The Facile Generation of a Tetramethyleneethane Type Radical Cation and Biradical Utilizing a 3,4-Di(α-styryl)furan and a Photoinduced ET and Back ET Sequence

Abstract

Product analyses and nanosecond time-resolved spectroscopy on laser flash photolysis were studied for the photoinduced electron-transfer reaction of 3,4-di(alpha-styryl)furan (6a). A combination of these results, kinetic, density functional theoretical (DFT), and time-dependent DFT analyses enabled assignment of the absorption to the tetramethyleneethane (TME)-type radical cation (7a*+, lambda(max) = 392 nm) and the corresponding singlet biradical ((1)7a**, lambda(max) = 661 nm). These two intermediates were mechanistically linked to each other with a facile back electron-transfer reaction. The present studies provide a new method for the generation of aryl-substituted TME-type intermediates.

Density functional theory study of silole‐fused tetramethyleneethane biradicals with orbital interactions

“…HOMO– > LUMO transition of 1 7 •• contributes greatly to λ ET at 673 nm, while singly occupied molecular orbital (SOMO)(2)– > LUMO transition of 3 7 •• is the major contributor to λ ET at 450 nm, the source of the λ ET differences between 1 7 •• and 3 7 •• . On the other hand, λ ET of 1 3 •• is calculated to be 743 nm (Chart ), while that of 3 3 •• is not in the visible region . This is the reason why 3 3 •• was not observed in this region in the earlier LFP investigation with 2 for nanosecond time‐resolved absorption spectroscopy.…”

“…Because TDDFT calculations often give satisfactory approximations of λ ET to the observed λ AB of transient intermediates, it is expected that 1 7 •• and 3 7 •• will be observed distinguishably using the time‐resolved absorption spectroscopy on LFP.…”

“…From this perspective, Ikeda et al . devised a new method to generate TME 3 •• [Scheme (a)], which is the diphenyl derivative of the furan‐fused TME, that utilizes photoinduced electron‐transfer (PET) reaction of 3,4‐di( α ‐styryl)furan ( 2 ) with a photosensitizer (Sens) . This process was the first to apply the PET degenerate Cope rearrangement of 2,5‐diphenyl‐1,5‐hexadienes [ 4 , Scheme (b)] to TME chemistry.…”

“…Note that observation of the absorption in the visible region is informative for the characterization of the transient intermediates. The absorption maximum ( λ AB ) of 1 3 •• was observed at 661 nm (Chart ) by using nanosecond time‐resolved absorption spectroscopy on laser flash photolysis (LFP) . However, absorption by the triplet counterpart 3 3 •• was not observed in the visible region.…”

Multi‐Input/Multi‐Output Molecular Response System Based on the Dynamic Redox Behavior of 3,3,4,4‐Tetraaryldihydro[5]helicene Derivatives: Reversible Formation/Destruction of Chiral Fluorophore and Modulation of Chiroptical Properties by Solvent Polarity

“…A cosensitizing system that used an N-methylquinolinium tetrafluoroborate ([NMQ]A C H T U N G T R E N N U N G [BF 4 ], sensitizer, 1.0 mm)-toluene (cosensitizer, 1.0 m) couple in aerated MeCN at ambient temperature was used, since this system allows us to directly detect the intermediary cation radicals in a one-electron oxidation process (Scheme S1 in the Supporting Information). [26] Scheme 5. Mechanism of interconversion.…”