Supramolecular Structures for Photochemical Energy Conversion

Gust, Devens; Moore, Thomas A.; Moore, Ana L.

doi:10.2172/813606

Cited by 2 publications

(3 citation statements)

References 7 publications

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“…Recently, molecular systems in which the electron donor and electron acceptor are covalently connected have been investigated. − The intramolecular through-bond charge separation process usually takes place via the excited singlet states of the sensitizing electron donor dye and/or electron acceptor dye. In general, intramolecular charge separation rates are quite faster than the intermolecular electron transfer rates via the excited triplet state. , However, the lifetimes of the charge separation states of such dyads are not long enough to mediate the electron and/or hole of the charge separation state to electron carriers and to catalysts.…”

Section: Introductionmentioning

confidence: 99%

Photoinduced Charge Separation and Charge Recombination of Oligothiophene−Viologen Dyads in Polar Solvent

et al. 2004

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Photoinduced intramolecular charge separation and charge recombination of oligothiophene−methyl viologen dyads (T n −MV2+·2X-, n = 4 or 8, X- = I- or PF6 -), which were designed to generate positively charged radical ion pairs (T n •+−MV•+·2X-), have been investigated by the time-resolved fluorescence and transient absorption spectra in CH3CN. Upon excitation of the T8 moiety in T8−MV2+·2X-, the radical cation pair (T8 •+−MV•+·2X-) was produced via the excited singlet state of T8 (1T8*), because the fluorescence lifetime of the 1T8* moiety in T8−MV2+·2X- becomes short compared with pristine 1T8*. The lifetimes of T8 •+−MV•+·2X- were evaluated to be 720−980 ns depending on the counteranion, I- or PF6 -. On the other hand, T4−MV2+·2X- leads to lifetimes of T4 •+−MV•+·2X- of 210−240 ns, although the charge separation seems to occur via the excited triplet state of T4 (3T4*), because the fluorescence quenching of the 1T4* moiety in T4−MV2+·2X- was not observed. As factors to achieve these relatively long lifetimes of T n •+−MV•+·2X-, the charge recombination between of the positive charges (holes) on the T n and MV moieties and the center-to-center distance between the positive charges (holes) on the T n and MV moieties may be considered, in addition to the triplet spin character of T n •+−MV•+·2X-.

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Section: Introductionmentioning

confidence: 99%

Photoinduced Charge Separation and Charge Recombination of Oligothiophene−Viologen Dyads in Polar Solvent

et al. 2004

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“…Based on thermodynamic criteria, a comparison of the energies of paths a, b, and c in Scheme 5 immediately excludes the HT path, because it is 16.5 kcal mol À1 uphill. At first, one may guess that the H À T (path b:À26.1 kcal mol À1 ) must be a favorable process because of the exothermicity of the overall H À T. However, many previous studies indicated that this is most likely not the case especially when competing with an ET (path c: 6.8 kcal mol À1 ) in the reaction system, due to the extremely higher intrinsic barrier for H À T (Brinkley and Roth, 2005;Eberson, 1982;Gust et al, 1993;Li and Zhu, 2018). The energy requirement for ET to occur in N-Ph-THIQ oxidation by DDQ (DG ET = 6.8 kcal mol À1 ) can be well filled up by the highly exothermic follow-up hydrogen release from its radical cation (step d, DH HT = À31.8 kcal mol À1 ).…”

Section: Oxidation By Hydride Acceptorsmentioning

confidence: 99%

“…When a hydride acceptor serves as the oxidant, it was found that cleavage of the amine a-C-H bond could possibly be initiated either by hydride, hydrogen, or by electron transfer. Among them, the intrinsic barrier of electron transfer is known to be much lower than those of atom/group transfers (Brinkley et al, 2005;Fukuzumi, 2003;Gust et al, 1993;Li and Zhu, 2018). Therefore, even an uphill ET can be expected to occur if the energetic barrier is not much greater than 0.5 eV (1 eV = 23.1 kcal mol À1 ), because the deficiency of driving forces could be easily compensated by exothermic follow-up processes (Cheng et al, 1998;Eberson, 1982).…”

Section: Oxidation By Hydride Acceptorsmentioning

confidence: 99%

Toward Rational Understandings of α-C–H Functionalization: Energetic Studies of Representative Tertiary Amines

2020

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Functionalization of a-C-H bonds of tertiary amines to build various a-C-X bonds has become a mainstream in synthetic chemistry nowadays. However, due to lack of fundamental knowledge on a-C-H bond strength as an energetic guideline, rational exploration of new synthetic methodologies remains a far-reaching anticipation. Herein, we report a unique hydricity-based approach to establish the first integrated energetic scale covering both the homolytic and heterolytic energies of a-C-H bonds for 45 representative tertiary amines and their radical cations. As showcased from the studies on tetrahydroisoquinolines (THIQs) by virtue of their thermodynamic criteria, the feasibility and mechanisms of THIQ oxidation were deduced, which, indeed, were found to correspond well with experimental observations. This integrated scale provides a good example to relate bond energetics with mechanisms and thermodynamic reactivity of amine a-C-H functionalization and hence, may be referenced for analyzing similar structure-property problems for various substrates.

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Supramolecular Structures for Photochemical Energy Conversion

Cited by 2 publications

References 7 publications

Photoinduced Charge Separation and Charge Recombination of Oligothiophene−Viologen Dyads in Polar Solvent

Photoinduced Charge Separation and Charge Recombination of Oligothiophene−Viologen Dyads in Polar Solvent

Toward Rational Understandings of α-C–H Functionalization: Energetic Studies of Representative Tertiary Amines

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