Aminoferrocene and ferrocene amino acid as electron donors in modular porphyrin-ferrocene and porphyrin-ferrocene-porphyrin conjugates

FULL PAPER

DOI:10.1002/ejic.201402138

Aminoferrocene and Ferrocene Amino Acid as Electron

Donors in Modular Porphyrin–Ferrocene and Porphyrin–

Ferrocene–Porphyrin Conjugates

Jascha Melomedov,^[a]Julian Robert Ochsmann,^[b]Michael Meister,^[b]

Frédéric Laquai,^[b]and Katja Heinze*^[a]

Keywords: Artificial photosynthesis / Energy transfer / Electron transfer / Metallocenes / Porphyrins

New amide-linked porphyrin–ferrocene conjugates [M(P^Ar)–

Fc] were prepared from aminoferrocene and a carboxy-sub-

stituted meso-tetraaryl-porphyrin [M = 2H, Zn; Ar = mesityl

(Mes), C₆F₅: 3a, 3e, Zn-3a, Zn-3e]. A further porphyrin build-

ing block was attached to the second cyclopentadienyl ring

of the ferrocene moiety to give the metallopeptides M(P^Mes)–

Fc–M(P^Ar) (M = 2H, Zn; Ar = C₆H₅, 4-C₆H₄F: 6b, 6c, Zn-6b,

Zn-6c). The effects of the Ar substituents, the porphyrin cen-

tral atom M and the presence of the second porphyrin at the

ferrocene hinge on the excited-state dynamics was studied

by optical absorption spectroscopy, electrochemistry, steady-

state emission, time-resolved fluorescence measurements

troscopy and electrochemical measurements. However, the

porphyrin emission is strongly quenched with respect to that

of the reference porphyrins without the ferrocene moieties.

Fluorescence is partially recovered at lower temperatures,

which suggests an activated excited-state decay process. All

excited-state lifetimes are reduced with respect to those of

the reference porphyrins. The quantum yields and lifetimes

correlate with the porphyrin and ferrocene redox potentials.

All observations point to photoinduced electron transfer from

ferrocene to the porphyrin in the normal Marcus region as

the dominant excited-state reactivity. The resulting charge-

separated states of selected conjugates were studied by ns–

and transient absorption pump–probe spectroscopy in ad- μs transient absorption pump–probe spectroscopy. Hints for

dition to density functional theory calculations. In the ground

state, only weak interactions were revealed between the fer-

rocene and porphyrin units by optical absorption spec-

the feasibility of singlet–singlet energy transfer between co-

facial porphyrins were found in tweezers 6 and Zn-6.

Many ferrocene derivatives are stable, feature well-de-

fined Fc/Fc⁺redox states and are able to reduce the S₁ex-

cited state of the porphyrin.^[4,5]This renders ferrocene

highly suitable as an electron donor in model compounds

for artificial charge separation and molecular electronic de-

vices.^[1,4,6,7]

Recently, we reported a modular synthetic strategy for

amide-linked architectures with porphyrin amino acids as

chromophores, quinones as electron acceptors and ferro-

cenes as electron donors. In these conjugates, both oxidative

photoinduced electron transfer (PET), that is, excited por-

phyrin to quinone, and reductive PET pathways, namely,

ferrocene to excited porphyrin, have been identified

(Scheme 1).^[1f]

The core building block of these artificial reaction

centres is a trans-AB₂C-substituted meso-tetraaryl por-

phyrin amino acid,^[9,10]and different aryl groups of varying

electron-donating or -withdrawing power at the meso posi-

tions dictate the preferred PET pathway. To specifically fo-

cus on the reductive pathway, new porphyrin–ferrocene

conjugates and porphyrin–ferrocene–porphyrin tweezers^[6]

with tuneable electronic properties of the porphyrin electron

acceptor as well as of the ferrocene electron donor have

been designed in the present study. Aminoferrocene^[5a]and

Introduction

To mimic the light-harvesting and charge-separating pro-

cesses in natural photosynthesis, a plethora of model com-

pounds have been designed and thoroughly investi-

gated.^[1–4,6]These artificial photosynthetic reaction centres

typically consist of electron-donor and electron-acceptor

units combined with a chromophore. Porphyrins and

metalloporphyrins are highly suited and well-established

building elements for biomimetic model compounds^[1–4,6]

owing to their favourable photophysical properties and

their outstanding role in plant and bacterial photosynthesis.

In artificial reaction centres, porphyrins can act as electron

donors^[2]or acceptors.^[3]Typically, porphyrins function as

electron acceptors in porphyrin–ferrocene arrays [M(P)–

Fc], and the organometallic ferrocene acts as an electron

donor.^[4,6]

[a] Institute of Inorganic Chemistry and Analytical Chemistry,

Johannes Gutenberg-University of Mainz,

Duesbergweg 10-14, 55128 Mainz, Germany

E-mail: katja.heinze@uni-mainz.de

http://ww w .ak-heinze.chemie.uni-mainz.de/

[b] Max Planck Institute for Polymer Research,

Ackermannweg 10, 55128 Mainz, Germany

Supporting information for this article is available on the

WWW under http://dx.doi.org/10.1002/ejic.201402138.

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Scheme 1. Artificial photosynthetic reaction centres assembled through amide bonds and based on trans-AB₂C-substituted porphyrin

amino acids, anthraquinone carboxylic acid and aminoferrocene.^[1f]

ferrocene amino acid (N-Fmoc-protected; Fmoc = 9-fluor- were employed to further underscore the experimental re-

enylmethoxycarbonyl)^[5a]were employed as electron donors sults.

with different redox potentials. Furthermore, the orthogo-

nal amine/acid substitution pattern of the latter allows

straightforward access to unsymmetric 1,1Ј-disubstituted

Results and Discussion

ferrocenes with two different porphyrins. We report the syn-

thesis of M(P^Ar)–Fc dyads [M = 2H, Zn; Ar = mesityl

The porphyrin starting materials and reference com-

(Mes), C₆F₅: 3a, 3e, Zn-3a, Zn-3e) by amide coupling of a pounds 1a, 2a, Zn-1a, 1e, 2e, 4b–4e, Ac-4b–Ac-4e, Zn-Ac-

porphyrin monoacid with aminoferrocene. N-Fmoc-pro- 4b and Zn-Ac-4c were prepared according to literature pro-

tected conjugates N-Fmoc–Fc–P^Ar(Ar = C₆H₅, 4-C₆H₄F, cedures.^[8,10]The synthesis and characterisation of reference

4-C₆H₄CF₃, C₆F₅: 5b–5e) were introduced as versatile porphyrin [10,20-bis(pentafluorophenyl)-5,15-bis(4-meth-

building blocks by coupling porphyrin amino acid esters oxycarbonylphenyl)porphyrinato]zinc(II) (Zn-1e) is de-

with N-Fmoc-protected ferrocene amino acid. Finally, bis- scribed in the Experimental Section. All analytical data are

(porphyrin) tweezers P^Mes–Fc–P^Ar(6b and 6c) are accessible collected in the Supporting Information.

from building blocks 5b and 5c and a porphyrin acid by

amide coupling. Metallation yields the corresponding zinc- and 3e were prepared in a two-step procedure from trans-

The new porphyrin–ferrocene (P^Ar–Fc) conjugates 3a

(II) porphyrins Zn(P^Mes)–Fc–Zn(P^Ar) (Zn-6b and Zn-6c). A₂B₂porphyrin diesters 1a/1e (Ar

=

Mes,^[1f,2d,8,10]

All new compounds were fully characterised by standard C₆F₅)^[1f,10]by partial hydrolysis to give monoacids 2a/2e,

techniques in addition to detailed photophysical and redox followed by in situ acid activation with thionyl chloride and

chemical characterisation. Density functional calculations coupling with aminoferrocene.^[5a]Metallation of the dyads

Scheme 2. Syntheses of 3 and Zn-3 from aminoferrocene.

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3 with zinc(II) acetate dihydrate gave the corresponding hydrofuran ([D₈]THF), two amide proton resonances were

ferrocenylzinc(II) porphyrins [Zn(P^Ar)–Fc] Zn-3a and Zn- found at δ ≈ 9.75 ppm for the FcNH amide proton and δ =

3e (Scheme 2).^[1f,9,10]

10.21–10.42 ppm for the P^ArNH amide proton, which sug-

The key building block of 1,1Ј-ferrocenylenebis(porphyr- gests that there are NH··O hydrogen bonds to the THF sol-

ins) 6 is the N-Fmoc-protected ferrocene amino acid.^[5a]It vent. Interestingly, all tweezers 6 display only a single amide

was convenient to first couple a porphyrin amino ester 4b– resonance at δϾ9 ppm in CDCl₃, which indicates that only

4e^[1f,9,10]to the C terminus of the central ferrocene unit to one NH group forms hydrogen bonds. This finding suggests

give N-Fmoc–Fc–P^Ar(Ar = C₆H₅, 4-C₆H₄F, 4-C₆H₄CF₃, that an intramolecular hydrogen bond (IHB) across the fer-

C₆F₅: 5b–5e). To prove the synthetic concept of adding a rocene moiety might be present in CDCl₃solution. Such

further porphyrin to 5, the N-Fmoc protecting groups of IHBs have been frequently observed for 1,1Ј-disubstituted

5b and 5c were removed with tris(2-aminoethyl)amine, and ferrocenes with amide arms in weakly coordinating sol-

finally the second porphyrin was attached to the N terminus vents.^[5]The IR spectra of Zn-6b in CH₂Cl₂were recorded,

after activation of the porphyrin acid 2a with 1-chloro- and indeed two NH absorption bands were found at 3430

N,N,2-trimethyl-1-propenylamine (Ghosez’s reagent),^[11]and 3299 cm^–1; these bands clearly indicate the simulta-

similar to the synthesis of conjugates 3 (Scheme 3). Again, neous presence of free and hydrogen-bonded NH groups,

metallation of 6b or 6c with zinc(II) acetate dihydrate respectively. The intramolecular nature of the hydrogen

yielded the corresponding trimetallic Zn–Fe–Zn complexes bond is shown by the retention of the NH_free/NH_bondedra-

Zn-6b and Zn-6c.^[1f,9,10]

tio as the samples are diluted (Figure 1, a). An optimised

The correct compositions of all of the new compounds 3, DFT model of Zn-6b (B3LYP, LANL2DZ, IEFPCM

Zn-3, 5, 6 and Zn-6 were established by multinuclear NMR CH₂Cl₂) is displayed in Figure 1 (b), and the proposed

spectroscopy (¹H, ¹³C and ¹⁹F), IR and UV/Vis spec- NH··O IHB is illustrated. This type of IHB with an eight-

troscopy, as well as (high-resolution) mass spectrometry. membered ring is the most stable one according to literature

The appearance of the amide proton resonances of 3, Zn-3 precedent for other amide substituents at the 1,1Ј-disubsti-

and 5 in CDCl₃at δ ≈ 9.20 ppm indicates the successful tuted ferrocene.^[5]The IHB results in a V-shape of the

formation of the amide bonds. For tweezers 6 in [D₈]tetra- tweezers (Figure 1, b).

Scheme 3. Syntheses of 5, 6 and Zn-6 from N-Fmoc-protected ferrocene amino acid.

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Figure 2. Cyclic voltammograms of 3a, Zn-3a, 1a and Zn-1a in

[nBu₄N][PF₆]/CH₂Cl₂.

0.14 V, as expected from the additional carbonyl substituent

at the ferrocene hinge (Figure 2, a and b).^[5b]

In tweezers 6 and Zn-6, the redox waves of both por-

phyrins and the ferrocene unit (E_1/2= 0.15–0.16 V) are su-

perimposed (Table 1). In all cases, reversible two-electron

Figure 1. (a) IR spectra of Zn-6b at high and low concentrations in

CH₂Cl₂at room temperature. (b) Calculated (B3LYP/LANL2DZ,

IEFPCM) V-shape structure of Zn-6b featuring an NH···O IHB

(CH hydrogen atoms omitted for clarity).

All cyclic voltammograms of dyads 3, Zn-3 and 5 exhibit waves are observed for the first oxidations of the por-

two reversible oxidation and two reversible reduction pro- phyrins. Zinc porphyrins Zn-6 show a further 2e oxidation

cesses of the porphyrin moieties and a reversible wave for wave, whereas this wave is split into two 1e waves for the

the ferrocene/ferrocenium couple. For instance, the cyclic free-base bis(porphyrins) 6. In the reductive region, free-

voltammograms of 3a, Zn-3a and the corresponding ferro- base conjugates 6 show a 2e and a further 1e wave, whereas

cene-free reference porphyrins 1a and Zn-1a are depicted in Zn-6 feature only a single 1e reduction under our condi-

Figure 2. Hence, the Fc–P conjugates 3, Zn-3 and 5 can tions. The Fc/Fc⁺potential remains essentially unaffected

store and release up to five electrons. With increasing elec- by the appendage of the second porphyrin to 5. Vice versa,

tron-withdrawing power of the meso-aryl substituents, an the influence of the ferrocene moiety on the redox features

anodic shift of the porphyrin redox potentials was detected of the porphyrin is marginal.^[1f]In essence, the redox prop-

for 3, 5 and Zn-3, as expected (Table 1).^[1f,10]The ferrocene/ erties are described by the properties of the individual

ferrocenium wave was detected at E_1/2≈ –0.09 V for 3 and building blocks, and the electronic interactions in the

Zn-3, whereas the oxidation of the ferrocene amino acid ground state between the building blocks of the dyads and

building block in 5 is shifted by ca. 230 mV to E_1/2= 0.13– tweezers is considered as very weak. This is exemplified by

Table 1. Redox potentials [V] of 3, Zn-3, 5, 6 and Zn-6 vs. Fc/Fc⁺in [nBu₄N][PF₆]/CH₂Cl₂at room temperature.

Ar

E_1/2(P, ox³)

E_1/2(P, ox²)

E_1/2(P, ox¹)

E_1/2(Fc, ox)

E_1/2(P, red¹)

E_1/2(P, red²)

3a

Mes

C₆F₅

Mes

C₆F₅

–

1.040

n.o.

0.730

0.920

0.890

0.880

0.940

1.050

0.880

0.740 (2e)

0.730 (2e)

0.590

0.890

0.440

0.680

0.580

0.590

0.660

0.820

0.600 (2e)

0.610 (2e)

0.420 (2e)

0.400 (2e)

–0.090

–0.100

0.140

0.130

0.140

0.130

0.160

0.150

0.160

0.150

–1.690

–1.430

–1.830

–1.570

–1.610

–1.620

–1.570

–1.400

–2.060

–1.820

–2.230

–1.980

–1.960

–1.900

–1.820

–2.000

–1.960

n.o.^[b]

3e

Zn-3a

Zn-3e

5b

C₆H₅

5c

4-C₆H₄F

4-C₆H₄CF₃

C₆F₅

C₆H₅

4-C₆H₄F

C₆H₅

5d

5e

6b

1.070^[a]

–1.640 (2e)

–1.630 (2e)

–1.830

6c

1.080^[a]

Zn-6b

Zn-6c

–

4-C₆H₄F

–1.910

n.o.^[b]

[a] Only clearly observed in the square-wave voltammogram. [b] Not observed.

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the cyclic voltammograms of 5c and 6c and of their corre-

sponding ferrocene-free reference porphyrins 1a and Ac-4c

in Figure 3. Bis(porphyrins) 6 and Zn-6 can store and re-

lease up to eight and six electrons ([6]^3–···[6]⁵⁺; [Zn-6]^–···[Zn-

6]⁵⁺), respectively; hence, these polyamides can be consid-

ered as multielectron stores.

Figure 4. Normalised absorption and emission spectra of (a) 1a

and 3a; (b) Zn-1a and Zn-3a; (c) 1a, Ac-4b, 5b and 6b and (d) Zn-

1a, Zn-Ac-4b and Zn-6b in CH₂Cl₂at room temperature.

Figure 3. Cyclic voltammograms of 5c and 6c and reference por-

phyrins 1a and Ac-4c in [nBu₄N][PF₆]/CH₂Cl₂.

The electronic absorption spectra of 3, Zn-3, 5, 6 and

The emission spectroscopic data of the dyads and tweez-

Zn-6 are essentially superpositions of the electronic transi- ers are summarised in Table 3. The typical porphyrin fluo-

tions of the porphyrin constituents (Table 2). The absorp- rescence is strongly quenched in the ferrocene porphyrins 3,

tion spectra of selected compounds and their references are Zn-3, 5, 6 and Zn-6 relative to those of the respective refer-

shown in Figure 4. Fully analogous observations were made ence compounds (Figure 4). Thus, the presence of ferrocene

previously concerning the absorption data of amide-linked opens up new nonradiative pathways for the first excited

porphyrins^[10]and anthraquinone–porphyrin–ferrocene tri- singlet state (S₁) decay of the porphyrins. In particular, elec-

ads.^[1f]The characteristic absorption bands of the ferrocene tron transfer from ferrocene to porphyrin should account

moieties are not detectable in the absorption spectra of the for this observation, but energy transfer to ferrocene is also

dyads and tweezers because of the much lower absorptivi- feasible.^[4e,12]Notably, the most efficient fluorescence

ties of (acetylamino)ferrocene (λ_max= 441 nm, ε = 215 quenching in the series 3, Zn-3 and 5 was observed in dyads

m

^–1cm^–1)^[5a]and 1-(acetylamino)ferrocene-1Ј-carboxylic 3e, Zn-3e and 5e with the strongly electron-withdrawing

acid (λ_max= 441 nm, ε = 350 m^–1cm^–1)^[5a]compared with C₆F₅substituent, and the weakest decrease of fluorescence

those of the porphyrins (ε = 4–10ϫ 10⁵m^–1cm^–1). A com- intensity was detected in the dyads with less electron-with-

parison of the absorption spectra of the dyads and tweezers drawing substituents Mes, 4-C₆H₄F and C₆H₅(Table 3).

with those of the corresponding reference porphyrins indi- Similarly, the lower Fc/Fc⁺potential of 3e (E_1/2= –0.09 V)

cates neither new bands nor appreciable shifts of porphyrin compared with that of 5e (E_1/2= +0.13 V) results in a

bands and, thus, a very weak electronic interaction between stronger fluorescence quenching in 3e (Φ = 0.0014) than in

the chromophores in the ground state.^[1f,10]

5e (Φ = 0.0094). These electronic influences already clearly

Table 2. Absorption data of 3, 5, 6 and Zn-6 in CH₂Cl₂at room temperature.

Soret λ_max[nm] Q_y(1,0) λ_max[nm]

Q_y(0,0) λ_max[nm]

Q_x(1,0) λ_max[nm]

(ε/10⁴m^–1cm^–1)

Q_x(0,0) λ_max[nm]

(ε/10⁴m^–1cm^–1)

Ar

(ε/m^–1cm^–1)

(ε/10⁴m^–1cm^–1)

3a

Mes

C₆F₅

Mes

C₆F₅

420 (44.69)

416 (33.50)

424 (30.18)

421 (50.07)

420 (38.93)

420 (39.89)

420 (29.14)

417 (66.61)

419 (78.60)

420 (53.00)

422 (109.44)

420 (82.95)

516 (1.77)

511 (1.69)

552 (1.03)

552 (2.65)

516 (1.68)

516 (1.56)

516 (1.46)

512 (4.26)

516 (3.99)

516 (2.83)

551 (5.48)

549 (5.68)

550 (0.79)

544 (0.30)

594 (0.38)

583 (1.03)

552 (0.88)

552 (0.97)

551 (0.77)

546 (1.37)

551 (2.09)

552 (1.44)

593 (1.62)

588 (2.81)

591 (0.61)

587 (0.42)

–

647 (0.57)

642 (0.54)

–

3e

Zn-3a

Zn-3e

5b

–

C₆H₅

591 (0.53)

591 (0.56)

592 (0.51)

588 (1.45)

592 (1.30)

591 (0.94)

–

647 (0.43)

647 (0.46)

649 (0.43)

643 (0.73)

650 (1.46)

647 (0.97)

–

5c

4-C₆H₄F

4-C₆H₄CF₃

C₆F₅

C₆H₅

4-C₆H₄F

C₆H₅

5d

5e

6b

6c

Zn-6b

Zn-6c

4-C₆H₄F

–

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Table 3. Emission data of 3, Zn-3, 5, 6 and Zn-6 in CH₂Cl₂at room temperature.

τ [ns] (A₁/%); τ [ns] (A₂/%)^[a]Quenching

k_ET

Φ_ET

[e,f]

Ar

Q(0,0)

[nm]

Q(0,1)

[nm]

Φ

[%]^[b]

[10⁹s^–1]^[c,d]

3a

3e

Mes

C₆F₅

653

646

605

598

652

655

649

654

717

714

651

649

717

716

717

0.0122

0.0014

0.0096

0.0006

0.0416

0.0449

0.0255

0.0094

0.0475

0.201 (80); 3.52 (20)

0.022 (91); 2.00 (9)

0.139 (82); 1.56 (18)

0.013 (84); 1.11 (16)

2.00 (75); 5.97 (25)

2.05 (76); 5.48 (24)

1.87 (100)

84

97

90

99

64

55

76

87

4.87

45.36

6.80

76.41

0.40

0.39

0.43

2.91

0.43

0.42

0.23

0.22

1.08

1.19

0.87

0.95

98

100

95

99

80

97

82

80

71

68

75

64

70

Zn-3a Mes

Zn-3e C₆F₅

5b

5c

5d

5e

6b

C₆H₅

4-C₆H₄F

4-C₆H₄CF₃

C₆F₅

0.332 (72); 1.49 (28)

3.17 (100)

C₆H₅

59^[g]

37^[h]

55^[i]

42^[h]

81^[j]

81^[k]

64^[l]

80^[k]

6c

4-C₆H₄F

655

603

597

718

655

653

0.0451

0.0198

0.0203

3.07 (100)

Zn-6b C₆H₅

0.63 (84); 1.87 (16)

0.74 (73); 3.23 (27)

Zn-6c 4-C₆H₄F

[a] The relative amplitudes A were calculated from fitting the data with the equations Y = A₁e^–k/τ1+ A₂e^–k/τ2and A₁+ A₂= 100%. [b]

Φ_ref= 0.0774 (1a), 0.1001 (Zn-1a), 0.0520 (1e), 0.0788 (Zn-1e), 0.1003 (Ac-4c), 0.0569 (Zn-Ac-4c), 0.1167 (Ac-4b), 0.1037 (Zn-Ac-4b),

0.1080 (Ac-4d), 0.0696 (Ac-4e).^[10][c] k_ET= 1/τ – 1/τ_ref. [d] τ_ref= 9.87 (1a), 2.53 (Zn-1a), 10.05 (1b), 1.95 (Zn-1b), 9.88 (4b), 1.99 (Ac-Zn-

4b), 9.98 (Ac-4c), 2.07 (Ac-Zn-4c), 9.64 (Ac-4d), 9.83 (Ac-4e) ns.^[10][e] Φ_ET= k_ETτ. [f] To calculate Φ_ET, τ₁with the largest amplitude

was used. [g] Relative to Ac-4b. [h] Relative to 1a. [i] Relative to Ac-4c. [j] Relative to Zn-Ac-4b. [k] Relative to Zn-1a. [l] Relative to Zn-

Ac-4c.

point to a significant contribution of the reductive PET internal conversion (IC) to the ground state, ISC to the

pathway to the excited-state decay.

T₁(P) state promoted by the heavy-atom effect and energy

The linkage of the second porphyrin unit to dyads 5b transfer to give the ferrocene triplet state T₁(Fc).^[4e,12]

and 5c leads to no significant change of the fluorescence

quantum yield in 6b and 6c (Table 3). Both porphyrin com-

ponents in 6b and 6c feature similar extinction coefficients

at the excitation wavelength, which results in essentially

equal excitation probability. The reduction potentials of the

different porphyrins in the tweezers 6b and 6c (references

1a/Ac-4b and 1a/Ac-4c) are rather similar and, hence, a sim-

ilar PET rate to both excited porphyrins might be expected.

The complexation of tweezers 6 to zinc(II) leads to a further

reduction of the porphyrin fluorescence quantum yield in

Zn-6 by enhancing the intersystem crossing (ISC) rate to

the porphyrin triplet state T₁(P).

To substantiate that the emission quenching essentially

results from PET rather than from energy transfer to ferro-

cene, the low-temperature fluorescence spectra of 1e, 3e, Zn-

1e and Zn-3e were recorded (Figure 5). As 2-methyltetra-

hydrofuran solutions of references 1e and Zn-1e were

cooled to 77 K, there were small increases of the integrated

fluorescence intensities by factors of 1.83 and 1.29, respec-

Figure 5. Normalised emission spectra of 1e, 3e, Zn-1e and Zn-3e

tively. On the other hand, the ferrocene dyads 3e and Zn-

in 2-methyltetrahydrofuran at T = 300Ǟ77 K (λ_exc= 420 nm).

3e enjoy fluorescence increases by factors of 2.88 and 3.38,

respectively. Upon cooling, the corresponding absorption

bands of 1e and 3e sharpen, and the Soret bands increase

The results of fluorescence lifetime measurements in

by a factor of 1.7 in both cases (see Supporting Infor- CH₂Cl₂are summarised in Table 3, and representative de-

mation). Hence, one part of the fluorescence increase is due cay profiles of the dyads and tweezers are displayed in Fig-

to the increase of absorptivity (1e and 3e), whereas an ad- ure 6. Dyad 5d features a monoexponential decay, whereas

ditional process is present for the ferrocenyl porphyrin 3e. all decays of dyads 3 and 5 were best fitted by biexponential

These results support an activated process, such as electron rate laws (Figure 4). We assign the major component (τ₁,

transfer requiring inner- and outer-sphere reorganisation A₁) to the PET pathway, and the minor component (τ₂, A₂)

energy,^[13]as the major decay path for the porphyrin S₁is probably caused by ISC to T₁(P) or energy transfer to

states in ferrocenyl porphyrins in addition to fluorescence, generate T₁(Fc) (vide supra).^[4e,12]All lifetimes τ₁are signifi-

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6c) is again assigned to reductive PET to the N- and C-

terminal porphyrins, and the minor one (τ₂) is due to ISC

to produce the porphyrin triplet state T₁(P) or energy trans-

fer to produce the ferrocene triplet state T₁(Fc).

From the lifetimes, the rate constants for the electron

transfer (k_ET) and quantum efficiencies (Φ_ET) were esti-

mated (Table 3). To correlate the rates with thermodynamic

driving forces, the energies of the P^·––Fc^·+and N-Fmoc–

Fc^·+–P^·–charge-separated (CS) states were estimated

from the oxidation potential of the ferrocene E_1/2(Fc,ox)

and the first reduction potential of the porphyrin moiety

2

E_1/2(P,red¹) including the Coulomb term e₀/[4πε₀ε-

(CH₂Cl₂)r_AD]. The energies of the porphyrin S₁excited

states E(S₀ǞS₁) were estimated as the average value of the

Q_x(0,0) absorption bands and Q(0,0) emission bands

(Tables 2 and 3). The thermodynamic driving forces ΔG_ET

were then estimated according to the Rehm–Weller

equation,^[14]ΔG_ET

=

E_1/2(Fc,ox)

–

E_1/2(P,red¹)

–

2

e₀/[4πε₀ε(CH₂Cl₂)r_AD] – E(S₀ǞS₁) with ε₀= 8.85519ϫ

10^–12Fm^–1, ε(CH₂Cl₂) = 8.93 and r_AD= 13.0 Å for 3a, 3e,

Zn-3a, Zn-3e and 5e and 12.9 Å for 5b–5d (Table 4). The

Coulomb terms in CH₂Cl₂are 0.124 eV for 3a, 3e, Zn-3a,

Zn-3e and 5e and 0.125 eV for 5b–5d. The centre-to-centre

distances (r_AD) were obtained from geometry-optimised

DFT models (vide supra). With ΔG_ET≈ 0.27–0.72 eV, the

PET in the dyads occurs in the normal Marcus region.^[15]

As expected from Marcus theory, the electron-transfer rate

increases with increasing driving force in dyads 3 and 5

(Tables 3 and 4, Figures 7 and 8).

Figure 6. Fluorescence decay profiles of (a) 1a and 3a; (b) Zn-1a

and Zn-3a; (c) 1a, Ac-4b, 5b, 6b and (d) Zn-1a, Zn-Ac-4b and Zn-

6b in CH₂Cl₂(λ_exc= 400 and 550 nm).

cantly reduced compared with those of the reference com-

pounds. Similar to the quantum yields Φ, the lifetimes τ₁

clearly depend on the electron-withdrawing power of the

porphyrin substituents Ar (Table 3, e.g., 3a/3e, Zn-3a/Zn-3e

and 5b/5e) and the Fc/Fc⁺potential in 3e (τ₁= 0.022 ns)

and 5e (τ₁= 0.332 ns).^[1f]

Depending on the initial excitation at either the N-ter-

minal mesityl or C-terminal aryl-substituted porphyrin (Ar

The ferrocene–porphyrin centre-to-centre distances in

= 4-C₆H₅, 4-C₆H₄F: 6b, 6c), the reductive PET in 6 and tweezers 6 and Zn-6 are ca. 13.0 Å, and the Coulomb term

Zn-6 can occur from the central ferrocene to the N or C in CH₂Cl₂is estimated as 0.124 eV. As the first reduction

terminus. In free-base tweezers 6, the decays are monoex- potentials of the different porphyrins in Zn-6 are not indi-

ponential with lifetimes τ ≈ 3 ns. This suggests that both vidually resolved in the cyclic voltammograms, the energies

PET paths

P P

^MesǟFc/FcǞP^C6H5(6b) and ^MesǟFc/ of the CS states of Zn-6 were estimated from the first re-

FcǞP^C6H4F(6c) are conceivable with nearly the same rates duction potentials of suitable reference porphyrins Zn-

or rapid singlet–singlet energy transfer between the por- 1a,^[10]Zn-Ac-4b^[1f]and Zn-Ac-4c.^[10]The estimated energies

phyrins before ET (Table 3). Both are consistent with the for N- and C-terminal CS states of tweezers M(P^Mes·–)–

quantum yields of 5b/6b and 5c/6c (Table 3). The zincated Fc^·+–M(P^Ar) and M(P^Mes)–Fc^·+–M(P^Ar·–) (M = 2H, Zn)

tweezers Zn-6 feature biexponential decays. The dominant and the driving forces ΔG_ETestimated from the Rehm–Wel-

component (τ₁= 0.63 ns for Zn-6b and τ₁= 0.74 ns for Zn- ler equation^[14]are essentially identical, as expected from

Table 4. Energies [eV] of porphyrin S₁and CS states for 3, Zn-3, 5, 6 and Zn-6 and driving forces ΔG_ET

.

Ar

E(S₀ǞS₁)

E(P^·––Fc^·+) or

ΔG_ET(P^·––Fc^·+) o

(P^Mes·––Fc^·+–P^Ar)/(P^Mes–Fc^·+–P^Ar·–

)

r (P_Mes^·––Fc^·+–P^Ar)/(P_Mes–Fc^·+–P₂

)

·–

3a

Mes

C₆F₅

Mes

C₆F₅

1.90

1.92

2.05

2.07

1.90

1.91

1.90

1.89

2.05

2.08

1.48

1.22

1.62

1.35

1.63

1.59

1.41

1.68

–0.42

–0.70

–0.43

–0.72

–0.27

–0.31

–0.50

–0.22

3e

Zn-3a

Zn-3e

5b

C₆H₅

5c

4-C₆H₄F

4-C₆H₄CF₃

C₆F₅

C₆H₅

4-C₆H₄F

C₆H₅

5d

5e

6b

6c

1.66

–0.23

Zn-6b

Zn-6c

1.82^[a]/1.79^[b]

–0.23/–0.26

–0.27/–0.30

4-C₆H₄F

1.81^[a]/1.78^[b]

[a] Calculated with the first reduction potential of Zn-1a E_1/2(P,red¹) = –1.78 V. [b] Calculated with the first reduction potential E_1/2

-

(P,red¹) = –1.75 V of Zn-Ac-4b and Zn-Ac-4c.^[10]

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Figure 9. Energy level diagrams of (a) 6b/6c and (b) Zn-6b/Zn-6c

with the estimated porphyrin triplet state T₁(P) at ca. 1.43 eV,^[16]

the zinc porphyrin triplet state T₁[Zn(P)] at ca. 1.53 eV^[17]and the

ferrocene triplet state T₁(Fc) at ca. 1.16 eV.^[12]The energies of the

triplet states certainly vary with the substituents, as is qualitatively

reflected in the diagram by the thicker energy level bars of the trip-

let states.

Figure 7. Energy level diagrams of (a) 3a/3e and (b) Zn-3a/Zn-3e

with the estimated porphyrin triplet state T₁(P) at ca. 1.43 eV,^[16]

the zinc porphyrin triplet state T₁[Zn(P)] at ca. 1.53 eV^[17]and the

ferrocene triplet state T₁(Fc) at ca. 1.16 eV.^[12]The energies of the

triplet states certainly vary with the substituents, as is qualitatively

reflected in the diagram by the thicker energy level bars of the trip-

let states.

phyrins^[19]and the highest occupied ferrocene-based nearly

degenerate δ orbitals (d_xy, d_x₂_–y₂) for dyads 3a and 3e are

shown in Figure 10. As typically observed, the strongly elec-

tron-withdrawing C₆F₅substituents lead to a local lowest

unoccupied molecular orbital (LUMO) inversion, and the

porphyrin LUMO in 3a features large orbital coefficients at

the linking meso-carbon atoms, whereas nodes are observed

at the linking meso-carbon atoms in 3e.^[1f,19,20]The por-

phyrin highest occupied molecular orbitals (HOMOs) are

located below the ferrocene HOMOs in 3e, whereas one

porphyrin HOMO is found above the ferrocene HOMOs in

3a. The same picture was observed for zincated dyads Zn-

Figure 8. Energy level diagram of 5b–5e with the estimated por-

phyrin triplet state T₁(P) at ca. 1.43 eV^[15]and the ferrocene triplet

state T₁(Fc) at ca. 1.16 eV.^[12]The energies of the triplet states cer- 3a and Zn-3e (see Supporting Information). In the series

tainly vary with the substituents, as is qualitatively reflected in the

diagram by the thicker energy level bars of the triplet states.

5a–5e, the increasing electron-withdrawing power of the

porphyrin substituents lowers the energy of the porphyrin

frontier orbitals (Figure 11), whereas the ferrocene orbitals

the similar optical and redox properties of the constituent remain invariant in energy, as expected from the invariant

porphyrins (Table 4 and Figure 9).

Fc/Fc⁺redox potentials (Table 1). Note that the Fc δ or-

The geometric and electronic structures of the amide- bital energies of 5 are below those of 3/Zn-3 owing to the

linked dyads and tweezers were studied by DFT (B3LYP, electron-withdrawing CO substituent at ferrocene, which is

LANL2DZ, IEFPCM CH₂Cl₂)^[18]approaches. Although consistent with the different Fc/Fc⁺redox potentials of 5

approximate exchange-correlation potentials might not and 3/Zn-3 (Table 1).

yield orbital energies compatible with the experiment, or-

Representatively for all tweezers 6 and Zn-6, the calcu-

bital symmetry and the trends imposed by electronic sub- lated frontier orbitals of 6b, which consist of a twin set of

stituent effects will be correctly reproduced. Hence, no four Gouterman orbitals^[19]and two occupied ferrocene δ

attempts to optimise the amount of Hartree–Fock exchange orbitals (d_xy, d_x₂_–y₂), are depicted in Figure 12. The local

for a better agreement with experimental values were pur- porphyrin HOMOs and LUMOs as well as the ferrocene δ

sued, and the orbital energies given (especially the relative orbitals are essentially pairwise degenerate (Figure 12). The

position of the Fc orbitals with respect to the porphyrin accidental degeneracy of the porphyrin frontier orbitals is

orbitals) shall only be used as a rough guide. The typical caused primarily by cancellation of substituent effects at the

four Gouterman frontier molecular orbitals of por- different porphyrins (Mes/C₆H₄CONHR vs. C₆H₅/

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Figure 11. Calculated (B3LYP/LANL2DZ, IEFPCM) molecular

orbital energy diagram of dyads 5b–5e. The LUMOs of ferrocene

are outside the window shown.

C₆H₄NHCOR or C₆H₄F/C₆H₄NHCOR). In the tweezers,

the porphyrin local LUMOs feature nonzero orbital coeffi-

cients at the meso-carbon bridging atoms. The porphyrin

local HOMOs possess a_2usymmetry with large orbital coef-

ficients at the meso-carbon bridging atoms. This symmetry

allows both reductive PET pathways to generate the N-ter-

minal P^Mes·––Fc^·+–P^Aror C-terminal P^Mes–Fc^·+–P^Ar·–

charge-separated state depending on the initial local exci-

tation of the N-terminal or C-terminal porphyrin.

Furthermore, in addition to the extended tweezers struc-

ture shown in Figure 12, a hydrogen-bonded V-shaped con-

former is conceivable for 6 and Zn-6 (Figure 1, b).^[5a–5d]The

IR spectra suggested the presence of such V-shaped tweez-

ers in solutions of non-coordinating solvents. In the V-

shaped conformers, a slight energy decrease of the P^Mes

frontier orbitals and a slight energy increase of the P^Arfron-

tier orbitals were calculated, as expected for a NH···O hy-

drogen bond from the P^Arporphyrin to the P^Mesporphyrin

(see Supporting Information). The H···O hydrogen bond

distance is 1.87 Å, and the centre-to-centre distance of the

porphyrins is calculated as ca. 15 Å. This distance is too

large to find evidence for a V-shape structure by optical

absorption spectroscopy, and indeed no shift of Soret and

Q bands owing to π–π interactions between the porphyrin

macrocycles was observed. However, a through-space sing-

let–singlet energy transfer in V-shaped 6 and Zn-6 by a

Förster resonance energy transfer mechanism might well

occur over this distance.^[21]The emission energies of the in-

dividual porphyrins in 6 and Zn-6 are too similar to be

distinguished. However, the relative intensities of the Q(0,0)

and Q(0,1) emission bands are slightly different in the re-

spective reference compounds. With this phenomenological

comparison, the emission seems to be favoured from the

mesityl-substituted porphyrin in all cases of 6 and Zn-6 dis-

cussed. This is clearly seen in Figure 4 (d), in which the

band shape of Zn-6b resembles more the band shape of Zn-

1a than that of Zn-Ac-4b. This interpretation is also consis-

tent with findings for analogous ferrocene-free amide-

linked bis(porphyrins) P^Mes–P^Ar.^[10]Further experimental

verification of energy transfer between the porphyrins

within tweezers of type 6 and Zn-6 must await the synthesis

of analogous tweezers featuring more distinct porphyrins

such as mixed free-base and metallated porphyrins; this has

Figure 10. Calculated (B3LYP/LANL2DZ, IEFPCM) frontier or-

bitals of (a) 3a and (b) 3e (isosurface value 0.05 a.u.).

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lower estimated energies for T₁(Fc) than those of the CS

states (Figures 7–9).

To monitor the excited-state and charge-transfer kinetics,

we performed ns–μs transient absorption (TA) pump–probe

experiments on porphyrins 1e and Zn-1e and ferrocenyl

porphyrins 3e and Zn-3e. The ns–μs TA spectra of the par-

ent porphyrins 1e and Zn-1e are characterised by a broad

excited-state absorption that covers almost the entire probe

wavelength range. However, the ground-state bleaching and

stimulated emission of the porphyrin (Figure 13) can be

identified as distinct peak features superimposed on the

broad and featureless excited-state absorption. The corre-

sponding kinetics tracked at different wavelength regions

are shown in Figure 14. The data can be well described by

a sum of two exponentials with lifetimes for 1e of τ₁

=

12.5 ns and τ₂= 105.8 μs. The short component agrees well

with the fluorescence lifetime of ca. 10 ns^[10]as determined

by streak camera experiments within the experimental un-

certainty of the two different measurement techniques. The

longer-lived component τ₂, which has a microsecond life-

time, can be assigned to the recombination of the triplet

state of the porphyrin T₁(P), generated by ISC from the S₁

state. For Zn-1e, we obtained inverse rate constants of τ₁=

2.4 ns and τ₂= 147.5 μs by fitting the experimental data

to a sum of two exponentials. Likewise, we assigned the

nanosecond lifetime τ₁to the fluorescence decay and the

microsecond lifetime τ₂to the recombination of the triplet

state of the porphyrin. In fact, τ₁is essentially similar to

the experimentally measured fluorescence lifetime of 2 ns.

However, we note that here we approach the temporal reso-

lution of our ns–μs TA setup.

Figure 12. Calculated (B3LYP/LANL2DZ, IEFPCM) frontier or-

bitals of 6b (isosurface value 0.05 a.u.).

also been unambiguously demonstrated in amide-linked

bis(porphyrins).^[10]

The proposed V-shaped tweezers structure^[22]prompted

us to attempt to prepare host–guest complexes of 6b and

Zn-6b with 7,7,8,8-tetracyanoquinodimethane (E_1/2

=

–0.30 V in CH₃CN)^[23]and N-ethylanthraquinone-2-carb-

oxamide (E_1/2= –1.28 V in CH₂Cl₂)^[1f]as electron ac-

ceptors. These acceptors could be bound by hydrogen

bonds in the ground state and could give rise to proton-

coupled electron transfer in the excited state of the por-

phyrin.^[24]Titration of the tweezers with more than

Figure 13. Selected ns–μs TA spectra of (a) 1e and (b) Zn-1e in

THF after excitation at 532 nm. The delay times are 500 ps (black),

1000 equiv. of the putative electron acceptors in CH₂Cl₂did 10 ns (red) and 100 μs (green).

not appreciably change the absorption and emission spec-

tra. Hence, significant electron transfer of the excited por-

Interestingly, a photoinduced absorption (PA) feature

phyrins or the porphyrin radical anions (in the CS state) to emerged after 10 ns in the 800 to 850 nm wavelength range

the external acceptor is not observed. This might either be for Zn-1e. We assigned this photoinduced absorption to the

because of unfavourable steric interactions between the po- triplet state of Zn-1e T₁[Zn(P)], as similar PA features have

tential host and guest or a too rapid excited-state decay been reported for triplet states of metallated porphyrins.^[25]

through ferrocene-mediated channels (triplet formation).

The kinetics of this particular wavelength region are shown

Indeed, attempts to calculate P^·––Fc^·+, Zn(P^·–)–Fc^·+and in Figure 14 (b, green curve). Clearly, the signal grows in at

N-Fmoc–Fc^·+–P^·–CS states by DFT methods lead to ferro- early times and reaches its maximum after ca. 10 ns. The

cene triplet states as the lowest triplet state with the spin accumulation of the triplet state of the porphyrin in the first

density localised on the ferrocene moieties (see Supporting 10 ns is in line with the decay of its S₁state, which occurs

Information). This is consistent with the similar or even on the same timescale.

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porphyrin T₁state returns faster to the ground state be-

cause of the heavy-atom effect induced by the presence of

the iron atom in the ferrocene moiety. The integrated TA

kinetics of Zn-3e monitored in the wavelength regions 700–

800 nm (blue curve) and 825 to 850 nm (green curve) are

shown in Figure 16 (b); the main absorption originates from

the zinc porphyrin T₁[Zn(P)] state. For Zn-3e, the data can

be described by a sum of two exponentials. The obtained

lifetimes are τ₁= 1.9 ns and τ₂= 2.3 μs. We assume that we

cannot observe the kinetics of the CS state of Zn-3e because

the photoinduced absorption signal of the porphyrin radi-

cal anion is superimposed by the signal of the zinc por-

phyrin T₁[Zn(P)] state, which indicates that the latter has a

larger cross section than the porphyrin radical anion. The

nanosecond component τ₁describes the kinetics of singlet

excitons, which transfer into the CS state that is not ob-

served in the TA spectra of Zn-3e. We assign τ₂to the decay

of the zinc porphyrin T₁[Zn(P)] state into either the ground

state or the ferrocene T₁(Fc) state, which successively decays

to the ground state. However, the latter is a process that we

cannot directly observe in our TA experiments. In contrast

to the inverse rate constant of τ₃= 88.1 μs observed for 3e,

the inverse rate constant τ₂= 2.3 μs for Zn-3e is signifi-

cantly smaller. Hence, it appears that either of the two pro-

cesses (or both), namely, triplet state decay into the ground

state and energy transfer from the porphyrin T₁[Zn(P)] state

to the ferrocene T₁(Fc) state, is facilitated by the zinc atom

in Zn-3e.

Figure 14. Integrated TA kinetics (750–950 nm) of (a) 1e and (b)

Zn-1e (blue: 700–800 nm; green: 825–850 nm). The red curves are

exponential or biexponential fits to the experimental data.

The ns–μs TA spectra of ferrocenyl-substituted por-

phyrins 3e and Zn-3e are depicted in Figure 15. As the ex-

tinction coefficient of the ferrocenium cation is very small,

the TA spectra are dominated by the excited-state absorp-

tion of the porphyrin, which extends over the entire spectral

range from approximately 500 to 1000 nm. According to

reports by Kubo et al.^[4d]and Pandey et al.,^[26]a photoin-

duced absorption band in the 700 to 900 nm wavelength

range can be assigned to the porphyrin radical anion. They

found radical anion absorption bands in a series of fluorin-

ated porphyrins with maxima between 799–813 nm by

chemical reduction and steady-state absorption. The inte-

grated TA kinetics of the compounds in the wavelength re-

gion above 700 nm are shown in Figure 16. A fit of the

kinetics for 3e to a sum of three exponentials yields inverse

rate constants of τ₁= 6 ns, τ₂= 1.1 μs and τ₃= 88.1 μs. The

inverse rate constant τ₁can be attributed to the decay of

singlet excitons, which are quenched faster than for 1e ow-

ing to the additional PET decay channel. We attribute τ₂to

the lifetime of the CS state, which appears to undergo ISC

to the first triplet excited state T₁(P) of the porphyrin, as

the shape of the spectra after 3 μs resembles the spectral

shape of the T₁(P) state that we also observed for porphyrin

1e. Interestingly, the T₁(P) state of 3e is not as long-lived as

the T₁state of reference porphyrin 1e. It is conceivable that

the triplet state of the porphyrin transfers to the triplet ex-

cited state of the ferrocene T₁(Fc) or alternatively that the

Figure 16. Integrated TA kinetics of (a) 3e (750–950 nm) and (b)

Zn-3e (blue: 700–800 nm; green: 825–850 nm). The red curves are

fits to the experimental data.

Conclusions

The amide-linked porphyrin–ferrocene dyads P^Ar–Fc (3),

Zn(P^Ar)–Fc (Zn-3; Ar = Mes, C₆F₅) and N-Fmoc–Fc–P^Ar

(5; Ar = C₆H₅, 4-C₆H₄F, 4-C₆H₄CF₃, C₆F₅) were prepared

from the corresponding ferrocene and porphyrin building

blocks by amide formation. Two N-Fmoc–Fc–P^Ardyads

(Ar = C₆H₅, 4-C₆H₄F) were further extended to porphyrin–

ferrocene–porphyrin tweezers 6, which were subsequently

metallated with zinc(II) to give Zn-6.

All dyads and tweezers show only weak interactions be-

tween the porphyrin and ferrocene moieties in their ground

states, but there is strong fluorescence quenching and ex-

Figure 15. Selected ns–μs TA spectra of (a) 3e after 0.5 ns, 3 μs and

65 μs and (b) Zn-3e after 0.5 ns, 10 ns and 1 μs in THF solution

after excitation at 532 nm.

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Ti:sapphire ultrafast laser system (Coherent Mira 900 Dual fs–ps

Oscillator) with a repetition rate of 80 MHz and a pulse length of

100 fs pumped by a diode-pumped solid-state laser (Coherent Verdi

V8) was used. The 800 nm output was frequency doubled by using

a barium borate (BBO) crystal to achieve the excitation wavelength

of 400 nm. For the slow sweep measurements, we used a Fianium

fibre laser supercontinuum source (SC450–2), which provides a

white laser light (460–2200 nm) with a pulse width of 6 ps and a

fundamental repetition rate of 20 MHz, which was typically de-

rated by an implemented pulse picker to 1 MHz. The desired exci-

cited-state lifetime reduction with respect to the corre-

sponding ferrocene-free reference compounds. Porphyrin

and ferrocene substituent effects as well as low-temperature

experiments substantiate a reductive photoinduced electron

transfer as the major deactivation pathway of the porphyrin

S₁excited state. The final lowest electronically excited states

are porphyrin and ferrocene triplet states as shown by DFT

calculations and transient absorption measurements. Ad-

ditionally, hints for a singlet–singlet energy-transfer path-

way between the different porphyrins in 6 and Zn-6 were tation wavelength (550 nm) was filtered out of the white light by

using an acousto-optical modulator (AOM, Fianium AOTF).^[29]

found and suggested to occur through a hydrogen-bonded

Transient absorption measurements were performed with a home-

V-shaped structure of the tweezers.

built pump–probe setup.^[29]To measure a time range up to 3 ns

with a resolution of ca. 100 fs, the output of a commercial titani-

um:sapphire amplifier (Coherent LIBRA HE, 3.5 mJ, 1 kHz,

Experimental Section

100 fs) was split; one portion was used to generate a 515 nm exci-

tation pulse by using an optical parametric amplifier (Coherent

Instrumentation: NMR spectra were recorded with a Bruker Avance

OPerA Solo), and the other was used to generate a 1300 nm seed

DRX 400 spectrometer at 400.31 (¹H), 100.05 (¹³C{¹H}) and

pulse [output of an optical parametric amplifier (Coherent OPerA

367.67 MHz (¹⁹F). Chemical shifts (δ) are reported in ppm relative

Solo)] for white-light generation in the visible to NIR (500–

1000 nm) in a c-cut 3 mm thick sapphire window. The variable de-

lay of up to 3 ns between pump and probe was introduced by a

broadband retroreflector mounted on a mechanical delay stage.

to the solvent signal as an internal standard {[D₈]THF (¹H: δ =

1.73, 3.58 ppm; ¹³C: δ = 25.5, 67.7 ppm), CDCl₃(¹H: δ = 7.24 ppm;

¹³C: δ = 77.0 ppm), CD₂Cl₂(¹H: δ = 5.32 ppm; ¹³C: δ = 54.0 ppm)}

or external CFCl₃(¹⁹F: δ = 0 ppm); s = singlet, d = doublet, pt =

The excitation pulse was chopped at 500 Hz, and the white light

pseudotriplet (unresolved doublet of doublets), dd = doublet of

pulses were dispersed onto linear silicon (Hamamatsu NMOS lin-

doublets, ddd = doublet of doublet of doublets, br s = broad sing-

ear image sensor S3901 photodiode). The array was read out at

let. IR spectra were recorded with a BioRad Excalibur FTS 3100

1 kHz. Adjacent diode readings corresponding to the transmission

spectrometer with samples as CsI disks. Signal intensities: vs = very

of the sample after an excitation pulse and without an excitation

strong, s = strong, m = medium, w = weak. ESI and high-resolu-

tion (HR) ESI mass spectra were recorded with a Micromass Q-

TOF-Ultima spectrometer. Field desorption (FD) mass spectra

pulse were used to calculate ΔT/T. Samples were excited with flu-

ences of ca. 100 μJcm^–2.

Density functional calculations were performed with the

Gaussian09 series^[18]of programs. The B3LYP formulation of den-

sity functional theory was used, and the LANL2DZ basis set was

employed. To include solvent effects, the integral equation formal-

ism polarisable continuum model (IEFPCM, CH₂Cl₂) was em-

ployed. No symmetry constraints were imposed on the molecules.

The presence of energy minima of the ground states was checked

by analytical frequency calculations.

were obtained with a FD Finnigan MAT95 spectrometer. Cyclic

voltammetry (CV) and square-wave voltammetry measurements

were performed with a BioLogic SP-50 voltammetric analyser with

samples in CH₂Cl₂containing 0.1 m [nBu₄N][PF₆] as supporting

electrolyte at a glassy carbon working electrode with a platinum

wire counter electrode and a 0.01 m Ag/AgNO₃reference electrode.

All cyclic voltammetric measurements were recorded at 100 mVs^–1

scan speed. Ferrocene was employed as an internal reference redox

system.

Materials: Unless otherwise noted, all chemical reagents were used

without any further purification as received from suppliers (Sigma–

Aldrich, Acros, Alfa Aesar). THF was freshly distilled from so-

dium. CH₂Cl₂and 1,2-dichloroethane were freshly distilled from

calcium hydride. Porphyrins 1a, 2a, Zn-1a, 1e, 2e, 4b–4e, Ac-4b–

Ac-4e, Zn-Ac-4b, Zn-Ac-4c, aminoferrocene and N-Fmoc-pro-

tected ferrocene amino acid were prepared by published pro-

cedures.^{[2d,5a,8–10,30–33]}

UV/Vis/NIR absorption spectra were measured with a Varian Cary

5000 spectrometer with samples in CH₂Cl₂in 1.0 cm cells (Hellma,

suprasil). Steady-state emission spectra were recorded with a Var-

ian Cary Eclipse spectrometer with samples in CH₂Cl₂in 1.0 cm

cells (Hellma, suprasil). Quantum yields Φ were determined by

comparing the areas under the emission spectra on an energy scale

[cm^–1] recorded for optically matched solutions (absorption inten-

sity under 0.05) of the samples and the reference [Φ(H₂TPP) = 0.13

General Procedure for the Preparation of 3a and 3e: 5-(4-Carb-

oxyphenyl)-15-(4-methoxycarbonylphenyl)-10,20-bis(2,4,6-trimeth-

ylphenyl)porphyrin (2a) or 5-(4-carboxyphenyl)-15-(4-methoxy-

carbonylphenyl)-10,20-bis(2,3,4,5,6-pentafluorophenyl)porphyrin

(2e; 1 equiv.) and pyridine (1 mL) were dissolved in anhydrous tolu-

ene (20 mL). Thionyl chloride (5 equiv.) was added, and the reac-

tion mixture was stirred under nitrogen for 3 h at room tempera-

ture. The excess thionyl chloride and solvent were removed under

reduced pressure. The residue was redissolved in toluene (20 mL)

and pyridine (1 mL) in an ultrasonic bath. Aminoferrocene

(1.3 equiv.) dissolved in toluene (20 mL) and pyridine (1 mL) were

added. The mixture was stirred overnight, and the solvent was re-

moved by evaporation under reduced pressure. The residue was

purified by chromatography [silica, toluene/ethyl acetate (20:1)].

in benzene]^[27]and using the equation^[28]Φ = Φ_refϫI/I_refϫη²/η²

ref

with η(benzene) = 1.5011, η(CH₂Cl₂) = 1.4242 and η(THF) =

1.4070; experimental uncertainty 15%. Fluorescence decay mea-

surements were performed with ca. 1ϫ10^–5m solutions by the

time-correlated single photon counting method with a Hamamatsu

streak camera system. Two time modes were used for the measure-

ments: one with a resolution down to a few picoseconds and a

maximum time range of two nanoseconds [fast sweep, mononuclear

zinc(II) porphyrins, P–Fc, Zn(P)–Fc dyads and N-Fmoc–Fc–P^Ar

with Ar = C₆F₅], and a second time mode with a time resolution

down to a few hundred picoseconds and a maximum time range

limited by the repetition rate of the excitation source [slow sweep,

all free-base porphyrins, N-Fmoc–Fc–P^Ardyads, P^Mes–Fc–P^Arand

Zn(P^Mes)–Fc–Zn(P^Ar

)

tweezers]. Excitation was provided de-

General Procedure for the Preparation of Zn-3a and Zn-3e: Dyad

3a or 3e (1 equiv.) and zinc(II) acetate dihydrate (5 equiv.) were

pending on the measuring mode. For fast-sweep experiments, a

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FULL PAPER

stirred overnight in CH₂Cl₂(5 mL). After concentration under re-

duced pressure, the product was isolated by column chromatog-

raphy.

Acknowledgments

This work was supported by the Deutsche Forschungsgemeinschaft

(DFG) (He 2778-6/1). J. R. O. thanks the International Research

Training Group (IRTG 1404) “Self Organized Materials for Opto-

electronics” for funding, M. M. thanks the Max Planck Graduate

Center with the Johannes Gutenberg University (MPGC) for sup-

port and F. L. thanks the Max Planck Society for funding a Max

Planck Research group.

General Procedure for the Preparation of 5b, 5c, 5d and 5e: N-Fmoc-

protected ferrocene amino acid N-Fmoc-Fca-OH (H-Fca-OH = 1-

amino-1Ј-ferrocene carboxylic acid; Fmoc = 9-fluorenylmethoxy-

carbonyl) and one drop of pyridine were dissolved in anhydrous

CH₂Cl₂(40 mL). Oxalyl chloride was added, and the reaction mix-

ture was stirred under nitrogen for 1 h at room temperature. The

excess oxalyl chloride and solvent were removed by evaporation

under reduced pressure. The residue was dissolved in CH₂Cl₂

(10 mL), and the solvent was removed under reduced pressure. The

acid chloride was dissolved in CH₂Cl₂(40 mL). To this solution, a

solution of the porphyrin amino component in CH₂Cl₂(40 mL

with one drop of pyridine) was added. The reaction mixture was

stirred for 18 h at room temperature and washed with water, and

the organic phase was concentrated under reduced pressure. The

product was isolated by column chromatography.

[1] a) H. Imahori, D. M. Guldi, K. Tamaki, Y. Yoshida, C. Luo,

Y. Sakata, S. Fukuzumi, J. Am. Chem. Soc. 2001, 123, 6617–

6628; b) H. Imahori, K. Tamaki, Y. Araki, Y. Sekiguchi, O.

Ito, Y. Sakata, S. Fukuzumi, J. Am. Chem. Soc. 2002, 124,

5165–5174; c) H. Imahori, Y. Sekiguchi, Y. Kashiwagi, T. Sato,

Y. Araki, O. Ito, H. Yamada, S. Fukuzumi, Chem. Eur. J. 2004,

10, 3184–3196; d) M. U. Winters, E. Dahlstedt, H. E. Blades,

C. J. Wilson, M. J. Frampton, H. L. Anderson, B. Albinsson,

J. Am. Chem. Soc. 2007, 129, 4291–4297; e) C. Wijesinghe,

M. E. El-Khouly, M. E. Zandler, S. Fukuzumi, F. D’Souza,

Chem. Eur. J. 2013, 19, 9629–9638; f) J. Melomedov, J. R. Ochs-

mann, M. Meister, F. Laquai, K. Heinze, Eur. J. Inorg. Chem.

2014, 1984–2001.

[2] a) D. Gust, T. A. Moore, A. L. Moore, F. Cao, D. Luttrull,

J. M. DeGraziano, X. C. Ma, L. R. Makings, S. Lee, T. T. Trier,

E. Bittersmann, G. R. Seely, S. Woodward, R. V. Bensasson,

M. Roug, F. C. De Schryver, M. Van der Auweraer, J. Am.

Chem. Soc. 1991, 113, 3638–3649; b) D. Gust, T. A. Moore,

A. L. Moore, A. N. Macpherson, A. Lopez, J. M. DeGraziano,

I. Gouni, E. Bittersmann, G. R. Seely, F. Gao, R. A. Nieman,

X. C. Ma, L. J. Demanche, S. Hung, D. K. Luttrull, S. Lee,

P. K. Kerrigan, J. Am. Chem. Soc. 1993, 115, 11141–11152; c)

M. D. Meijer, G. P. M. van Klink, G. van Koten, Coord. Chem.

Rev. 2002, 230, 141–163; d) S. L. Gould, G. Kodis, R. E. Pala-

cios, L. De La Garza, A. Brune, D. Gust, T. A. Moore, A. L.

Moore, J. Phys. Chem. B 2004, 108, 10566–10580.

[3] a) A. M. Brun, A. Harriman, V. Heitz, J.-P. Sauvage, J. Am.

Chem. Soc. 1991, 113, 8657–8663; b) V. Heitz, S. Chardon-

Noblat, J.-P. Sauvage, Tetrahedron Lett. 1991, 32, 197–198; c)

E. K. L. Yeow, P. J. Sintic, N. M. Cabral, J. N. H. Reek, M. J.

Crossley, K. P. Ghiggino, Phys. Chem. Chem. Phys. 2000, 2,

4281–4291; d) K. Kilså, J. Kajanus, A. N. Macpherson, J.

Mårtensson, B. Albinsson, J. Am. Chem. Soc. 2001, 123, 3069–

3080; e) S. Fukuzumi, K. Ohkubo, W. E, Z. Ou, J. Shao, K. M.

Kadish, J. A. Hutchison, K. P. Ghiggino, P. J. Sintic, M. J.

Crossley, J. Am. Chem. Soc. 2003, 125, 14984–14985; f) J.

Hee Jang, H. J. Kim, H.-J. Kim, C. H. Kim, T. Joo, D.

Won Cho, M. Yoon, Bull. Korean Chem. Soc. 2007, 28, 1967–

1972; g) J. Fortage, J. Boixel, E. Blart, L. Hammarström, H. C.

Becker, F. Odobel, Chem. Eur. J. 2008, 14, 3467–3480; h) J.

Fortage, A. Scarpaci, L. Viau, Y. Pellegrin, E. Blart, M. Falk-

enström, L. Hammarström, I. Asselberghs, R. Kellens, W. Li-

baers, K. Clays, M. P. Eng, F. Odobel, Chem. Eur. J. 2009, 15,

9058–9067; i) J. Fortage, J. Boixel, E. Blart, H. C. Becker, F.

Odobel, Inorg. Chem. 2009, 48, 518–526.

[4] a) R. Giasson, E. J. Lee, X. Zhao, M. S. Wrighton, J. Phys.

Chem. 1993, 97, 2596–2601; b) N. B. Thornton, H. Wojtowicz,

T. Netzel, D. W. Dixon, J. Phys. Chem. B 1998, 102, 2101–

2110; c) V. A. Nadtochenko, N. N. Denisov, V. Yu. Gak, N. V.

Abramova, N. M. Loim, Russ. Chem. Bull. 1999, 40, 1900–

1903; d) M. Kubo, Y. Mori, M. Otani, M. Murakami, Y. Ishib-

ashi, M. Yasuda, K. Hosomizu, H. Miyasaka, H. Imahori, S.

Nakashima, Chem. Phys. Lett. 2006, 429, 91–96; e) H. Mans-

our, M. E. El-khouly, S. Y. Shaban, O. Ito, N. Jux, J. Porphyrins

Phthalocyanines 2007, 10, 719–728; f) P. K. Poddutoori,

A. S. D. Sandanayaka, T. Hasobe, O. Ito, A. van der Est, J.

Phys. Chem. B 2010, 114, 14348–14357; g) M. A. Bakar, N. N.

Sergeeva, T. Juillard, M. O. Senge, Organometallics 2011, 30,

3225–3228; h) B. M. J. M. Suijkerbuijk, R. J. M. Klein Geb-

General Procedure for the Preparation of 6b and 6c: Compound

5b or 5c and tris(2-aminoethyl)amine were dissolved in anhydrous

CH₂Cl₂(20 mL), and the reaction mixture was stirred under nitro-

gen for 3 h at room temperature and washed with saturated brine

(2ϫ 10 mL) and phosphate buffer (pH 5.5). The solution was dried

with Na₂SO₄, and the solvent was removed under reduced pressure.

5-(4-Carboxyphenyl)-15-(4-methoxycarbonylphenyl)-10,20-

bis(2,4,6-trimethylphenyl) porphyrin (2a) was dissolved in anhy-

drous CH₂Cl₂(30 mL), 1-chloro-N,N,2-trimethylpropenylamine

(Ghosez’s reagent) was added, and the reaction mixture was stirred

under nitrogen for 1 h at room temperature. After the acid chloride

formed (TLC control), the excess Ghosez’s reagent and solvent

were removed by evaporation under reduced pressure. To remove

the N,N-dimethylamide byproduct, anhydrous CH₂Cl₂(20 mL) was

added, and the volatiles were again removed by evaporation. The

acid chloride was dissolved in CH₂Cl₂(30 mL with 0.05 mL of tri-

ethylamine), and this solution was added dropwise to a solution of

the amino component prepared from 5b or 5c in CH₂Cl₂. The reac-

tion mixture was stirred for 18 h at room temperature and washed

with water, and the organic phase was concentrated under reduced

pressure. After column chromatography, 6b and 6c were isolated.

General Procedure for the Preparation of Zn-6b and Zn-6c: Com-

pound 6b or 6c (1 equiv.) and zinc(II) acetate dihydrate (12 equiv.)

were stirred overnight in CH₂Cl₂(10 mL). After concentration un-

der reduced pressure, the product was isolated by column

chromatography [silica, toluene/ethyl acetate 50:1].

[10,20-Bis(pentafluorophenyl)-5,15-bis(4-methoxycarbonylphenyl)por-

phyrinato]zinc(II) (Zn-1e): Porphyrin 1e (50 mg, 0.054 mmol) and

zinc(II) acetate dihydrate (61 mg, 0.27 mmol) were stirred overnight

in CH₂Cl₂(10 mL). After concentration under reduced pressure,

the product was isolated by column chromatography [silica,

CH₂Cl₂, R_f= 0.50], yield 49.9 mg (0.051 mmol, 94%), purple-red

powder. C₄₈H₂₂F₁₀N₄O₄Zn (974.1067).

Supporting Information (see footnote on the first page of this arti-

cle): Complete analytical data; absorption spectra of 1e and 3e in

2-methyltetrahydrofuran at T = 300Ǟ77 K; B3LYP/LANL2DZ,

IEFPCM calculated frontier orbitals of Zn-3a, Zn-3e, 5d, 5e, 6c,

Zn-6b and Zn-6c; B3LYP/LANL2DZ, IEFPCM calculated mo-

lecular orbital energy diagrams of 3a, 3e, Zn-3a, Zn-3e, 6b, 6c, Zn-

6b and Zn-6c; B3LYP/LANL2DZ, IEFPCM calculated spin densi-

ties of the lowest triplet state of 3e and 5e; Cartesian coordinates

of all DFT-optimised geometries.

Eur. J. Inorg. Chem. 2014, 2902–2915

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FULL PAPER

bink, Angew. Chem. Int. Ed. 2008, 47, 7396–7421; Angew.

Chem. 2008, 120, 7506–7532; i) S. J. Dammer, P. V. Solntsev,

J. R. Sabin, V. N. Nemykin, Inorg. Chem. 2013, 52, 9496–9510;

j) L. Lvova, P. Galloni, B. Floris, I. Lundström, R. Paolesse,

C. Di Natale, Sensors 2013, 13, 5841–5856; k) V. N. Nemykin,

P. Chen, P. V. Solntsev, A. A. Purchel, K. M. Kadish, J. Por-

phyrins Phthalocyanines 2012, 16, 793–801; l) A. Vecchi, E.

Gatto, B. Floris, V. Conte, M. Venanzi, V. N. Nemykin, P. Gal-

loni, Chem. Commun. 2012, 48, 5145–5147; m) V. N. Nemykin,

G. T. Rohde, C. D. Barrett, R. G. Hadt, J. R. Sabin, G. Reina,

P. Galloni, B. Floris, Inorg. Chem. 2010, 49, 7497–7509; n) V. N.

Nemykin, G. T. Rohde, C. D. Barrett, R. G. Hadt, C. Bizzarri,

P. Galloni, B. Floris, I. Nowik, R. H. Herber, A. G. Marrani,

R. Zanoni, N. M. Loim, J. Am. Chem. Soc. 2009, 131, 14969–

14978.

a) K. Heinze, M. Schlenker, Eur. J. Inorg. Chem. 2004, 2974–

2988; b) K. Heinze, D. Siebler, Z. Anorg. Allg. Chem. 2007,

633, 2223–2233; c) D. Siebler, M. Linseis, T. Gasi, L. M. Car-

rella, R. F. Winter, C. Förster, K. Heinze, Chem. Eur. J. 2011,

17, 4540–4551; d) D. Siebler, C. Förster, K. Heinze, Dalton

Trans. 2011, 40, 3558–3575; e) H. Huesmann, C. Förster, D.

Siebler, T. Gasi, K. Heinze, Organometallics 2012, 31, 413–427.

A. K. Burrell, W. Campbell, D. L. Officer, Tetrahedron Lett.

1997, 38, 1249–1252.

K. Heinze, K. Hempel, M. Beckmann, Eur. J. Inorg. Chem.

2006, 2040–2050.

C. M. Carcel, J. K. Laha, R. S. Loewe, P. Thamyongkit, K.

Schweikart, V. Misra, D. F. Bocian, J. S. Lindsey, N. Carolina,

J. Org. Chem. 2004, 69, 6739–6750.

K. Heinze, A. Reinhart, Dalton Trans. 2008, 469–480.

J. Melomedov, A. Wünsche von Leupoldt, M. Meister, F. La-

quai, K. Heinze, Dalton Trans. 2013, 42, 9727–9739.

A. Devos, J. Remiona, A.-M. Frisque-Hesbain, A. Colens, L.

H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Son-

nenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hase-

gawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,

T. Vreven, J. A. Montgomery Jr., J. E. Peralta, F. Ogliaro, M.

Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Starov-

erov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell,

J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M.

Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Ad-

amo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev,

A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Mar-

tin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,

J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B.

Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09,

revision A.02, Gaussian Inc., Wallingford CT, 2009.

[19] M. Gouterman, J. Chem. Phys. 1959, 30, 1139–1161.

[20] D. Holten, D. F. Bocian, J. S. Lindsey, Acc. Chem. Res. 2002,

35, 57–69.

[5]

[21] J.-M. Camus, S. M. Aly, C. Stern, R. Guilard, P. D. Harvey,

Chem. Commun. 2011, 47, 8817–8819.

[22] a) S. Brahma, S. A. Ikbal, S. P. Rath, Inorg. Chem. 2014, 53,

49–62; b) H. Yoon, C.-H. Lee, W.-D. Jang, Chem. Eur. J. 2012,

18, 12479–12486; c) A. Chaudhary, S. P. Rath, Chem. Eur. J.

2012, 18, 7404–7417; d) A. Chaudhary, S. P. Rath, Chem. Eur.

J. 2011, 17, 11478–11487; e) B. Habermeyer, A. Takai, C. P.

Gros, M. El Ojaimi, J.-M. Barbe, S. Fukuzumi, Chem. Eur. J.

2011, 17, 10670–10681; f) J.-M. Barbe, B. Habermeyer, T.

Khoury, C. P. Gros, P. Richard, P. Chen, K. M. Kadish, Inorg.

Chem. 2010, 49, 8929–8940.

[23] N. G. Connelly, W. E. Geiger, Chem. Rev. 1996, 96, 877–910.

[24] O. S. Wenger, Chem. Eur. J. 2011, 17, 11692–11702.

[25] J. Rodriguez, C. Kirmaier, D. Holten, J. Am. Chem. Soc. 1989,

111, 6500–6506.

[26] S. K. Pandey, A. L. Gryshuk, A. Graham, K. Ohkubo, S. Fu-

kuzumi, M. P. Dobhal, G. Zheng, Z. Ou, R. Zhan, K. M. Kad-

ish, A. Oseroff, S. Ramaprasade, R. K. Pandey, Tetrahedron

2003, 59, 10059–10073.

[27] A. Rosa, G. Ricciardi, E. J. Baerends, A. Romeo, L. Monsu, J.

Phys. Chem. A 2003, 107, 11468–11482.

[28] J. R. Lakowicz, Principles of Fluorescence Spectroscopy, 3rd ed.,

Springer, New York, 2006.

[29] F. Etzold, I. A. Howard, N. Forler, D. M. Cho, M. Meister, H.

Mangold, J. Shu, M. R. Hansen, K. Müllen, F. Laquai, J. Am.

Chem. Soc. 2012, 134, 10569–10583.

[30] D. T. Gryko, M. Tasior, B. Koszarna, J. Porphyrins Phthalocy-

anines 2003, 7, 239–248.

[31] T. Rohand, E. Dolusic, T. H. Ngo, W. Maes, W. Dehaen, AR-

KIVOC 2007, 10, 307–324.

[6]

[7]

[8]

[9]

[10]

[11]

Ghosez, J. Chem. Soc., Chem. Commun. 1979, 1180–1181.

[12] Y. Araki, Y. Yasumura, O. Ito, J. Phys. Chem. B 2005, 109,

9843–9848.

[13] E. D. German, A. M. Kuznetso, Electrochim. Acta 1981, 26,

1595–1608.

[14] A. Weller, Z. Phys. Chem. (Muenchen Ger.) 1982, 133, 93–98.

[15] a) R. A. Marcus, J. Chem. Phys. 1956, 24, 979–989; b) R. A.

Marcus, Annu. Rev. Phys. Chem. 1964, 15, 155–196; c) R. A.

Marcus, Angew. Chem. Int. Ed. Engl. 1993, 32, 1111–1121; An-

gew. Chem. 1996, 105, 1161–1172.

[16] J. A. Schmidt, A. R. McIntosh, A. C. Weedon, J. R. Bolton,

J. S. Connolly, J. K. Hurley, M. R. Wasielewski, J. Am. Chem.

Soc. 1988, 110, 1733–1740.

[17] C. Luo, D. M. Guldi, H. Imahori, K. Tamaki, Y. Sakata, J.

Am. Chem. Soc. 2000, 122, 6535–6551.

[18] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,

M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B.

Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li,

[32] B. J. Littler, Y. Ciringh, J. S. Lindsey, J. Org. Chem. 1999, 64,

2864–2872.

[33] K. Heinze, A. Reinhart, Z. Naturforsch. B 2005, 60, 758–762.

Received: March 5, 2014

Published Online: May 26, 2014

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2915

Article Doi

Aminoferrocene and ferrocene amino acid as electron donors in modular porphyrin-ferrocene and porphyrin-ferrocene-porphyrin conjugates

DOI: 10.1002/ejic.201402138

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Article abstract of DOI:10.1002/ejic.201402138

Full text of DOI:10.1002/ejic.201402138

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