Positive Photocatalysis of a Diels−Alder Reaction by Quenching of Excited Naphthalene−Indole Charge-Transfer Complex with Cyclohexadiene

Abstract

[reaction: see text] Naphthalene photo-catalyzes formation of cyclohexadiene-indole cycloadducts in a wavelength-dependent process. Steady-state irradiation and time-resolved fluorescence studies agree well with NP-InH ground-state charge transfer (CT) complexes as the key species responsible for the photo-catalyzed process.

Cucurbit[8]uril Mediated Donor–Acceptor Ternary Complexes: A Model System for Studying Charge-Transfer Interactions

“…Among the supramolocular binding forces, charge-transfer (CT) interactions can be considered the most controversial as they are likely the most easily identifiable interaction mode on account of characteristic features in electronic spectra, while their energetic contribution to the complex formation is often debatable. As CT effects are inherently quantum mechanical in nature, their experimental investigation and theoretical description remain challenging. − Commonly, a simplified but still widely accepted model by Mulliken is utilized to explain the CT process, albeit the need for more sophisticated theoretical descriptions that incorporate relaxation effects have arisen in the past decade. , A deep understanding of CT interactions is not only accompanied by theoretical advances but will subsequently benefit the design of systems that rely on physical charge separation (and subsequent migration) as in conducting polymers, in solar cells, for data storage applications, as well as in mimicry of nature’s photosynthesis machinery. − Furthermore, CT binding forces have also been exploited for the synthesis of novel materials. − While the majority of biological and artificial host–guest/receptor–substrate interactions can be understood in terms of electrostatic and polarization contributions, H-bonding, and solvation effects, − some enzymatic catalysis pathways, however, crucially rely on CT interaction. − Synthetic chemical transformations that depend on CT excitations have also been described. − …”

Catalytic processes activated by light

“…The species responsible for the catalysed process may not only be singlet and triplet excited states, but i) excited charge-transfer (CT) complexes (Scheme 4), 14 ii) exciplexes (Scheme 5), 15 iii) electron-transfer states of donor-acceptor (D-A) linked molecules (Scheme 6), 8 iv) electron-hole pairs (e À /h +. , Scheme 7), 13 and even v) metastable species (see above).…”

Visible-light driven acetoxylation and dioxygenation of indoles via electron donor–acceptor complexes

“…Indoles are very good electron donors for the formation of EDA complexes that have been explored for some catalystfree visible light-mediated reactions. [5][6][7][8][9][10] In parallel, hypervalent iodine reagents are also previously known for the formation of EDA complexes that have enabled their thermal reactions. 11,12 A few reports of the photochemical reactions of their EDA complexes have also been reported.…”