹,

Jakubík²,

Strašák³

et al. 2019

J. Org. Chem.

Self Cite

View full text Add to dashboard Cite

show abstract

“…The noble gases Kr and Xe are environment-friendly, inert, and easily ionized gases, more so at low pressures than they are at higher pressures [12]. Their inertness makes them attractive substitutes in MDELs since they do not interfere with the lamp's operation.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, upon ionization, these gases generate excimer molecules that when excited emit UV light at different wavelengths. Excimer formation uses dielectric barrier discharge (DBD) to generate incoherent UV radiation as the light source for photophysical and photochemical reactions [12]. Despite the several studies regarding rare-gas dimeric excimers (e.g., Ar 2 *, Kr 2 * and Xe 2 *) [13][14][15] and rare-gas halide (RH*) excimers (e.g., KrCl*, XeCl*, XeBr*, XeI*), [16][17][18][19] only scant studies have highlighted their applicability in (microwave/UV)-induced photolytic decomposition of pollutants in contaminated wastewaters.…”

Section: Introductionmentioning

confidence: 99%

Development of a Hg-free UV light source incorporating a Kr/Br2 gas, and its application for wastewater treatments

Chitete-Mawenda

Serpone

Horikoshi

2021

Photochem Photobiol Sci

View full text Add to dashboard Cite

Mercury lamps are typically the major light sources in water treatments. However, the use of mercury has raised some concerns with regard to the Minamata Convention on Mercury. As such, Hg-free microwave discharged electrodeless lamps (MDELs) that incorporate a rare gas and a halogen gas (R/H-MDEL) have been investigated with such Hg-free mixture filler gases as Kr/Cl 2 , Xe/Cl 2 , and Kr/Br 2 (R/H). Of these, only the Kr/Br 2 -MDEL lamp is self-ignited at an inner pressure of 15 Torr when irradiated with microwave radiation. Accordingly, a novel Kr/Br 2 three-layer MDEL (Kr/Br 2 -MDEL) photoreactor was fabricated to assess the optimal gas composition and gas pressure toward its performance vis-à-vis the treatment of model wastewaters contaminated with the tartrazine dye in aqueous media and with Escherichia coli (E. coli) bacteria. The extent of degradation of the tartrazine dye and sterilization of E. coli increased with irradiation time, with microwave radiation power (100, 200, and 300 W), and with increased sample flow rate 0.4 L min -1 to 0.8 L min -1 . The tartrazine-contaminated wastewater was treated at a flow rate of 0.4 L min -1 for 60 min of microwave irradiation by three different protocols that resulted in UV (62%) >> UV/ROS (24%) > ROS (0%); ROS denotes reactive oxygen species. After 5 min irradiation of the E.coli wastewater, also at 0.4 L min -1 , the order was UV (99.5%) ≈ UV/ROS (99.3%) >> ROS (14.5%). For comparison, the photosterilization of E. coli with an equivalent Hg/Ar-MDEL light source was also nearly complete (99.7%). Thus, the suitability of the environmentally friendlier Kr/Br 2 gas fill to replace Hg/Ar filler gas in MDELs for the photoelimination of organic pollutants and microbial disinfection in aqueous media has been demonstrated.

show abstract

Application of Microwave Energy to Biomass: A Comprehensive Review of Microwave-Assisted Technologies, Optimization Parameters, and the Strengths and Weaknesses

Lozano Pérez,

Lozada Castro,

Guerrero Fajardo

2024

JMMP

View full text Add to dashboard Cite

This review article focuses on the application of microwave-assisted techniques in various processes, including microwave-assisted extraction, microwave-assisted pyrolysis, microwave-assisted acid hydrolysis, microwave-assisted organosolv, and microwave-assisted hydrothermal pretreatment. This article discusses the mechanisms behind these techniques and their potential for increasing yield, producing more selectivity, and lowering reaction times while reducing energy usage. It also highlights the advantages and disadvantages of each process and emphasizes the need for further research to scale the processes and optimize conditions for industrial applications. A specific case study is presented on the pretreatment of coffee waste, demonstrating how the choice of microwave-assisted processes can lead to different by-products depending on the initial composition of the biomass.

show abstract

Microwaves in Photochemistry and Photocatalysis

Cited by 3 publications

References 147 publications

Preparation and Physicochemical Properties of [6]Helicenes Fluorinated at Terminal Rings

Preparation and Physicochemical Properties of [6]Helicenes Fluorinated at Terminal Rings

Development of a Hg-free UV light source incorporating a Kr/Br2 gas, and its application for wastewater treatments

Application of Microwave Energy to Biomass: A Comprehensive Review of Microwave-Assisted Technologies, Optimization Parameters, and the Strengths and Weaknesses

Contact Info

Product

Resources

About