Advances in the synthesis of three-dimensional molecular architectures by dearomatizing photocycloadditions

An imidazoacridine-based TADF material as an effective organic photosensitizer for visible-light-promoted [2 + 2] cycloaddition

“…7 kcal mol À1 ), none have been previously explored as a triplet photosensitizer in [2 + 2] cycloaddition reactions. 11,42 We found that 3DPA2FBN, 4CzIPN and 3CZClIPN all promoted the cycloaddition of 3 to 4 albeit with lower conversion (entries [15][16][17]. Finally, the use of a metal-based photosensitizer [Ir(dF(Me)ppy) 2 (dtbbpy)]PF 6 (E T ¼ 62.9 kcal mol À1 ) 42 gave quantitative conversion of 3 to 4 (entry 18).…”

“…Given that the TADF materials presented in Table 1 possess similar triplet state lifetimes, 34 the high performance of ACR-IMAC may suggest a higher ISC rate compared to the others. 11,32 With the identication of ACR-IMAC as an effective photosensitizer, its general use for [2 + 2] cycloaddition was investigated. Dearomative and non-dearomative intramolecular [2 + 2] cycloadditions were examined in the presence of catalytic amounts of ACR-IMAC (Fig.…”

“…Given that the TADF materials presented in Table 1 possess similar triplet state lifetimes, 34 the high performance of ACR-IMAC may suggest a higher ISC rate compared to the others. 11,32…”

“…Three main criteria must be met for an EnT process to be efficient: (i) the triplet energy of the photosensitizer (PS) must be higher than that of the energy acceptor/substrate; (ii) the photosensitizer must have a high intersystem crossing (ISC) rate that induces a spin inversion; (iii) the photosensitizer must possess a long triplet excited-state lifetime. 11 The proposed mechanism for [2 + 2] photocycloaddition through an EnT process is described in Fig. 1 .…”

“…PCs based on more earth-abundant, rst-row transition metals have been recently explored, addressing some of these concerns. [11][12][13] Metal-free organic PCs, however, have become increasingly attractive alternatives, with many examples of strongly reducing or oxidizing PCs reported to date. [14][15][16][17][18][19][20] Several approaches have been taken to increase the rate of ISC in these materials, including functionalization with heavy halogens, or the use of carbonyl-based PCs such as p-extended benzophenones.…”