The excited-state dynamics of the radical anions of cyanoanthracenes

Abstract

The radical anion of 9,10-dicyanoanthracene (DCA) has been suggested to be a promising chromophore for photoredox chemistry, due to its nanosecond excited-state lifetime determined from indirect measurements. Here, we investigate...

Red Light-Based Dual Photoredox Strategy Resembling the Z-Scheme of Natural Photosynthesis

“…While earlier studies reported a lifetime in the range of several nanoseconds for 2* DCA •– , 138 , 139 this was questioned later, and in particular the luminescence of 2* DCA •– was doubted. Lifetimes on the picosecond timescale seem more realistic for 2* DCA •– , 101 , 140 − 142 in line with the excited-state lifetimes reported for other radical anions. 97 , 102 , 143 − 145 Furthermore, concerning the reactivity and stability of DCA •– , a variety of very different observations were reported in the literature, including claims of reasonably good stability of DCA •– , 146 as well as observations of comparatively rapid degradation reactions with the solvent, reaction intermediates or oxygen.…”

“…Gray circles mark the elementary reaction steps of (I) TTET, (II) reductive quenching of 3* DCA by DiPEA, and (III) substrate activation after excitation of DCA •– . The doublet excited state of that radical anion is extremely short-lived, 101 and therefore, 2* DCA •– is set in quotation marks, to emphasize the possibility that the photoreaction could in fact predominantly occur from preaggregated DCA •– /substrate encounter complexes, or could even involve some DCA photodegradation products.…”

“…This observation seems in good agreement with the estimated excited-state reduction potential of −2.6 V vs SCE for 2* DCA •– (see the Supporting Information, Section 4.3.4 for details). 101 …”

Photophysics of Perylene Diimide Dianions and Their Application in Photoredox Catalysis

“…On a conceptual level, the approach of our study is illustrated by Figure 5. As noted in the introduction, radical monoanions of perylene diimides and related compounds can be generated photochemically or electrochemically by single electron transfer (SET), leading to highly reducing species with very short excited‐state lifetimes (Figure 5 a, left) [5–7, 22, 43, 46] . Alternatively, closed‐shell monoanions with longer‐lived excited states that are also very reducing have been produced by deprotonation of suitable pre‐catalysts with bases (Figure 5 a, right) [16b] .…”

“…As noted in the introduction, radical monoanions of perylene diimides and related compounds can be generated photochemically or electrochemically by single electron transfer (SET), leading to highly reducing species with very short excited‐state lifetimes (Figure 5 a , left). [ 5 , 6 , 7 , 22 , 43 , 46 ] Alternatively, closed‐shell monoanions with longer‐lived excited states that are also very reducing have been produced by deprotonation of suitable pre‐catalysts with bases (Figure 5 a , right). [16b] Our work adds the concept of two‐electron transfer (“2‐ET” in Figure 5 b ) to convert a pre‐catalyst into a closed‐shell dianion with high reducing power and comparatively long excited‐state lifetime.…”