Fused-Ring Derivatives of Quinoxalines: Spectroscopic Characterization and Photoinduced Processes Investigated by EPR Spin Trapping Technique

Abstract

10-Ethyl-7-oxo-7,10-dihydropyrido[2,3-f]quinoxaline derivatives, synthesized as promising biologically/photobiologically active compounds were characterized by UV/vis, FT-IR and fluorescent spectroscopy. Photoinduced processes of these derivatives were studied by EPR spectroscopy, monitoring in situ the generation of reactive intermediates upon UVA (λ max = 365 nm) irradiation. The formation of reactive oxygen species and further oxygen-and carbon-centered radical intermediates was detected and possible reaction routes were suggested. To quantify the investigated processes, the quantum yields of the superoxide radical anion spin-adduct and 4-oxo-2,2,6,6-tetramethylpiperidine N-oxyl generation were determined, reflecting the activation of molecular oxygen by the excited state of the quinoxaline derivative.

Copper(II) Thiosemicarbazone Complexes and Their Proligands upon UVA Irradiation: An EPR and Spectrophotometric Steady-State Study

“…Such photoinduced processes are often related to the generation of reactive oxygen species via the activation of molecular oxygen by the excited states of the photoactive molecule or directly by the molecular changes in the compound itself [ 50 , 51 ]. Previously, we studied in detail the photoactivation of molecular oxygen upon excitation of different quinolone derivatives (fluoroquinolones, nitroquinolones, selenadiazoloquinolones), and considerable photobiological effects were found for several derivatives [ 52 , 53 , 54 , 55 ].…”

A Strategy to Design a Donor–π–Acceptor Polymeric Hole Conductor for an Efficient Perovskite Solar Cell

“…Herein, we report a strategy for designing a D–π–A conducting polymeric HTM based on benzothiadiazole ( B ) acceptor and thiophene ( T ) donor units for the preparation of an efficient perovskite solar cell (Figure c). Among the many electron accepting units tested thus far, including B , quinoxaline ( Q ), DPP , or benzothiazole ( BT ), B and Q have moderate electron accepting abilities. TB and TQ (e.g., –D–A–D–A–) are some of the simplest structures and have been employed in bulk heterojunction organic solar cells to yield η = 5.3%–5.9% for the inverted or the conventional structures; however, the HOMO energy level of TB is −5.4 eV, slightly higher than that of TQ (−5.7 eV) .…”

“…Among the many electron accepting units tested thus far, including B , [ 34,35 ] quinoxaline ( Q ), [ 36 ] DPP , [ 25 ] or benzothiazole ( BT ), [ 37 ] B and Q have moderate electron accepting abilities. TB and TQ (e.g., -D-A-D-A-) are some of the simplest structures and have been employed in bulk heterojunction organic solar cells to yield η = 5.3%-5.9% for the inverted or the conventional structures; [ 38,39 ] however, the HOMO energy level of TB is −5.4 eV, [ 36 ] slightly higher than that of TQ (−5.7 eV). [ 39 ] TB , however, cannot be used in a perovskite solar cell because its HOMO is lower than the HOMO Perovskite (−5.3 eV) [ 40 ] (Figure 1 a).…”

Differentiation between Enamines and Tautomerizable Imines Oxidation Reaction Mechanism using Electron-Vibration-Vibration Two Dimensional Infrared Spectroscopy

“…Since the intermediates are highly reactive and have short lifetimes, it is difficult, in general, to isolate and investigate them. The techniques commonly employed for this purpose include UV/Vis [ 1 , 2 ], infrared (IR) [ 3 , 4 , 5 , 6 , 7 ], electron paramagnetic resonance (EPR) [ 8 , 9 , 10 , 11 ] as well as nuclear magnetic resonance (NMR) spectroscopy [ 12 , 13 ]. Among these techniques, infrared (IR) spectroscopy is one of the most convenient tools.…”