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“…In fact, it has been previously reported that electron transfer in a block copolymer donor−(acceptor or donor)−acceptor copolymer takes place when the appropriate chromophores are attached to a semirigid polynorbornene backbone and where the central donor (or acceptor) block was excited . In low molecular weight donor−donor−acceptor triads, two-electron-transfer steps ,,− that are sometimes reversible have been observed …”
Section: Introductionmentioning
confidence: 99%
“…In fact, it has been previously reported that electron transfer in a block copolymer donor-(acceptor or donor)-acceptor copolymer takes place when the appropriate chromophores are attached to a semirigid polynorbornene backbone and where the central donor (or acceptor) block was excited. 5 In low molecular weight donordonor-acceptor triads, two-electron-transfer steps 1,2,[6][7][8][9] that are sometimes reversible have been observed. 1 For these materials to be useful as devices, it would be optimal to arrange the graded series of chromophores so that electron transfer is possible only in one direction and that energy-wasting processes such as competing singlet or triplet energy transfer and back electron transfer are suppressed.…”
Polynorbornenes substituted with 1-cyano-2-naphthyl and
2,5-dicyanophenyl groups as acceptors and terminated
with pyrene as donor have been prepared by ring-opening metathesis
polymerization. When excited with
monochromatic light, pyrene transfers an electron, producing a radical
ion pair with concurrent reduction of
the acceptor. In the copolymers with one acceptor block,
steady-state emission spectra reveal extensive pyrene
fluorescence quenching and exciplex formation between the pyrene and
the acceptor. In copolymers with
two acceptor blocks, the steady-state emission spectra reveal two
intramolecular exciplexes assigned to the
cyanonaphthalene−pyrene and dicyanobenzene−pyrene excited-state
complexes. Transient absorption spectra
display an overlap of the pyrene triplet−triplet and radical cation
spectra for all of the polymers. The lifetimes
of the transient absorption maxima are dependent upon the identity of
the acceptor and the length of the
acceptor block.
“…In fact, it has been previously reported that electron transfer in a block copolymer donor−(acceptor or donor)−acceptor copolymer takes place when the appropriate chromophores are attached to a semirigid polynorbornene backbone and where the central donor (or acceptor) block was excited . In low molecular weight donor−donor−acceptor triads, two-electron-transfer steps ,,− that are sometimes reversible have been observed …”
Section: Introductionmentioning
confidence: 99%
“…In fact, it has been previously reported that electron transfer in a block copolymer donor-(acceptor or donor)-acceptor copolymer takes place when the appropriate chromophores are attached to a semirigid polynorbornene backbone and where the central donor (or acceptor) block was excited. 5 In low molecular weight donordonor-acceptor triads, two-electron-transfer steps 1,2,[6][7][8][9] that are sometimes reversible have been observed. 1 For these materials to be useful as devices, it would be optimal to arrange the graded series of chromophores so that electron transfer is possible only in one direction and that energy-wasting processes such as competing singlet or triplet energy transfer and back electron transfer are suppressed.…”
Polynorbornenes substituted with 1-cyano-2-naphthyl and
2,5-dicyanophenyl groups as acceptors and terminated
with pyrene as donor have been prepared by ring-opening metathesis
polymerization. When excited with
monochromatic light, pyrene transfers an electron, producing a radical
ion pair with concurrent reduction of
the acceptor. In the copolymers with one acceptor block,
steady-state emission spectra reveal extensive pyrene
fluorescence quenching and exciplex formation between the pyrene and
the acceptor. In copolymers with
two acceptor blocks, the steady-state emission spectra reveal two
intramolecular exciplexes assigned to the
cyanonaphthalene−pyrene and dicyanobenzene−pyrene excited-state
complexes. Transient absorption spectra
display an overlap of the pyrene triplet−triplet and radical cation
spectra for all of the polymers. The lifetimes
of the transient absorption maxima are dependent upon the identity of
the acceptor and the length of the
acceptor block.
“…The long-wavelength band of the aniline chromophores is hidden under the much stronger acceptor transition at 314 nm. Although low-energy charge transfer states must exist in the dyads and triads, transitions to these states are not observed in the UV absorption spectra, probably due to a small transition probability. 2 Representative UV absorption spectra (cyclohexane): model donor D3 , model acceptor A0 , and triad TC3 .…”
Section: Resultsmentioning
confidence: 99%
“…The process of photoinduced charge separation via a sequence of short-range electron transfer steps as it occurs in natural photosynthesis has inspired many chemists to design molecular systems which may accomplish the same efficient and longlived charge separation. Some groups have used building blocks that resemble the chromophores of Nature, [1][2][3] and more or less attempt to mimic the photosynthetic apparatus, 4 while others have implemented multistep charge separation schemes in very differently constructed organic, [5][6][7][8][9][10][11][12][13][14] inorganic, [15][16][17] and supramolecular systems. [18][19][20] The overall efficiency in multistep charge separation sequences depends critically on the competition between forward charge separation steps and charge recombination processes.…”
Trifunctional electron donor-donor-acceptor molecules are described in which photoinduced charge separation, D 2 -D 1 -A* f D 2 -D 1 + -A -, is followed by a charge migration step D 2 -D 1 + -A -(CS1) f D 2 + -D 1 -A -(CS2), leading to a relatively long-lived charge-separated state. The rate of the charge migration process could be determined in a range of solvents of low polarity. In benzene and dioxane, reversibility of the process allowed the determination of the free energy difference between CS1 and CS2. The relative energy of the CS2 state is much lower than expected from simple electrostatic models. An increase of the charge migration rate was found with increasing solvent polarity within a series of alkyl ethers or alkyl acetates. However, an apparent preferential stabilization of the CS1 state in acetates relative to ethers leads to discontinuities in the solvatochromic shift behavior of the CT fluorescence from the CS1 state, and in the increase of the charge migration rate as a function of dielectric constant. In a reference compound lacking the intermediate redox unit, direct long-range charge separation yielding a D 2 + -bridge-A -charge-separated state can occur, but the yield is significantly lower than in the triads.
Six new donor‐bridge‐acceptor compounds have been synthesized which contain a long n‐tetradecyl chain attached to the donor or acceptor moiety, or to both of them. Systems 1, 2, and 3 are analogs of the fluorescent probe molecule Fluoroprobe (4). They contain a rigidly extended 4‐methylenepiperidine bridge and show relatively strong charge transfer fluorescence in solvents of low and medium polarity. Systems 1a, 2a, and 3a contain a semiflexible 4‐methylpiperidine bridge, obtained after hydrogenation of the exocyclic double bond of 1, 2 and 3, respectively. These systems undergo a conformational change following photoinduced charge separation (“harpooning”) in nonpolar solvents and probably also in solvents of medium polarity. Both the steady state fluorescence spectra and the fluorescence decay times of the extended charge transfer (ECT) species show that the photoinduced folding process is effectively slowed down by the introduction of the long alkyl tails. This is most pronounced for 1a which has an n‐tetradecyl group attached to both donor and acceptor. In solution a small difference in the rate of folding is observed between 2a and 3a, which have a single n‐tetradecyl chain attached to the acceptor only and to the donor only, respectively.
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