Iron(III) bromide catalyzed bromination of 2-tert-butylpyrene and corresponding position-dependent aryl-functionalized pyrene derivatives

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ARTICLE

Iron (III) bromide catalyzed bromination of 2-tert-

butylpyrene and corresponding positions-dependent

aryl-functionalized pyrene derivatives

Cite this: DOI: 10.1039/x0xx00000x

Xing Feng,^a,bJianꢀYong Hu,^b,cHirotsugu Tomiyasu,^bZhu Tao,^dCarl Redshaw,^eMark R.J.

Elsegood,^fLynne Horsburgh,^fSimon J. Teat,^gXianꢀFu Wei,^aand Takehiko Yamato^*b

Received 00th January 2012,

Accepted 00th January 2012

DOI: 10.1039/x0xx00000x

The present work probes the bromination mechanism of 2ꢀtertꢀbutylpyrene (1), which

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regioselectively affords monoꢀ, diꢀ, triꢀ, and tetraꢀbromopyrenes, by theoretical calculation and

detailed experimental methods. Bromine atom may directed to the Kꢀregion (positions 5ꢀ and

9ꢀ) instead of the more reactive positions 6ꢀ and 8ꢀposition in the presence of iron powder. In

this process, FeBr₃plays a significant role to release of steric hindrance or lowing the

activation energy of the rearrangement. The intermediate bromopyrene derivatives were

1

isolated and confirmed by H NMR spectra, mass spectroscopy and elemental analysis. Further

evidence on substituent positions originated from a series of aryl substituted pyrene

derivatives, which were obtained from the corresponding bromopyrenes on reaction with 4ꢀ

methoxyꢀ phenylboronic acid by a SuzukiꢀMiyaura crossꢀcoupling reaction. All of Positionsꢀ

dependent arylꢀfunctionalized pyrene derivatives are characterized by single Xꢀray diffraction,

¹H/¹³C NMR, FTꢀIR and MS, and offered a straightforward proof to support our conclusion.

Furthermore, the photophysical properties of series of compounds were confirmed by

fluorescence and absorption, as well as by fluorescence lifetime measurements.

Introduction

hand, the active sites, namely the 1ꢀ, 3ꢀ, 6ꢀ, and 8ꢀpositions have

been thoroughly examined and the products used in a variety of

Pyrene and its derivatives¹belong to a classical family of polycyclic

aromatic hydrocarbons (PHAs) that have been extensively

investigated for lightꢀemitting device applications over recent years.

This interest stems from their inherent chemical and photochemical

characteristics, in particular an excellent deep blue chromophore

which exhibits great chemical stability and high charge carrier

mobility. However, owing to its planar structure, pyrene has a strong

tendency to form πꢀaggregates/excimers, which, inꢀturn, leads to an

excimer emission band and the quenching of fluorescence in

condensed media and a resulting low fluorescence quantum yield.

With this in mind, enormous effort has been paid towards exploring

new methods to functionalize the pyreneꢀcore for developing

molecular materials and applications thereof.

In general, due to the presence of nodal planes located at the 2ꢀ

and 7ꢀpositions in both the highest occupied molecular orbital’s

(HOMO) and the lowest unoccupied molecular orbital’s (LUMO) of

pyrene, substituting pyrene at the 2ꢀ and/or 2,7ꢀpositions is more

difficult compared to other positions (such as 1ꢀ, 3ꢀ, 6ꢀ and 8ꢀ

positions (active site)).²Thus, there are few examples which focus

on substituting at the 2ꢀ and 7ꢀpositions of pyrene by borylation,³

bromination,⁴nitration,⁵oxidation⁶and tertꢀbutylation.⁷On the other

applications as optical materials.^1a,1bSince we first reported⁸the

oxidation of pyrene at the Kꢀregion (4ꢀ, 5ꢀ, 9ꢀ and 10ꢀpositions) in

1997 by stepwise synthetic methods, the Kꢀregion also has been

explored as a convenient synthetic route to the ketone⁹and used for

preparing pyreneꢀfused azaacene derivatives for application

inorganic semiconductors.¹⁰

As previously mentioned, bromopyrenes are significant

intermediate compounds which play an important role in modern

organic chemistry, not only for synthetic methodology, but also for

advanced optoelectronic materials. Commonly, the 1ꢀ, 3ꢀ, 6ꢀ, and 8ꢀ

positions of pyrene preferentially undergo electrophilic aromatic

substitution (S_EAr) reactions. Therefore, monoꢀ, bisꢀ, triꢀ, and

tetrakisꢀsubstituted pyrenes were synthesized for organic electronic

devices¹and fluorescence probes.¹¹For example, Thummel et al.¹²

discussed the crystal packing of 1,3ꢀ, 1,6ꢀ, 1,8ꢀ, and 2,7ꢀbis(2ꢀ

[1,10]phenanthrolinyl)pyrenes and their use as pyreneꢀbridging

ligands in ruthenium(II) chemistry, as evidenced by ¹H NMR spectra

and singleꢀcrystal Xꢀray crystallography. Sankararaman¹³and coꢀ

workers reported a pyrene octaaldehyde derivative from 1,3,6,8ꢀ

tetrabromopyrene, which can cause molecular aggregations in

nonpolar solvents and in the solidꢀstate through cooperativity of the

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intermolecular πꢀπ stacking and C–H···O interactions, which has

It is well known that bromination reactions can be violent and

potential application in the field of molecular optoelectronics. complex processes, thus to investigate the bromination mechanism is

Chow¹⁴and coꢀworkers synthesized sterically congested tetraarylꢀ far from simple, because it is difficult to capture the transition state

pyrenes as efficient blue emitters that exhibited pureꢀblue or a transition state analogue by experimental methods. Given this,

electroluminescence and formed respectable organic lightꢀemitting the mechanism of electrophilic substitution was generally

diodes (OLEDs). More recently, Konishi¹⁵and coꢀworkers investigated by kinetic and stereochemical studies, or by theoretical

systematically alkylated the active sites, namely the 1ꢀ, 3ꢀ, 6ꢀ, and 8ꢀ analyses.²³In additional, if the experimental conditions cannot be

positions of pyrene, and investigated the effects of the number of well controlled, then the final components will be complicated and

alkyl substituents on the photophysical properties of the pyrene hard to characterize.²⁴In this paper, we present the first example of

chromophores. Recently, we reported a new type of fluorescent the systematic exploration of the bromination rearrangement reaction

sensor based on a pyreneꢀlinked triazoleꢀmodified hexahomotrioxaꢀ of pyrene affording the monoꢀ, diꢀ, triꢀ, and tetraꢀbromopyrenes by

calix[3]arene, which used the 1ꢀpyrenyl moiety for selectively detailed experimental procedures and theoretical calculation. And

detecting Zn²⁺and H₂PO₄^–ions in neutral solutions.¹⁶

the corresponding positionsꢀdependent arylpyrenes derivatives

Bromination of the pyrene not only occurred at the active sites of containing the 4ꢀmethoxyphenyl group were synthesized from the

1ꢀ, 3ꢀ, 6ꢀ, and 8ꢀpositions, but also substitution occurred at the Kꢀ corresponding bromopyrenes via a SuzukiꢀMiyaura crossꢀcoupling

region, namely the 4ꢀ, 5ꢀ, 9ꢀ, and 10ꢀpositions. For instance, our reaction, which was characterized by single crystal Xꢀray diffraction

group reported a series of pyreneꢀbased cruciform/handꢀshaped and ¹H NMR spectroscopy. The detailed results have strongly

lightꢀemitting monomers with highly emissive pureꢀblue supported the bromoꢀsubstituted positions in the pyrene ring as

fluorescence from tetrabromo/pentabromopyrene.¹⁷Very recently, previous assumption. Furthermore, the effects of the methoxyphenyl

we explored a new bromide precursor, 1,3,5,9ꢀtetrabromoꢀ7ꢀtertꢀ group (both number and the substitution pattern) on their

butylpyrene,¹⁸prepared via bromination of 2ꢀtertꢀbutylpyrene (1) in photophysical properties, as well as for their molecular packing,

CH₂Cl₂at room temperature using iron powder as the catalyst.

About twenty years ago, we reported FeBr₃ꢀcatalyzed

were investigated.

a

Results and discussion

rearrangement of a pyreneꢀbased material in which the bromine atom

was transferred from the active site (1ꢀposition) to the Kꢀregion (4ꢀ

position), ie bromination of 2,7ꢀdiꢀtertꢀbutylpyrene with 1.1 mole

equiv. of bromine in the presence of iron powder to afford 1ꢀbromoꢀ

2,7ꢀdiꢀtertꢀbutylpyrene, which can be further brominated with excess

bromine in the presence of FeBr₃ꢀcatalyzed, and afforded 4,5,9,10ꢀ

tetrabromoꢀ2,7ꢀdiꢀtertꢀbutylpyrene (Scheme 1).⁸However, the

detailed bromination mechanism still remains unclear.

Stoichiometric bromination of 2-tert-butylpyrene (1)

A threeꢀneck round bottom flask fitted with a dropping funnel and a

CaCl₂drying tube, was filled with 1 (200 mg, 0.78 mmol) in 20 mL

of CH₂Cl₂and was stirred for 30 min. at 0 °C. A solution of Br₂

(depending on stoichiometric ratio) in 5 mL of CH₂Cl₂was added

dropꢀwise. After the addition of bromine was completed, the mixture

was warmed to room temperature (28 °C) and stirred for 5 h. The

crude product was washed with hot hexane and the yields of

products are compiled in Table 1.

2

Br

3

6

3

1

8

1

4

10

9

Br

Fe/Br₂

CCl₄

4

5

FeBr₃

CCl₄

Br

10

9

4

5

10

9

Br

Br Br

Br

5

bromination

6

8

Br

7

Br

Scheme 1. FeBr₃ꢀcatalyzed rearrangement to afford 4,5,9,10ꢀtetrabromoꢀ2,7ꢀ

diꢀtertꢀbutylpyrene.

1

2a

2b

2d

2e

2c

2f

Scheme 2. Bromination of 2ꢀtertꢀbutylpyrene for 2.

Interestingly, we recently succeeded in developing the bromide

precursor 1,3,5,9ꢀtetrabromoꢀ7ꢀtertꢀbutylpyrene from 2ꢀtertꢀbutylꢀ

pyrene (1) using ironꢀpowder catalysis.¹⁸We speculated that the

sequence of reactions involved a stepwise bromination process from

the 1ꢀ, 3ꢀ, 5ꢀ, to the 9ꢀposition. In this case, it seemed easy to

understand that the bromination reactions of the pyrene

preferentially occurred at the active sites of the 1ꢀ and 3ꢀpositions

owing to the tertꢀbutyl group protecting the ring against electrophilic

attack at the 6ꢀ and 8ꢀpositions.²²Following this, as expected, the

next step would be to substitute regioselectively at the 5ꢀ and 9ꢀ

positions, which should be favoured given that the bromine atoms

substituted at the 1ꢀ and 3ꢀpositions would sterically hinder the 4ꢀ

and 10ꢀpositions. However, further experimental results revealed

that the reaction process was more complicated than our initial

predictions.

The synthesis of the key intermediate bromopyrenes is shown in

Scheme 2. 1ꢀBromoꢀ7ꢀtertꢀbutylpyrene (2a) and 1,3ꢀdibromoꢀ7ꢀtertꢀ

butylpyrene (2b) have been synthesized with two kinds of

bromination reagents and used to achieve the chemical modifications

of the pyrenes for the required products.²²Firstly, 1) a mixture of 1

and 1.0 equiv. bromine in CH₂Cl₂at 28 °C in the presence of an iron

powder catalyst, afforded 2a in 83% yield; in the other hand, in the

absence of iron powder, mixture of 1 and 1.0 equiv. bromine in

CH₂Cl₂at ꢀ78 °C afforded 2a in 75% yield^22b; 2) A mixture of 1 and

BTMABr₃(1.0 equiv.) in CH₂Cl₂at 28 °C afforded the desired

product 2a in 84% yield. 3) According to reported,^22ba mixture of

Br₂and 1 in anhydrous CH₂Cl₂at ꢀ78 °C afforded 2a in 89% yield in

the absence of iron powder; however, in the presence of iron powder,

a mixture of 1 and 2.0 equiv. of bromine at 28 °C afforded a mixture

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Table 1 Bromination of 2ꢀtertꢀbutylpyrene 1 under the various experimental conditions.^a

Reagents/1

Run

Substrate

Reagents

Products (%)

(mole rate)

1

2

3

4

5

6

7

8

9

Br₂ꢀFe

BTMABr₃

Br₂ꢀFe

BTMABr₃

Br₂

Br₂ꢀFe

1.0

2.0

3.5

3.9

3.0

6.0

2.5

2.9

2a [83]

2a [84]

2a [50], 2b [35]

2b [76]

1

2c [65]

2d (25), 2f (50)^b

2f [84]

2e (70), 2f (30)^b

2e (25), 2f (75)^b

2c

2e+2f

^aThe isolated yields are shown in square bracket. ^bYields were determined by ¹H NMR analysis and shown in parentheses.

2a in 50% yield and 2b in 35% yield. 4) A mixture of 1 and

BTMABr₃(3.5 equiv.) in CH₂Cl₂at 28 °C afforded the desired

product 2b in 76% yield. Similarly, 5) for comparison, we

synthesized 1,3,6ꢀtribromoꢀ7ꢀtertꢀbutylpyrene (2c) in the absence of

iron powder in 65% yield according to the reported procedure.²⁵6)

When 1 was mixed with stoichiometric Br₂(1:3~5) under the same

experimental conditions, the intermediate product 1,3,5ꢀtribromoꢀ7ꢀ

tertꢀbutylpyrene (2d) was obtained with 2f, which could not be

separated from the crude compound by column chromatography. We

attempted to isolate both 2d and 2f in pure form by highꢀ

performance liquid chromatography (HPLC) but failed. 7) When the

same reaction was carried out with 6.0 equiv. of bromine in the

presence of iron powder, the Lewis acidꢀcatalyzed rearrangement of

bromine was observed to give 1,3,5,9ꢀtetrabromoꢀ7ꢀtertꢀbutylpyrene

2f in 84% yield.¹⁸It seems that compound 2f might be formed by the

isomerization of compound 2c under FeBr₃ꢀcatalyzed, which should

be produced from bromine and iron powder present during the

bromination. 8) Reaction of 2c with Br₂(1:2.5) was carried out in the

presence of iron powder. A mixture of bromides 1,3,5,8ꢀtetrabromoꢀ

7ꢀtertꢀbutylpyrene 2e and 1,3,5,9ꢀtetrabromoꢀ7ꢀtertꢀbutylpyrene 2f

was obtained in the ratio of 7:3 (determined by their¹H NMR spectra

analysis); 9) when mixture of 2e and 2f was treated with 2.5 equiv.

of bromine in the presence of iron powder in CH₂Cl₂solution at 28

^oC for 8 h, the expected product, 2f was obtained in 75% yield. 10)

However, attempted isomerization of compound 2e to 2f with other

Lewis acids, such as TiCl₄, AlCl₃or FeCl₃, performed under the

same reaction conditions failed; only the starting compound 2e was

quantitatively recovered. Brominations of compound 1 in the

presence of iron powder to afford the bromoꢀsubstituted pyrene

derivatives 2 were carried out under various reaction conditions and

the detailed results are summarized in Table 1.

Scheme 3. Potential energy surface for 1 and 2. (Gaussian 03W (B3LYP/6–

31G* basis set))

To disclose the bromination mechanism of 1, the deitnsity

functional theory (DFT) calculations DFTꢀcalculated (B3LYP/6ꢀ

31G* basis set) were carried out using the Gaussian 03 software

package for investigating the potentialꢀenergy surface of each

bromopyrene derivative in Scheme 3. B3LYP functional was chosen.

The geometric structures of bromoꢀsubstituted compounds 2 are

optimized at 6ꢀ31G* level and their parameters were given in

supporting information. The frequency and the electronic

distribution of 2 were further tested, the results show that the

vibration frequency of 2 are with positive value, without imaginary

frequency, indicate the calculation of molecular structure energy is

the minimum and stable. The relative free energy (ꢁG₂₉₈) is

exergonic by 7.9 kcal/mol in the process of bromination of 1, leading

to 2a, which can be further bromination to afford 2b and 2c with an

exergonic reaction of 8.2 kcal/mol and 15.4 kcal/mol, respectively.

when 1 with the bromine reagent leads to 2c with an exergonic

reaction of 23.3 kcal/mol. The subsequent bromination step from 2c

or 2d to 2e and 2f with an exergonic is ≈ 8.8 kcal/mol.

Regioselective bromination mechanism of 2-tert-butylpyrene (1)

From previous experimental section, 2a, 2b, and 2c were prepared

that is not depending on the presence of iron (III) bromine, instead,

the stoichiometric ratio of bromine reagent. This process is classical

electrophilic substitution reaction. This result is strongly attributed to

the high reactivity of the 1ꢀ, 3ꢀ, 6ꢀ and 8ꢀpositions in the pyrene ring.

However, in the following bromination reactions for 2d, 2e and the

role played by the FeBr₃ꢀinduced rearrangement to form the 2f is not

clear.

when 1 with the bromine reagent leads to 2c with an exergonic

reaction of 23.3 kcal/mol. The subsequent bromination step from 2c

or 2d to 2e and 2f with an exergonic is ≈ 8.8 kcal/mol.

Comparison of the geometric structures of 2, that show that the

angle of bromine atom in 6ꢀposition of 2c (∠Br3ꢀC5ꢀC6 = 115.5^o) or

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8ꢀposition of 2e (∠Br4ꢀC8ꢀC7 = 115.7^o), which is less than in other suggest that compounds 2c, 2d and 2e were the intermediates for the

bromo substitutedꢀposition (for example: ∠Br1ꢀC1ꢀC2 = 120.6 in formation of the 1,3,5,9ꢀtetrabromoꢀ7ꢀtertꢀbutylpyrene 2f.

2a). And the tertꢀbutyl group located at 7ꢀposition of pyrene core

In this reaction, Iron powder leads to titled products where

have slightly crowded in 2c and 2e with angle of 125.7^o± 0.1, which bromine is directed to the Kꢀregion (positions 5ꢀ and 9ꢀ) instead of

is larger than those in 1 and 2a–b, 2d and 2f. Interesting thing is that the more reactive positions 6ꢀ and 8ꢀ. There are two reasons can

2c or 2d was generated from 2b with similar exergonic (7.2 kcal/mol explain this phenomenon of FeBr₃ꢀinduced intramolecular bromine

for 2c and 7.7 kcal/mol for 2d). However, the 2d can not observed rearrangement: one possible reason is a release of steric hindrance is

by bromination 2b with an excess of bromine without iron powder indicated as the driven force for this rearrangement, which is also

presenting in our experiment. In fact, in the presence of iron (III) possible in the absence of FeBr₃where no rearrangement is observed.

bromide, 2a–c and 2e was synthesized by undergo FriedelꢀCraftsꢀ Another possible reason from DFTꢀcalculation is lowing the

type reactions from 1 with bromine. From Scheme 3, the presence of activation energy of the rearrangement induced by FeBr₃.

iron (III) bromide might be contribute to lower the activation energy

of bromination and induce intramolecular bromine rearrangement in

the process of 2d and 2f, that bromine atom would shift from active

site (6ꢀ or 8ꢀposition) to Kꢀregion (5ꢀ or 9ꢀposition).

Scheme 5. Synthetic route for compound 3 via a SuzukiꢀMiyaura crossꢀ

coupling reaction, reagents and conditions: a) 4ꢀmethoxylphenylboronic acid,

[Pd(PPh₃)₄], Na₂CO₃, toluene/EtOH, 24 h, 90 °C.

In order to further investigate bromoꢀsubstitution positions of the

pyrene in more detail, a series of arylꢀsubstituted pyrenes (3) were

prepared from the resultant bromopyrenes using 4ꢀ

Scheme 4. Possible regioselective bromination mechanism of 1

methoxyphenylboronic acid via

a Pdꢀcatalyzed crossꢀcoupling

The possible bromination reaction pathway has been summarized

in Scheme 4. Firstly, The relatively easy electrophilic substitution at

the orthoꢀposition to a tertꢀbutyl group (6ꢀ or 8ꢀposition) on the

pyrene ring is remarkable because usually the steric bulkiness of a

tertꢀbutyl group might be expected to direct the substitution towards

other positions of the pyrene ring.^7,8This result is strongly

attributable to the high reactivity of the 1ꢀ, 3ꢀ, 6ꢀ and 8ꢀpositions of

the pyrene ring. Second, however, the pyrene exhibit special

electronic structure that the Kekulé structure (I, II and III) show the

greatest number of benzenoid rings should have the greatest weight

in the superposition diagram, meanwhile, also show the greatest

number of double bonds in the “exposed” position have the greatest

weight (see supporting information).²⁶So, when the bromide

attracted the 6ꢀposition of 2b, due to the steric strain involving the

tertꢀbutyl group and lowing the Gibbs free energy, the bromide

would rearrange to 5ꢀposition under FeBr₃ꢀcatalyzed and afford 2c.

Similarly, the tetrabromide 2f was obtained by the same FeBr₃ꢀ

catalyzed rearrangement in the bromination of tribromopyrenes 2c

and 2d in the presence of iron powder. The above results strongly

reaction. Using the 4ꢀmethoxylphenyl group as an effective

substituent, several different shaped pyrenes 3 were synthesized and

are displayed in Scheme 5: 7ꢀtertꢀbutylꢀ1ꢀ(4ꢀmethoxyphenyl)pyrene

(3a), 7ꢀtertꢀbutylꢀ1,3ꢀbis(4ꢀmethoxylphenyl) pyrene (3b),^22a7ꢀtertꢀ

butylꢀ1,3,6ꢀtris(4ꢀmethoxyphenyl)pyrene (3c), 7ꢀtertꢀbutylꢀ1,3,5ꢀtrisꢀ

(4ꢀmethoxylphenyl)pyrene (3d), 7ꢀtertꢀbutylꢀ1,3,5,8ꢀtetrakis(4ꢀ

methoxyphenyl)pyrene (3e) and 7ꢀtertꢀbutylꢀ1,3,5,9ꢀtetrakis(4ꢀ

methoxyl)phenylpyrene (3f)¹⁸. The molecular structure of all

compounds was characterized by their H/¹³C NMR spectra, singleꢀ

1

crystal Xꢀray diffraction, FTꢀIR spectroscopy, mass spectrometry, as

well as by elemental analysis. All analysis results herein on the arylꢀ

substituted pyrene 3 strongly supported our previous predictions.

The performance of the organic compounds in optoelectronic

devices strongly relies on the molecular packing and

intra/intermolecular interactions in the solidꢀstate. Therefore,

investigating the effects of a structureꢀproperty relationship between

the substituent groups on the pyreneꢀcore using crystal structure and

photophysical

properties

is

significant

for

organic

electroluminescence materials. Herein, we expected that the

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integration of polyꢀmethoxylphenyl groups with the pyrene core in a mixture of dichloromethane and hexane (1:2, v/v). The singleꢀcrystal

molecular structure might influence the crystal packing, leading to Xꢀray structure is depicted in Figure 2. It can be seen that the 4ꢀ

favourable optical features and chargeꢀtransport properties that could methoxyphenyl groups in this molecule form a torsion angle (65.43

be useful in optoelectronic devices.

(17)°) with the plane of the centeral pyrene ring to prevent faceꢀto

face πꢀstacking and steric clashes between ortho H atoms on the

phenyl ring and those at the 3ꢀ and 9ꢀpositions. An interesting

feature of the compound in the solidꢀstate is that there is an

intermolecular C–H···π interaction (C19–H19···C3 = 2.88 Å, C21–

Description of crystal structures

Previously, we reported that several Yꢀshaped arylꢀsubstituted

pyrenes with electronꢀdonating/withdrawing groups at the paraꢀ

position of the C₆H₄rings inefficiently impact on the molecular

packing in the solidꢀstate.^22aKonishi et al. have validated that alkyl

groups located at the 1ꢀ, 3ꢀ, 6ꢀ, and/or 8ꢀpositions of the pyrene ring

play significant roles in tuning the photophysical properties.¹⁵Herein,

this article presents a series of positionꢀsubstituted pyrenes that not

only take place of the active sites (1ꢀ, 3ꢀ, 6ꢀ and 8ꢀpositions) but also

the Kꢀregion (4ꢀ and 9ꢀpositions) of pyrene, and allow us to shed

light on the effect of multiple 4ꢀmethoxylphenyl groups on the

molecular packing and optical physical properties.

H21···C7

= 2.85 Å, C23–H23···C13 = 2.88 Å) between

neighbouring molecules. These interactions led to a comparatively

large twist angle between the pyrene core and the methoxylphenyl

fragment, and effectively suppress the formation of the πꢀπ stacking.

On increasing the numbers of 4ꢀmethoxylphenyl groups and

substituting at different positions in the pyrene derivatives 3a→f, the

space groups (orthorhombic for 3a, monoclinic for 3b, 3c and 3e,

triclinic for 3d and 3f) became more asymmetric. It can be seen that

the torsional angles between the 4ꢀmethoxyphenyl group and the

pyrene core decreased from 65.43 (17)° to 48.08 (18)°. With the

number of substituted group increasing, the conformation molecules

trend for increasing coꢀplanarity.²⁷However, without the tertꢀbutyl

group located at the nodal planes involving the 2ꢀ/7ꢀpositions in

1,3,6,8ꢀtetrakis(4ꢀmethoxyphenyl)pyrene (4),¹⁸the torsion angle is

unexpectedly larger than 3 and is up to 76.1 (4)°.

Figure 1. Xꢀray structures of compounds 3.

Crystals of 3 suitable for Xꢀray structure analysis were grown

from mixed solvents via slow evaporation at room temperature. And

the key crystallographic data are summarized in supporting

information Table S2; the crystal structures of molecules for 3 are

shown in Figure 1.

Figure 3. Crystal packing in 3c by C–H···π interactions

Colourless rod crystals of 3c suitable for Xꢀray diffraction were

recrystallization from a mixture of dichloromethane and methanol by

slow evaporation at room temperature. Figure 3 shows the crystal

packing in 3c. The crystal structure revealed the novel asymmetric

substitution of the pyrene core. As expected, the 4ꢀmethoxyphenyl

group successfully substituted at the 6ꢀposition of the pyrene with

anapproximately perpendicular torsion angle of 88.58(4)°. In the

crowded region at the 6ꢀ and 7ꢀpositions two bulky moieties were

introduced, which contact each other by steric interaction. This

causes twoꢀfold tertꢀbutyl group disorder with occupancy ratio 0.634

(12):0.366 (12) for C18, C19 and C20 and an intramolecular short

contact (C18–H18B···C26 = 2.81 Å) and significant distortion for

the Csp²hybridization with an angle of 123.81(15)° at C4–C5–C17.

In the offꢀset packing system of 3c, the two proximal pyrene

molecular planes have a long centroidꢀcentroid distance of 7.97 Å

and no π···π stacking was observed. The adjacent molecules

interacted by a classical C–H···π bond (C34–H34···C1 = 2.84 Å,

C32–H32···C15 = 2.82 Å, C23–H23···C10 = 2.84 Å). It seems that

the close proximity of the 4ꢀmethoxyphenyl moiety and the tertꢀ

butyl group caused strong intermolecular steric hindrance in this

packing system.

Figure 2. Crystal packing of 3a by CꢀH···π interactions

Colourless crystals of compound 3a suitable for Xꢀray

crystallographic analysis were obtained by crystallization from a

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Table 2. The photophysical and electrochemical properties of compounds 3, 4 and 5.

[h]

τ

T_m^[g]/T_d

λ

_maxabs (nm)

λ_maxPL (nm)

Φ_f^[c]

HOMO

(eV)

Energy gap

(eV)

Compounds

(ns)^[a]

(^°C)

Solns^[a]/films^[b]

391, 407 nd

solns/films

0.41 / nd

347

363

nd

372

–5.06^[d]/ nd

3.65^d(3.30)^[f]8.6

141 / 282

167 / 173

249 / nd

240 / 399

330 / 410

271 / nd

nd / 433

3a

3b

3c

3e

3f

4

402

406

420

421

434

450 0.56 / 0.58

471 0.71 / 0.28

441 0.76 / 0.58

443 0.90 / 0.72

488 0.94 / nd

–4.93 / –5.44^[e]3.51 (3.17)

8.9

5.2

2.2

5.8

1.9

18.8

363, 375 381

–4.84 / –5.06

–4.76 / –5.36

–4.76 / –5.37

–4.71 / nd

3.46 (3.13)

3.37 (3.03)

3.40 (3.03)

3.24 (2.94)

3.70 (3.31)

381

379

391

388

369

405

343, 356 357

411, 433 414 0.24 / 0.17

–4.93 / nd

5

^[a]Measured in dichloromethane at room temperature. ^[b]Measured in thin films.^[c]Measured in dichloromethane and in thin films, respectively.

[d]

[e]

onset [f]

Calculation by DFT (B3LYP/6–31G*).

Calculated from Onset of first oxidation potential according to equations: ꢀ(4.8+E_ox

)

Estimated from UVꢀvis absorption spectra in solution. ^[g]Melting temperature (T_m) obtained from differential scanning calorimetry (DSC)

measurement. ^[h]Decomposition temperature (T_d) obtained from thermogravimetric analysis (TGA). nd. No determination.

Yellow needles of 3d were obtained from a mixed solution of close to each other. Also, the 4ꢀmethoxyphenyl group and bulky tertꢀ

dichloromethane/hexane = 1:1; the asymmetric unit of compound 3d butyl group share a crowded space at the 1ꢀ and 2ꢀpositions of the

contains one molecule (Figure 4). The molecule exhibits a nonꢀ pyrene, and these sterics result in the Csp²hybridization angle C4–

planar and the central pyrene ring has a slight bend; possibly arising C5–C17 changing to 124.07(6)° via intramolecular hydrogen bonds

from the imbalance of the electrostatic potential on the molecular (C19–H19B···C26 = 2.56 Å, C18–H18B···C22 = 2.53 Å).

surface.²⁷The interꢀplanar angles between the central pyrene

coreand the outer substituent phenyl rings range from 44.2(5)° to

57.7(5)°. The crystal structure was arranged in columns along the

aaxis, through essentially parallel, or nearꢀparallel interactions

between translationally equivalent molecules. Each molecule is

interlaced with adjacent columns along the aꢀaxis by the formation

of π–π stacking with a centroidꢀtoꢀcentroid distance of 4.07 Å and

interꢀplanar angle of 0°. There are numerous C–H···π interactions

formed between phenyl hydrogens and neighbouring aromatic rings.

Figure 5. (a) Crystal packing in 3e by C–H···π interactions

Comparison of tetraꢀsubstituted pyrenes 3e, 3f and 1,3,6,8ꢀ

tetrakis(4ꢀmethoxyphenyl)pyrene (4), the crystal packing in the

solidꢀstate is different attribute to the positionꢀsubstituted

diversification.^18,28For the packing structures of 3a to 3f, the Xꢀray

diffraction revealed that the torsion angle decreased between the

substituent group and the pyrene core as well as the molecular

packing varied significantly from 3D (column structure) to 2D

Figure 4. Crystal packing in 3d by C–H···π interactions

(planar structure) with the number of 4ꢀmethoxylpehnyl groups

increased. As mentioned above, the number of substituent groups

and their positions, as well as the bulky tertꢀbutyl groups play an

important role in arranging the molecular conformations. The

structures became more planar, which in turn was beneficial for πꢀ

conjugation and improved the optical density, leading to strong FL

emission in the solidꢀstate.²⁹In the next section, we discuss the

Compound 3e was dissolved in CHCl₃and kept in a CH₃OH

atmosphere at room temperature to afford orange single crystals

suitable for Xꢀray diffraction. The crystal system of 3e is monoclinic

with space group P2₁/c and is shown in Figure 5. A similar

arrangement pattern to 3d was observed. The molecules also adopt

aslipped faceꢀtoꢀface and π–π stacking pattern along the bꢀaxis with

resulting photophysical properties resulting from the presence of

acentroidꢀtoꢀcentroid distance of 4.96 Å. This is longer than that

multiple 4ꢀmethoxylphenyl substituents.

observed in 3d, arising from an extra 4ꢀmethoxyphenyl moiety

playing a role to prevent the neighbouring molecules getting too

Photophysical properties

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The normalized UVꢀvis absorption and fluorescence spectra for 3

a

significant redꢀshift in comparison with those of the

recorded in dichloromethane are shown in Figure 6, For comparision, tetrasubstituted derivatives 3e and 3f, which is probably a result of

1,3,6,8ꢀtetrakis(4ꢀmethoxyphenyl)pyrene (4)¹⁸and 2ꢀtertꢀbutylꢀ the nodal planes passing through the 2,7ꢀpositions, leading to a

4,5,7,9,10ꢀpentakis(4ꢀmethoxyphenyl)pyrene (5)^17awere also lower electronic density by the rotation of 4ꢀmethoxyphenyl group

summarized in here for investigating the effect of the positionsꢀ located at 7ꢀposition of pyrene core. This suggests the 2,7ꢀ

dependent arylꢀfunctionalized pyrene derivatives for the packing substitutions have a small influence on the electronic interaction,²

structures and photophysical properties, and the corresponding and the results have also been reinforced by DFT calculations

photophysical data is summarized in Table 2. Except for 3c and 5, all (mentioned below).

molecules exhibited very similar photophysical characteristics with

For the emission spectra, all compounds exhibit intense emissions

wellꢀresolved spectral bands in both the shortwavelength of 283−305 in the blue region (391–434 nm). The emission maxima of 3 and 4

nm and long wavelength of 347–391 nm regions. The absorption are bathochromically shifted depending on the numbers of 4ꢀ

spectra of 3→4 show a maximum band at 347 nm for 3a, 363 nm for methoxylphenyl units, revealing an identical trend to their absorption

3b, 363 nm for 3d, 381 nm for 3e, 381nm for 3f and 391 nm for 4. spectra. No characteristic excimer fluorescence was observed in any

However, 3c has two absorption peaks centered at 295 nm and 375 of the spectra. It is worth noting that 1,3,5,8ꢀfunctionalized pyrene

nm with a shoulder peak at 363 nm; similarly, 5 displays two 3e exhibits an emission with λ_emvalues of 420 nm, which almost

maxiumn absorption peaks at 296 nm and 356 nm with a shoulder overlaps with the emission spectrum (421 nm) of 1,3,5,9ꢀ

peak at 343 nm. Clearly, both the number of substituents and the functionalized pyrene (3f). In general, the substitution pattern of the

substitution position (pathway) strongly influence the electronic pyrene moiety has

a substantial effect on the fluorescence

absorption;²the absorption maximum of 3 revealed a remarkable wavelength, and the effect of being substituted at the active 1ꢀ, 3ꢀ, 6ꢀ

redꢀshift. It is thought that such phenomena arise from the increasing and 8ꢀpositions for the S₁←S₀excitations is more significant than at

number of peripheral arms in this series, which extend the πꢀ the Kꢀregion (4ꢀ, 5ꢀ, 9ꢀ and 10ꢀpositions).²

conjugation of the pyrenes.

In the case of 3e and 3f, smaller redꢀshifts in their electronic

absorption profiles indicate that the structural changes and/or

electronic distribution changes can cause an electronic

communication missing in the pyrene cores.³⁰For 5, a deepꢀblue

emission was observed with a maximum peak at 411 nm and a

shoulder at 430 nm in solution.

Figure 6. (a) Normalized UVꢀvis absorption and (b) emission spectra of

compounds 3, 4 and 5 recorded in dichloromethane at ca. ~10^–5–10^ꢀ6M at

25 °C.

The longest absorption (λ_max) exhibited by 3e and 3f was

approximately red shifted by ca. 34 nm versus 3a, indicating the

HOMO−LUMO energy gap of 3 decreased on increasing the

conjugation length. Interestingly, for the handꢀshaped compound 5,

Figure 7. (a) Normalized UVꢀvis absorption and (b) emission spectra of 3

despite it having the most substituents, the absorption does not show and 5 in thin films.

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The UVꢀvis absorption and emission spectra of selected pyrenes greater for the HOMOs than for the LUMOs with a sizable shrinking

in the solidꢀstate are shown in Figure 7, and the optical data are of the HOMO−LUMO gap by 0.28 eV with respect to 3a, which is

summarized in Table 2. Compared with the corresponding solutions, in good agreement with the experimentally measured results in

the absorption for 3b, 3c, 3e, 4 and 5 films reveals a slight redꢀshift tendency, the slight different to those obtained by UVꢀvis absorption

(about 10 nm) (Table 2). However, the absorption of 3f as a film (ꢁE_{gap opt}= 0.27 eV) owing to the DFTꢀcalculation was performed in

shows a slight blueꢀshift in comparison with that in solution. This the gas phase.

unusual blueꢀshift might be due to the different dielectric constant.³¹

The emission maxima of 3b, 3e and 3f as thin films exhibited redꢀ

shifts of less than 48 nm relative to those in solution, and the

compound 3c exhibits a redꢀshift of 65 nm (from 406 nm to 471 nm).

(Table 2). On increasing the numbers of 4ꢀmethoxylphenyl moieties,

the redꢀshift decreased in the following order: 5 (3 nm) < 3f (22 nm)

≈ 3e (21 nm) < 3b (48 nm) < 4 (54 nm) < 3c (65 nm), indicating the

positionsꢀsubstitution of arylꢀfunctionalized would influence the

electronic interaction. Owing to the strong intermolecular

interactions in the thin film of 3c and 4, the emission maxima

exhibited a greater redꢀshift as a thin film state with high noise

level.³²

Figure 8. Computed molecular orbital plots (B3LYP/6–31G*) of compounds

Different to the 1,3,6,8ꢀtetrakis(4ꢀmethoxyphenyl)pyrene 4,¹⁸that

of 3 and 5; the upper plots represent the HOMOs, and the lower plots

tends to exhibit a high noise level PL spectrum in the solidꢀstate. the

represent the LUMOs

.

tetraꢀsubstituted pyrenes 3e and 3f exhibited clear and sharp

emission peaks in the blueꢀregion without extra excimer emissions in

the solidꢀstate owing to the bulky tertꢀbutyl group located at 7ꢀ

position of the pyrene ring suppressing the aggregation. Compound

4 also presents a very high fluorescence quantum yield (Φ_f^c) of the

range of ~0.94 in solution.

For comparison, the quantum yields of 3b, 3c, 3e and 3f in the

solidꢀstate were also investigated (0.58 for 3b, 0.28 for 3c, 0.58 for

3e and 0.72 for 3f). However, for 5, low fluorescence quantum

yields in both solution and the solidꢀstate were obtained due to

energy loss that is likely occurring during the exciton migration.³³

The fluorescence lifetime of 3aꢀc, 3e, 3f, 4 and 5 are 8.6 ns, 8.9 ns,

5.2 ns, 2.2 ns, 5.8 ns, 1.9 ns, 18.8 ns, respectively. Excellent optical

features were obtained in these compounds, which make them of

potential use in new optoelectronic devices, such as blue emitters in

OLEDs, or as models for further exploring a new generation of

organic materials based on pyrene.

Compared with 3e/3f and 4, the presence of the tertꢀbutyl group at

the 7ꢀposition, could lead to a lower energy gap by lowing the

molecular LUMOs. With the number of substituent groups increased,

from the monoꢀsubstituted 3a to the tetraꢀsubstituted pyrenes 4 and

3e/3f, the energy gap of the representative molecules decreased.

Especially, the speical electronic structure of pentaꢀsubstituted

pyrene 5 inhibits absorption spectra is different from others, due to

the substituted group at the Kꢀregion (4,5,9,10ꢀpositions) in favour

of blueꢀshift by the improving energy gap of the molecular structure;

when as the 4ꢀmethoxyphenyl group located at nodal planes would

weak electronic coupling with entire pyrene,^[4]attributing to little

influence on S₂←S₀absorption but lager influence on S₁←S₀

absorption.³⁴So, These conclusions are also consistent with our

quantum chemical calculations.

Electrochemistry

The electrochemical properties of selected compounds 3 were

investigated in CH₂Cl₂solution by cyclic voltammetry (CV) in a

threeꢀelectrode electrochemical cell with Bu₄NClO₄(0.1 M) and

Ag/AgCl as electrolyte and reference electrode respectively, and

using ferrocene (Fc/Fc⁺) as the internal standard with a scan rate of

100 mVs⁻¹at room temperature.

As shown in Figure 9, compound 3b exhibits a quasiꢀreversible

oxidation processin the positive potential region with a oxidation

process around 1.0 V (vs. Ag/AgCl), and compounds 3c, 3e and 3f

exhibit two reversible or quasiꢀreversible oxidation processes,

respectively. On the basis of the absorption spectra and the CV, the

corresponding HOMO and LUMO energy levels were confirmed and

the results are displayed in Table 3 and in the supporting information

(Table S3). The HOMO values were calculated from the oxidation

potential by the empirical formulae HOMO = –(4.8+E_ox^onset), where

E_oxis the onset of the oxidation potential. The HOMO values were –

5.44 eV for 3b, –5.06 eV for 3c, –5.35 eV for 3e and –5.36 eV for 3f.

The LUMO levels were determined from the HOMO and energy gap.

Quantum chemistry computation

To gain further insight into the effect of multiꢀsubstituents and

pathways on the electronic structure and spectral properties of

compounds 3, 4 and 5, quantum chemical calculations were

calculated using DFT methods at the B3LYP/6–31G* level. The

calculated energies of the frontier molecular orbitals are presented in

Figure 8 and in the supporting information.

Scrutiny of the electronic structures reveals that both HOMOs and

LUMOs of 3 were primarily delocalized over the entire pyrene

component, as well as slightly in the peripheral phenyl moiety, the

only difference being in the energy of these frontier molecular

orbitals, which in turn relied on the system architecture. For instance,

on increasing of the numbers of the substituents from 3a to 3f, the

HOMO values are more posotive varied from –5.06 eV (3a) to –4.76

(3f) eV, the increased positionsꢀdependent substitution resulted in a

lowering of both the HOMOs and LUMO by 0.3 eV and 0.05 eV,

respectively. Obviously, The effects of multiple substituents is

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For 3b and 3c containing increasing numbers of 4ꢀmethoxyphenyl thermal stabilities, making such molecules potential candidates in

moieties in different positions on the pyrene, similar energy gap optoelectronic applications such as OLEDꢀlike devices. Further

(3.17 eV for 3b and 3.13 eV for 3c) with different HOMO and investigations on their usefulness in organic electroluminescent

LUMO levels are achieved.

devices are in progress in our laboratory.

Experimental Section

Materials: Unless otherwise stated, all other reagents used were

purchased from commercial sources and used without further

purification. The preparations of 2ꢀtertꢀbutylpyrene (1)³⁵was

reported previously.

1

All melting points (Yanagimoto MPꢀS₁) are uncorrected. H/¹³C

NMR spectra (300 MHz) were recorded on a Nippon Denshi JEOL

FTꢀ300 NMR spectrometer. IR spectra were measured for samples

as KBr pellets in a Nippon Denshi JIRꢀAQ2OM spectrophotometer.

Mass spectra were obtained with a Nippon Denshi JMSꢀHX110A

Ultrahigh Performance Mass Spectrometer at 75 eV using a directꢀ

inlet system. Elemental analyses were performed by Yanaco MTꢀ5.

UV/ Vis spectra were obtained with a Perkin–Elmer Lambda 19

UV/Vis/NIR spectrometer in various organic solvents. Fluorescence

spectroscopic studies were performed in various organic solvents in

a semimicro fluorescence cell (Hellma^®, 104FꢀQS, 10 × 4 mm, 1400

ꢂL) with a Varian Cary Eclipse spectrophotometer. Fluorescence

quantum yields were measured using absolute methods.

Thermogravimetric analysis (TGA) was undertaken using a SEIKO

EXSTAR 6000 TG/ DTA 6200 unit under nitrogen atmosphere at a

heating rate of 10 °C min⁻¹. Differential scanning calorimeter (DSC)

Figure 9. Cyclic voltammograms recorded for selected compounds 3.

Additionally, 3e and 3f have same numbers of substituents but

different substituted position, that also showed similar HOMO (–

5.36 eV for 3e and –5.37 eV for 3f, respectively) and LUMO (–2.33

eV for 3e and –2.34 eV for 3f, respectively). From both Figure 9 and

Table S2, it can be seen that oxidation potential are shifted to more

positive values when increasing the number of substituents. The

halfꢀwave potentials for compounds 3b (2 substituents), 3c (3

substituents), 3e (4 substituents) and 3f (4 substituents) are 1.45 eV,

1.51 eV, 1.64 eV and 1.67 eV, respectively. Furthermore, the

reduction potentials was effected dependent on position, and

substituted at active sites of 1,3,6,8ꢀposition would lower LUMO

level and Kꢀregion of 4,5,9,10ꢀposition contributes to improve

LUMO level.

was performed using

a Perkin–Elmer Diamond DSC Pyris

instrument under nitrogen atmosphere at a heating rate of 10 °C

min⁻¹. Photoluminescence spectra were obtained using a FluroMaxꢀ2

(JobinꢀYvonꢀSpex) luminescence spectrometer. Electrochemical

properties of HOMO and LUMO energy levels were determined by

Electrochemical Analyzer. The quantum chemistry calculation was

performed on the Gaussian 03W (B3LYP/6–31G* basis set)

software package.³⁶

Synthesis of 2-tert-butylpyrene (1). A mixture of pyrene (5 g, 24.2

mmol) and 2ꢀchloroꢀ2ꢀmethylpropane (2.62 g, 3.23 mL) was added

in 40 mL of CH₂Cl₂at 0 °C and stirred for 15 min. Powdered

anhydrous AlCl₃(3.62 g, 27.2 mmol) was slowly added to a stirred

solution. The reaction mixture was continuously stirred for 3 h at

28 °C and the reaction process was tracked by GC, then poured into

a large excess of ice/water. The reaction mixture was extracted with

CH₂Cl₂(2 × 50 mL). The combined organic extracts were washed

with water and brine, dried with anhydrous MgSO₄and evaporated.

The residue was crystallized from hexane to afford pure 2ꢀtertꢀ

Conclusions

In summary, the bromination mechanism of pyrene was explored by

experimental methods. Clear evidence was observed for

theformation of monoꢀ to tetrakis(4ꢀmethoxyphenyl)ꢀsubstituted

pyrenes (3), which were synthesized by SuzukiꢀMiyaura crossꢀ

coupling reaction of the corresponding bromopyrenes with 4ꢀ

methoxyphenyl boronic acid, and characterized by singleꢀcrystal Xꢀ

ray diffraction, H/¹³C NMR spectra, mass spectrometry as well as

1

elemental analysis. These results supported our conclusions on the

bromination mechanism, namely that it was possible to

regioselectively generate the monoꢀ to tetrabromopyrenes from the

2ꢀtertꢀbutylpyrene (1) via a stepwise electrophilic substitution using

a FeBr₃ꢀcatalyzed rearrangement. Otherwise, the spectroscopic data,

DFT calculations and electron chemistry results of the arylꢀ

functionalized pyrenes indicate that the HOMOs and LUMOs level

can be tuned by both the number of substitution and substutitedꢀ

position cooperativity; the numbers of substituent moieties

contribute to higher oxidation potential and the reduction potential

was attributed to positionꢀsubstituted. The series of new molecular

materials combines excellent optical features with reasonable

butylpyrene (2) in 71% yield (4.56 g) as

a gray powder.

Recrystallization from hexane gave 2 as colourless prisms. Mp:

111.5–113.2 °C (lit.³⁵Mp: 110–112 °C). The ¹H NMR spectrum

agreed with the reported values. ¹H NMR (300 MHz, CDCl₃): δ

(TMS, ppm) 1.59 (s, 9H, tBu), 8.18 (d, J = 9.2 Hz, 2H, pyreneꢀH),

8.30 (s, 2H, pyreneꢀH), 8.37 (d, J = 9.2 Hz, 2H, pyreneꢀH), 8.47 (s,

1H, pyreneꢀH).

Synthesis of 1-bromo-7-tert-butylpyrene (2a).

Run 1: Lewis acid-catalysed bromination of 2-tert-butylpyrene

A mixture of 2ꢀtertꢀbutylpyrene (1) (0.26 g, 1 mmol) and iron

powder (0.56 g, 10 mmol) were combined in CH₂Cl₂(10 mL) at

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0 °C with stirring for 30 min. A solution of Br₂(0.051 mL, 1 mmol) ppm) 1.59 (s, 9H, tBu), 8.15 (d, J = 9.2 Hz, 2H, pyreneꢀH), 8.30 (s,

in CH₂Cl₂(10 mL) was slowly added dropꢀwise with vigorous 1H, pyreneꢀH), 8.47 (d, J = 9.2 Hz, 2H, pyreneꢀH), 8.47 (s, 1H,

stirring. After this addition, the reaction mixture was continuously pyreneꢀH). FABꢀHRMS: m/z calcd. for C₂₀H₁₆Br₂416.2; found

stirred for 5 h at 28 °C. The mixture was quenched with Na₂S₂O₃417.4 [M⁺]. Anal. Calcd for C₂₀H₁₆B₂: C, 55.72; H, 3.88; found: C,

(10%) and extracted with CH₂Cl₂(20 mL × 2). The combined 55.05; H, 4.56.

organic extracts were washed with water and brine and evaporated. Run 5: Synthesis of 1,3,6-tribromo-7-tert-butylpyrene (2c)²⁵

The crude product was a brown colour, and the residue was 2ꢀtertꢀButylpyrene (1) (1.3 g, 5.03 mmol) was dissolved in CH₂Cl₂

recrystallized from a mixted solution of tolueneꢀhexane (1:2) to give (20 mL) and stirred for 30 min. at 25 °C. To this solution was added

pure 1ꢀbromoꢀ7ꢀtertꢀbutylpyrene (2a) in 83% yield (290 mg) as a Br₂(1 mL, 19.4 mmol) and violently stirred for 24 h. The reaction

white powder.

Run 2:

mixture was poured into iceꢀwater (50 mL) and neutralized with an

solution of benzyltrimethylammonium tribromide aqueous 10% Na₂S₂O₃solution, the mixture was extracted

A

(BMTABr₃) (7.57 g, 19.4 mmol) in dry CH₂Cl₂(50 mL) was slowly withCH₂Cl₂(2 × 50 mL), and the organic layer was washed with

added to a solution of 2ꢀtertꢀbutylpyrene (1) (5 g, 19.4 mmol) in dry brine and evaporated. The residue was recrystallized from a mixed

CH₂Cl₂(150 mL) at 0 °C under a nitrogen atmosphere. The resulting solution of CH₂Cl₂ꢀhexane (2:1) to afford 1,3,6ꢀtribromoꢀ7ꢀtertꢀ

mixture was allowed to slowly warm up to 28 °C and stirred butylpyrene(2c) in 65% yield (1.6 g). Mp: 276–277 °C. The ¹HNMR

overnight. The reaction mixture was quenched with Na₂S₂O₃and spectrum completely agreed with the reported values.^{25 1}H NMR

extracted with CH₂Cl₂(2 × 50 mL). The combined organic extracts (300 MHz, CDCl₃): δ (TMS, ppm) 1.81 (s, 9H, tBu), 8.08 (d, J= 9.2

were dried with anhydrous MgSO₄and evaporated. The residue was Hz, 1H, pyreneꢀH), 8.10 (s, 1H, pyreneꢀH), 8.34 (d, J = 8.58Hz, 1H,

crystallized from hexane to give pure 1ꢀbromoꢀ7ꢀtertꢀbutylpyrene pyreneꢀH), 8.39 (d, J = 9.7 Hz, 1H, pyreneꢀH), 8.46 (s, 1H, pyreneꢀ

1

(2a) in 84% yield (5.5 g) as white crystals. The H NMR spectrum H), 8.85 (d, J = 9.7 Hz, 1H, pyreneꢀH). FABꢀHRMS: m/z calcd. for

completely agreed with the reported values.^{22b 1}H NMR (300 MHz, C₂₀H₁₅Br₃495.05; found 494.0 [M⁺]. Anal. Calcd for C₂₀H₁₅Br₃: C,

CDCl₃): δ (TMS, ppm) 1.59 (s, 9H, tBu), 7.99 (d, J = 8.2 Hz, 1H), 48.52; H, 3.05; found: C, 49.32; H, 4.55.

8.01 (d, J = 8.79 Hz, 1H), 8.08 (d, J = 9.0 Hz, 1H), 8.17 (d, J = 10 Run 6: Lewis acid-catalyzed bromination of 2-tert-butylpyrene

Hz, 1H), 8.20 (d, J = 8.22 Hz, 1H), 8.27–8.27 (m, 2H), 8.40 (d, J = A mixture of 2ꢀtertꢀbutylpyrene (1) (0.26 g, 1 mmol) and iron

9.0 Hz, 1H). FABꢀHRMS: m/z calcd. for C₂₀H₁₇Br 337.3; found powder (0.56 g, 10 mmol) were added to CH₂Cl₂(10 mL) at 0 °C

335.9 [M⁺]. Anal. Calcd for C₂₀H₁₇Br: C, 71.23; H, 5.08; found: C, with stirring for 30 min. A solution of Br₂(0.153 mL, 3 mmol) in

72.25; H, 6.33.

Synthesis of 1,3-dibromo-7-tert-butyl-pyrene (2b)

CH₂Cl₂(10 mL) was slowly added dropꢀwise with vigorous stirring.

After this addition, the reaction mixture was continuously stirred for

Run 3: A mixture of 2ꢀtertꢀbutylpyrene (1) (0.26 g, 1 mmol) and 5 h at 28 °C. The mixture was quenched with Na₂S₂O₃(10%) and

iron powder (0.56 g, 10 mmol) were added in CH₂Cl₂(10 mL) at extracted with CH₂Cl₂(2 × 20 mL). The combined organic extracts

0 °C with stirring for 30 min. A solution of Br₂(0.105 mL, 2 mmol) were washed with water and brine and evaporated. The crude

in CH₂Cl₂(10 mL) was slowly added dropꢀwise with vigorous product was washed with hot hexane to afford mixture of white

stirring. After this addition, the reaction mixture was continuously compounds 2d and 2f (430 mg), the mixture is difficult to separate

1

stirred for 5 h at 28 °C. The mixture was quenched with Na₂S₂O₃by common chromatography. The yield was evaluated by H NMR

(10%) and extracted with CH₂Cl₂(20 mL × 2). The combined spectral analysis (25% for 2d, 50% for 2f). The product cannot

organic extracts were washed with water and brine and evaporated. further been separated by Highꢀspeed Counterꢀcurrent

The crude product was black in colour. The residue was washed with Chromatography (HSCCC) and was used as a mixture for the Suzuki

1

hot hexane and filtered to afford 1,3ꢀdibromoꢀ7ꢀtertꢀbutylpyrene coupling reactions. H NMR (300 MHz, CDCl₃) for 2d: δ (TMS,

(2b) 146 mg (35%). The solution was evaporated and recrystallized ppm) 1.64 (s, 9H, tBu), 8.79 (s, 2H, pyreneꢀH), 8.86 (d, J = 9.8 Hz,

from a mixed solution of CH₂Cl₂ꢀhexane (1:2) to give pure 1ꢀbromoꢀ 1H, pyreneꢀH), 8.89 (d, J= 8.86 Hz, 1H, pyreneꢀH), 8.90 (s, 1H,

7ꢀtertꢀbutylpyrene (2a) in 50% yield (170 mg) as white powder.

pyreneꢀH), 8.92 (s, 1H, pyreneꢀH).

Run 4: To a mixture of 2ꢀtertꢀbutylpyrene (1) (2.58 g, 10 mmol) in Run 7: Synthesis of 1,3,5,9-tetrabromo-7-tert-butylpyrene (2f)

CH₂Cl₂(30 mL) was added dropꢀwise a solution of BTMABr₃A mixture of 2ꢀtertꢀbutylpyrene (0.512 g, 2 mmol) and iron powder

(benzyltrimethylammonium tribromide) (13.7 g, 35 mmol) in (0.56 g, 10 mmol) were added to CH₂Cl₂(10 mL) at 0 °C with

CH₂Cl₂(20 mL) at 0 °C for 1 h under an argon atmosphere. The stirring for 15 min. A solution of Br₂(0.61 mL, 12 mmol) in CH₂Cl₂

resulting mixture was allowed to slowly warm up to 28 °C and (15 mmol) was slowly added dropꢀwise with vigorous stirring. After

stirred overnight. The reaction mixture was poured into iceꢀwater (60 this addition, the reaction mixture was continuously stirred for 4 h

mL) and neutralized with an aqueous 10% Na₂S₂O₃solution. The at28 °C. The mixture was quenched with Na₂S₂O₃(10%) and

solution was extracted with CH₂Cl₂(2 × 50 mL). The organic layer extracted with CH₂Cl₂(2 × 50 mL). The combined organic extracts

was washed with water (2 × 20 mL) and saturated brine (20 mL), we rewashed with water and brine and evaporated. The crude

and then the solution was dried (MgSO₄) and condensed under product was gray in color. The crude product was insoluble in

reduced pressure. The crude compound was washed with hot hexane common organic solvents such as benzene, hexane, methanol etc.

to afford pure 1,3ꢀdibromoꢀ7ꢀtertꢀbutylpyrene (2b) in 76% yield and slightly dissolved in CH₂Cl₂or CHCl₃. The residue was

(3.02 g) as a colourless solid. Recrystallization from hexane gave 2b dissolved in hot CHCl₃and filtered, and the product was crystallized

1

as a gray solid, Mp: 199.5–201.2 °C. The H NMR spectrum agreed from CHCl₃to give pure 1,3,5,9ꢀtetrabromoꢀ7ꢀtertꢀbutylpyrene (2f)

with the reported values.^{25 1}H NMR (300 MHz, CDCl₃): δ (TMS, in 84% yield (978 mg) as a white powder. Mp: 303.4–305.0 °C. IR

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(KBr): ν_max(cm^ꢀ1) = 2962, 2365, 1579, 1523, 1461, 1425, 1392, and brine. The organic extracts were dried with MgSO₄and

1

1363, 1267,1195, 1132, 1027, 1012, 941, 877, 809, 655, 474. H evaporated. The residue was purified by column chromatography

NMR (300MHz, CDCl₃): δ (TMS, ppm) 1.65 (s, 9H, tBu), 8.47 (s, eluting with CH₂Cl₂ꢀhexane (2:1) to give 3a as a white solid.

1H, pyreneꢀH2), 8.71 (s, 2H, pyreneꢀH), 8.79 (s, 2H, pyreneꢀH). Due Recrystallization from (CH₂Cl₂ꢀhexane, 1:1) gave 7ꢀtertꢀbutylꢀ1ꢀ(4ꢀ

to the poor solubility in organic solvents it was not further methoxyphenyl) pyrene (3a) in 54% yield (235 mg) as colourless

characterized by ¹³C NMR spectroscopy. FABꢀHRMS: m/z calcd. for crystals. Mp: 141.2–143.5 °C. IR (KBr): ν_max(cm^ꢀ1) = 2952, 1604,

C₂₀H₁₄Br₄573.78; found 573.62 [M⁺]. Anal. Calcd for C₂₀H₁₄Br₄: C, 1520, 1496, 1437, 1246, 1172, 1032, 878, 849, 826, 729, 681, 567,

1

41.85; H, 2.46; found: C, 42.05; H, 2.53.

526, 489. H NMR (300 MHz, CDCl₃): δ (TMS, ppm) 1.58 (s, 9H,

Run 8: Lewis acid-catalysed bromination of 1,3,6-tribromo-7- tBu), 3.93 (s, 3H, OMe), 7.10 (d, J = 8.7 Hz, 2H, ArꢀH), 7.56 (d, J =

tert- butylpyrene (2c) 8.7Hz, 2H, ArꢀH), 7.92 (d, J = 7.8 Hz, 1H, pyreneꢀH), 7.99 (d, J = 9

A mixture of 1,3,6ꢀtribromoꢀ7ꢀtertꢀbutylpyrene (2c) (200 mg, 0.4 Hz, 1H, pyreneꢀH), 8.05 (s, 2H, pyreneꢀH), 8.15 (d, J = 1.8 Hz, 1H,

mmol) and iron powder (100 mg, 1.8 mmol) were added to CH₂Cl₂pyreneꢀH), 8.18 (d, J = 2.4 Hz, 1H, pyreneꢀH), 8.22 (d, J = 1.8 Hz,

(15 mL) at 0 °C with stirring for 15 min. A solution of Br₂(0.052mL, 1H, pyreneꢀH). ¹³C NMR (100 MHz, CDCl₃): δ (TMS, ppm) 158.9,

1.01 mmol) in CH₂Cl₂(5 mL) was slowly added dropwise with 149.1, 137.2, 133.7, 131.6, 131.3, 130.8, 130.2, 128.4, 127.5, 127.4,

vigorous stirring. After this addition, the reaction mixture was 127.29, 127.26, 125.2, 124.9, 124.4, 123.2, 122.3, 122.0, 113.8, 55.4,

continuously stirred for 4 h at 28 °C. The mixture was quenched 35.2, 31.9. FABꢀHRMS: m/z calcd. for C₂₇H₂₄O 364.18; found

with Na₂S₂O₃(10%) and extracted with CH₂Cl₂(2 × 20 mL). The 364.25 [M⁺]. Anal. Calcd for C₂₇H₂₄O: C, 88.97; H, 6.64; found: C,

combined organic extracts were washed by water and brine and 88.68; H, 6.52.

evaporated. The crude product was dried and identified by ¹H NMR 7-tert-Butyl-1,3-bis(4-methoxyphenyl)pyrene (3b) was obtained as

1

spectroscopy. The yield was evaluated by HNMR at 70% for 2e, yellow prisms (CH₂Cl₂ꢀhexane, 1:1) (113 mg, 69%). Mp: 167 °C. IR

30% for 2f. The product was not further separated and used as the (KBr): ν_max(cm^ꢀ1) = 2958, 1610, 1512, 1498, 1456, 1396, 1363,

1

mixture for the Suzuki coupling reaction. The greenishꢀyellow crude 1286, 1246, 1174, 1039, 877, 835, 727, 660, 607, 580, 553, 418. H

product was insoluble in common organic solvents such as benzene, NMR (300 MHz, CDCl₃): δ (TMS, ppm) 1.58 (s, 9 H, pyreneꢀtBu),

hexane and methanol, and slightly soluble in CH₂Cl₂or CHCl₃. So 3.93 (s, 6 H, OMe), 7.10 (d, J = 8.8 Hz, 4H, ArꢀH), 7.60 (d, J = 8.6

the crude product was recrystallized from CHCl₃to afford a small Hz, 4H, ArꢀH), 7.91 (s, 1H, pyreneꢀH), 8.00 (d, J = 9.4 Hz, 2H,

1

amount of 2e for H NMR spectra analysis, H NMR (300 MHz, pyreneꢀH), 8.18 (d, J = 9.33 Hz, 2H, pyreneꢀH), 8.19 (s, 2H, pyreneꢀ

CDCl₃): δ (TMS, ppm) 1.83 (s, 9H, tBu), 8.46 (d, J = 9.5 Hz, 1H, H). ¹³C NMR (75 MHz, CDCl₃): δ (TMS, ppm) 159.0, 149.1, 136.8,

pyreneꢀH), 8.51 (s, 1H, pyreneꢀH), 8.76 (s, 1H, pyreneꢀH), 8.85 (s, 133.5, 131.7, 131.2, 129.1, 127.6,127.4, 125.4, 125.2, 123.5, 122.0,

1H, pyreneꢀH), 8.91 (d, J = 9.9 Hz, 1H, pyreneꢀH).

Run 9: Lewis acid-catalysed bromination of 2e/2f

113.8, 55.4, 35.2, 31.9. FABꢀHRMS: m/z calcd. for C₃₄H₃₀O₂

470.22; found 470.2[M⁺]. Anal. Calcd for C₃₄H₃₀O₂: C, 86.77; H,

A mixture of 2e/2f (100 mg, 0.17 mmol) and iron powder (50 mg, 6.43; found: C, 86.53; H, 6.41.

0.9 mmol) were added to CH₂Cl₂(15 mL) at 0 °C with stirring for 7-tert-Butyl-1,3,6-tris(4-methoxyphenyl)pyrene (3c) was obtained

15min. A solution of Br₂(0.025 mL, 0.49 mmol) in CH₂Cl₂(5 mL) as yellow, needleꢀlike crystals. (CH₂Cl₂ꢀhexane, 3:1) (155 mg, 67%).

1

was slowly added dropꢀwise with vigorous stirring. After this Mp: 249 °C. H NMR (300 MHz, CDCl₃): δ (TMS, ppm) 1.41 (s, 9

addition, the reaction mixture was continuously stirred for 8 h at H, pyreneꢀtBu), 3.86 (s, 3H, OMe), 3.91 (s, 6 H, OMe), 7.00 (d, J =

28 °C. The mixture was quenched with Na₂S₂O₃(10%) and extracted 8.0 Hz, 4H, ArꢀH), 7.08 (d, J = 8.4 Hz, 2H, ArꢀH), 7.24–7.36 (m, 1H,

with CH₂Cl₂(2 × 20 mL). The combined organic extracts were pyreneꢀH, 2H, ArꢀH), 7.51 (d, J = 8.4 Hz, 2H, ArꢀH), 7.58 (d, J = 8.4

washed with water and brine and evaporated. The residue (85 mg) Hz, 2H, ArꢀH), 7.89 (s, 1H, pyreneꢀH), 7.97 (d, J = 9.6 Hz, 1H,

1

was dried and identified by H NMR spectroscopy. The yield was pyreneꢀH), 8.00 (d, J = 9.6 Hz, 1H, pyreneꢀH), 8.18 (d, J = 9.2 Hz,

evaluated by ¹H NMR spectral analysis (25 % for 2e, 75 % for 2f).

2H, pyreneꢀH), 8.37 (s, 1H, pyreneꢀH). ¹³C NMR (100 MHz,

Synthesis of 4-methoxylphenyl substituted pyrene derivatives 3

CDCl₃): δ (TMS, ppm) 158.9, 158.88, 158.7, 146.3, 136.8, 136.6,

The pyrene derivatives

3 were synthesized from resultant 136.58, 134.1, 133.6, 133.4, 133.1, 132.1, 131.7, 131.6, 130.5, 129.2,

bromopyrenes with 4ꢀmethoxylphenylboronic acid by Suzukiꢀ 127.9, 127.5, 127.1, 126.0, 125.1, 124.7, 123.4, 123.4, 113.8, 113.7,

Miyaura cross coupling reaction in good yield. Although the mixture 112.8, 55.38, 55.36, 55.29, 37.2, 33.1. FABꢀHRMS: m/z calcd. For

of bromopyrenes, 2d/2f and 2e/2f could not be separated, the final C₄₁H₃₆O₃576.27; found 576.34 [M⁺]. Anal. Calcd for C₄₁H₃₆O₃: C,

products 3d, 3e and 3f were isolated by column chromatography 85.39; H, 6.29; found: C, 85.53; H, 6.21.

without complication.

Synthesis of 7-tert-butyl-1,3,5-tris(4-methoxyphenyl)pyrene (3d)

Synthesis of 7-tert-butyl-1-(4-methoxyphenyl)pyrene (3a)

A mixture of 1ꢀbromoꢀ7ꢀtertꢀbutylpyrene 2a (400 mg, 1.2 mmol), 4ꢀ

and 1,3,5,9-tetrakis(4-methoxyphenyl)pyrene (3f)

A

mixture of 2d/2f (200 mg, approx. 0.30 mmol), 4ꢀ

methoxyphenylboronic acid (303 mg, 2.0 mmol) in toluene (12 mL) methoxyphenylboronic acid (320 mg, 5.0 mmol) in toluene (12 mL)

and ethanol (4 mL) at room temperature was stirred under argon, and and ethanol (4 mL) at room temperature was stirred under argon, and

K₂CO₃(2 M, 20 mL) solution and Pd(PPh₃)₄(70 mg, 0.06 mmol) K₂CO₃(2 M, 20 mL) solution and Pd(PPh₃)₄(70 mg, 0.06 mmol)

were added. After the mixture was stirred for 30 min. at room were added. After the mixture was stirred for 30 min. at room

temperature, the mixture was heated to 90 °C for 24 h with stirring. temperature, the mixture was heated to 90 °C for 24 h with stirring.

After cooling to room temperature, the mixture was quenched with After cooling to room temperature, the mixture was quenched with

water, extracted with CH₂Cl₂(3 × 10 mL) and washed with water water, extracted with CH₂Cl₂(3 × 15 mL), washed with water and

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ARTICLE

DOI: 10.1039/C4RA12216J

brine. The organic extracts were dried with MgSO₄and evaporated. 113.77, 113.71, 112.9, 55.35, 55.29, 37.5, 33.0. FABꢀHRMS: m/z

The residue was firstly purified by column chromatography eluting calcd. for C₄₈H₄₂O₄682.84; found 682.66 [M⁺]. Anal. Calcd for

with CH₂Cl₂ꢀhexane (2:1) to give a mixture of 7ꢀtertꢀbutylꢀ1,3,5ꢀtrisꢀ C₄₈H₄₂O₄: C, 84.43; H, 6.20; found: C, 81.90; H, 6.15. The ¹H NMR

(4ꢀmethoxyphenyl)pyrene 3d and 7ꢀtertꢀbutylꢀ1,3,5,9ꢀtetrakis(4ꢀ spectrum of 3f agreed with the reported values.¹⁸

methoxyphenyl)ꢀ pyrene 3f (20 mg) as yellow prisms. The mixture 7-tert-butyl-1,3,5,9-tetrakis(4-methoxyphenyl)pyrene (3f) was

was recrystallized from toluene solution to afford a few crystals of obtained as a yellow powder. Recrystallization from CH₂Cl₂ꢀhexane

3d; the mixture was difficult to purify by HSCCC. Further detailed (3:1) gave 7ꢀtertꢀbutylꢀ1,3,5,9ꢀtetrakis(4ꢀmethoxyphenyl)pyrene (3f)

information (such ¹³C NMR spectroscopy, MS, elemental analysis) in 65% yield (154 mg) as a yellow solid.

of 3d could not be obtained. Increasing the polarity of the eluant

Crystallography for 3.

with

CH₂Cl₂

gave

only

7ꢀtertꢀbutylꢀ1,3,5,9ꢀtetrakis(4ꢀ

1

methoxyphenyl)pyrene 3f (15 mg) as a yellow solid. The H NMR

spectrum of 3f agreed with the reported values.¹⁸Mp: 407.5°C. IR

(KBr): ν_max(cm^ꢀ1) = 2954, 1610, 1510, 1461, 1442, 1367, 1288,

1246, 1174, 1107, 1036, 831, 586, 543. ¹H NMR (300 MHz,

CDCl₃): δ (TMS, ppm) 1.38 (s, 9H, tBu), 3.90 (s, 6H, OMe), 3.92 (s,

6 H, OMe), 7.05(d, J = 1.6 Hz, 4H, ArꢀH), 7.08 (d, J = 3.1 Hz, 4H,

ArꢀH), 7.57 (d, J = 8.8 Hz, 4H, ArꢀH), 7.60 (d, J = 4.4 Hz, 4H, Arꢀ

H ), 7.92 (s, 1H,pyreneꢀH), 8.12 (s, 2H, pyreneꢀH), 8.30 (s, 2H,

pyreneꢀH). ¹³C NMR (75 MHz, CDCl₃): δ (TMS, ppm) 159.0, 158.9,

148.5, 139.1, 136.7,133.9, 133.7, 131.7, 131.2, 130.8, 129.7, 127.3,

125.6, 121.2, 113.9,113.8, 55.4, 31.7. FABꢀHRMS: m/z calcd. for

C₄₈H₄₂O₄682.84; found 682.19 [M⁺]. Anal. Calcd for C₄₈H₄₂O₄: C,

84.43; H, 6.20; found: C, 84.33; H, 6.52.

Diffraction data were collected using a Rigaku RꢀAxis Rapid for 3a,

or a Saturn724 for 3b. A Bruker SMART CCD was used for 3c, a

SMART CCD for 3d, and APEX II CCD diffractometers in the

home laboratory for 3c and 3f or at the Advanced Light Source

(ALS) Station 11.3.1 for 3e.³⁹Data were corrected for absorption on

the basis of symmetry equivalent and repeated data and Lp effects.

Structural solution and full matrix leastꢀsquares refinement were

performed with the SHELXSꢀ97 and SHELXLꢀ97 or SHELXLꢀ2013

software packages, respectively.⁴⁰The structures were solved by

direct methods and refined on F2 using all data.36 H atoms were

constrained in a riding model. In 3c the methyl groups on the tBu

group at C(17) was modeled with two sets of positions with major

occupancy 63.4(12)%. Crystallographic Data (excluding structure

factors) for the structures reported here have been deposited with the

Cambridge Crystallographic Data Centre with deposition numbers,

965757 for 3a, 879771 for 3b, 965758 for 3c, 965759 for 3d,

965760 for 3e, and 917257 for 3f. Copies can be obtained free of

charge upon application to CCDC, 12 Union Road, Cambridge CB2

1EZ, UK (Fax: +44 1223/336 033; eꢀmail: deposit@ccdc.cam.ac.uk).

Synthesis

of

7-tert-butyl-1,3,5,8-tetrakis(4-methoxyphenyl)

pyrene (3e)

A mixture of 1,3,5,8ꢀtetrabromoꢀ7ꢀtertꢀbutylpyrene 2e and 1,3,5,9ꢀ

tetrabromoꢀ7ꢀtertꢀbutylpyrene 2f (200 mg, 0.35 mmol), 4ꢀ

methoxyphenylboronic acid (303 mg, 2.0 mmol) in toluene (12 mL)

and ethanol (4 mL) at room temperature was stirred under argon, and

K₂CO₃(2 M, 20 mL) solution and Pd(PPh₃)₄(70 mg, 0.06

mmol)were added. After the mixture was stirred for 30 min. at room

temperature, it was heated to 90 °C for 24 h with stirring. After

cooling to room temperature, the mixture was quenched with water,

extracted with CH₂Cl₂(3 × 15 mL), washed with water and brine.

The organic extracts were dried with MgSO₄and evaporated. The

residue was purified by column chromatography eluting with

CH₂Cl₂to give mixture of 7ꢀtertꢀbutylꢀ1,3,5,8ꢀtetrakis(4ꢀmethoxyꢀ

phenyl)pyrene 3e as a yellow powder. Mp: 240.0–241.2 °C.

Recrystallization from (CH₂Cl₂/hexane, 4:1) gave 3e in 42% yield

(100 mg) as a yellow powder. Increasing the polarity of the eluant

with CH₂Cl₂afforded 7ꢀtertꢀbutylꢀ1,3,5,9ꢀtetrakis(4ꢀmethoxyꢀ

phenyl)pyrene 3f in 17% yield (40 mg) as a yellow solid.

Acknowledgments

This work was performed under the Cooperative Research

Program of “Network Joint Research Center for Materials and

Devices (Institute for Materials Chemistry and Engineering, Kyushu

University)”. We would like to thank the OTEC at Saga University

and the International Collaborative Project Fund of Guizhou

province at Guizhou University for financial support. We also would

like to thank the EPSRC, The Royal Society of Chemistry (travel

grants to CR) and The Scientific Research Common Program of

Beijing Municipal Commission of Education for financial support.

Thanks Dr. Kai Chen (Nanjing University) for refining the Xꢀray

diffraction data for 3a, 3b and 3d. The Advanced Light Source is

supported by the Director, Office of Science, Office of Basic Energy

Sciences, of the U.S. Department of Energy under Contract No. DEꢀ

AC02ꢀ05CH11231.

7-tert-Butyl-1,3,5,8-tetrakis(4-methoxyphenyl)pyrene (3e) was

obtained as pale yellow prisms (CH₂Cl₂ꢀhexane, 3:1). Mp:

240.0−241.2 °C. IR (KBr): νmax (cm^ꢀ1) = 2954, 1607, 1507, 1462,

1

1440, 1288, 1246, 1177, 1105, 1037, 832, 808, 548, 526, 472. H

NMR (300 MHz, CDCl₃): δ (TMS, ppm) 1.30 (s, 9H, pyreneꢀtBu),

3.88 (s, 3H, OMe), 3.89 (s, 3H, OMe),3.92 (s, 6H, OMe),7.00 (m,8H,

ArꢀH), 7.29 (d, J = 8.4 Hz, 2H, ArꢀH), 7.35 (d, J = 9.5 Hz, 2H,

pyreneꢀH), 7.54 (d, J = 8.61 Hz, 2H, 2H, ArꢀH), 7.59 (d, J = 8.43 Hz,

2H, ArꢀH), 7.60 (d, J = 8.61 Hz, 2H, ArꢀH), 7.90 (s, 1H, pyreneꢀ

H),7.97 (d, J = 9.69 Hz, 1H, pyreneꢀH), 8.12 (s, 1H, pyreneꢀH), 8.51

(s, 1H, pyreneꢀH). ¹³C NMR (100 MHz, CDCl₃): δ (TMS, ppm)

159.0, 158.9, 158.7, 146.0, 138.9, 136.9, 136.6, 136.3, 134.2, 133.6,

133.5, 133.1, 132.2, 131.62, 131.59, 131.2, 129.7, 129.5, 127.7,

127.0, 126.1, 125.5, 124.6, 124.5, 123.8, 122.5, 113.9, 113.81,

Notes and references

^aBeijing Institute of Graphic Communication, , Beijing 102600 P.R. China.

b

Department of Applied Chemistry, Faculty of Science and Engineering,

Saga University, Honjoꢀmachi 1, Saga 840ꢀ8502 Japan.Eꢀmail:

yamatot@cc.sagaꢀu.ac.jp.

c

Emergent Molecular Function Research Group, RIKEN Center for

Emergent Matter Science (CEMS), Wako, Saitama 351ꢀ0198, Japan.

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DOI: 10.1039/C4RA12216J

Fox, T. Keith, M. A. AlꢀLaham, C. Y. Peng, A. Nanayakkara, M.

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Iron(III) bromide catalyzed bromination of 2-tert-butylpyrene and corresponding position-dependent aryl-functionalized pyrene derivatives

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