Comparison Study of the Site-Effect on Regioisomeric Pyridyl-Pyrene Conjugates: Synthesis, Structures, and Photophysical Properties

Qing Lu, Goutam Kumar Kole, Alexandra Friedrich, Klaus Muller-Buschbaum, Zhiqiang Liu,*

Article

Comparison Study of the Site-Eﬀect on Regioisomeric Pyridyl−

Pyrene Conjugates: Synthesis, Structures, and Photophysical

Properties

Xiaoqiang Yu,* and Todd B. Marder*

Cite This: https://dx.doi.org/10.1021/acs.joc.9b03421

Read Online

ACCESS

Metrics & More

Article Recommendations

sı Supporting Information

ABSTRACT: To investigate the “site eﬀect” of pyridyl substituents on a pyrene core, four

regioisomeric monopyridyl-pyrene (1−4) and ﬁve regioisomeric dipyridyl-pyrene (5−9)

conjugates were synthesized and characterized and their structures conﬁrmed by single-crystal

X-ray diﬀraction. The photophysical properties and related frontier orbital features of these

compounds have been studied both experimentally and theoretically and demonstrate the

dependence of the properties of the compounds on the position of substitution of the pyridyl

moieties connecting to the pyrene core. It was found that the absorption spectra of 2- and 4-

substituted pyrene derivatives display similar and weak inﬂuence on the S ← S excitations,

whereas they are quite diﬀerent from those of 1-substituted isomers. The emission spectra of 1-

and 4-substituted pyrenes are quite similar, whereas those of 2-substituted isomers display the

largest bathochromic shift. The 1,6-disubstituted compound 5 exhibits a near-unity emission

quantum yield in solution, which is nearly three times higher than those of other regioisomeric dipyridyl-pyrenes. In addition, the

tetrasubstituted 1,6-dipyridyl-3,8-di-n-butyl-pyrene (10) exhibits the highest solid-state quantum yield of 0.24 among all of the 10

pyridyl-pyrenes prepared in this study.

INTRODUCTION

hindered sites and are thus favorable for sterically controlled

■

15−17

reactions, such as Ir-catalyzed direct borylation

or tert-

Pyrene is a prototypical polycyclic aromatic hydrocarbon and

is a well-studied fundamental ﬂuorophore. The speciﬁc

properties of pyrene, such as its long-lived excited state, high

ﬂuorescence quantum yield, and propensity for excimer

formation, have attracted many scientists to develop and

extend the applications of pyrene in a wide variety of modern

butylation. The 4-, 5-, 9-, and 10-positions of pyrene, also

known as the K-region, lack either steric or electronic

advantages. The “localized” double-bond character of C4−

C5 and C9−C10 has been utilized for oxidation or

hydrogenation with moderate yields and for a Heck-type

−7

sciences.

An excimer is deﬁned as a complex of two

arylation, but there remain only limited examples of direct

21−23

identical molecules that is stable only when one of them is in

an excited state. The propensity of pyrene to form excimers

enhances intermolecular charge mobility, an important factor

for organic optoelectronic devices. Many pyrene derivatives

have been designed and prepared for use as organic

functionalization of pyrene at these sites.

Several groups have reported the dependence of opto-

electronic properties of pyrene derivatives on the site of

substituents connecting to pyrene, which could be termed as

the “site-eﬀect.” Filichev et al. reported that signiﬁcant

alterations in thermal stability and ﬂuorescence of pyrene

decorated with twisted intercalating nucleic acids were highly

10−12

semiconductors or ﬂuorescent probes.

Although pyrene itself seems simple and highly symmetrical,

its 10 peripheral reactive sites (C−H bonds) can easily be

divided into three classes depending on the symmetry and

chemical environment, each possessing diﬀerent electronic and

steric features and corresponding to diﬀerent chemical

reactivities. The 1-, 3-, 6-, and 8-positions of pyrene are the

sites of maximum contributions of the highest occupied

molecular orbital (HOMO) and hence favorable for electro-

inﬂuenced by the ethynylpyrene isomers used. Park et al.’s

work on the symmetrically bis-substituted pyrene (1,6-, 4,9-,

and 1,8-positions) demonstrated the higher organic light-

emitting diode eﬃciency of the 1,8-substituted isomer over

Received: December 19, 2019

philic aromatic substitution, such as direct bromination or

formylation. Most pyrene derivatives result from reactions at

these “common sites.” In contrast, the 2- and 7-positions of

pyrene lie on a nodal plane of both the HOMO and lowest

unoccupied molecular orbital (LUMO), but are the least

XXXX American Chemical Society

J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

Article

Scheme 1. Synthetic Route to Compounds 1−10

others. Feng et al. reported that the positions and degree of

substitution in multisubstituted pyrenes (1-, 1,3,6,8-, 1,3,7-,

and 1,3,5,7,9-positions) can tune their thermal and photo-

bromo-pyridine or, conversely, a pyridine boronate ester with a

bromo-pyrene. Because 1-bromopyrene and 1,6-dibromopyr-

ene can be easily prepared by direct electrophilic bromination

of pyrene, and they are in fact commercially available, the

syntheses of 1 and 5 are quite straight forward. Similarly,

compound 10 was synthesized via additional Li−Br exchange,

alkylation, and bromination before the ﬁnal coupling reaction.

For the 2- and 2,7-substituted pyrene derivatives 2, 3, 6, and 7,

versatile 2- or 2,7-pyrene pinacol boronates developed by

Marder et al., prepared via Ir-catalyzed C−H borylation of

6,27

physical properties.

tetraphenylethane conjugates as blue AIEgens indicated that

the 4-substituted pyrene exhibited the best performance. We

also carried out “site-eﬀect” studies on regioisomeric pyrene-

However, Li’s work on pyrene−

indoliums as far-red ﬂuorescent dyes and pyrene-fused

thienoacenes as organic semiconductors. To elucidate the

intrinsic “site-eﬀect” in depth, we fully elaborated our

experimental and theoretical studies on the photophysical

properties of 1-, 2-, and 2,7-substituted pyrene derivatives,

cyclometalated iridium complexes containing the isomeric 1-

pyrene, are the most eﬃcient precursors. However, in these

cases, a phase-transfer agent is necessary to improve the yield

of the Suzuki−Miyaura coupling of 2-(Bpin)pyrene or 2,7-

bis(Bpin)pyrene. Although we have reported the Ir-catalyzed

C−H borylation at the K-region of some 2,7-substituted

and 2-(2′-pyridyl)pyrene (3) ligand, and 4,9-substituted

pyrene derivatives. All of these studies demonstrated several

2,33

“

site-eﬀects” of pyrene derivatives.

Herein, a series of regioisomeric pyridyl−pyrene conjugates

which focused on mono-, di-, and tetrasubstitutions at the 1-,

pyrene derivatives,

the syntheses of K-region-only

substituted compounds such as 4, 8, and 9 still rely on

multistep processes. During the reduction−bromination−

dehydrogenation process, the dibrominated isomers 18 and 19

were diﬃcult to separate by column chromatography on silica

gel or recrystallization, and hence the mixture was directly used

-, and 4-positions of pyrene were designed and synthesized.

Their photophysical properties and single-crystal structures

were studied by experiment and theoretical calculations, which

provide insight into the “site-eﬀect” of pyrene. Although 4,10-

substituted pyrenes were rarely reported in the literature,

because they were diﬃcult to isolate from mixtures of 4,9- and

,10-isomers as the minor fraction, we herein successfully

isolated 4,10-bis(4′-pyridyl)pyrene, which enabled us to

provide a complete comparison study on four kinds of

symmetrically bis-substituted pyrene (1,6-, 2,7-, 4,9-, and

in the subsequent reaction. Although the H nuclear magnetic

34,35

resonance (NMR) spectrum of the crude products reveals that

it contains 8 and 9 in a ratio of 4:1 and the TLC reveals that

these two components have very close R values, the ﬁnal

products 8 and 9 were successfully separated via careful

fractional crystallization.

The melting points of the regioisomers show large

diﬀerences. For the monosubstituted compounds, the melting

points of 1- and 4-substituted 1 and 4 are quite similar, but

much lower than that of 2-substituted 2. Similarly, for the bis-

substituted compounds, the melting points of 1,6- and 4,10-

substituted 5 and 9 are quite close, but are much lower than

that of 2,7-substituted 6. The two polymorphs of 6 also show

distinctly diﬀerent melting points, with 6-α melting at 302 °C

and 6-β melting at 321 °C. All 2′-pyridyl derivatives have lower

melting points than those of 4′-pyridyl-substituted compounds,

which may be related to their nearly planar crystal packing.

,10-) compounds. The pyridyl group was chosen as the

substituent because of its versatile potential as a precursor of

cationic ﬂuorescent dyes

36−39

and as an eﬀective ligand to

develop various kinds of organometallic complexes, poly-

mers, and metal−organic frameworks (MOFs).

RESULTS AND DISCUSSION

■

Synthesis. As outlined in Scheme 1, all of these pyridyl−

pyrene conjugates were synthesized through ordinary Suzuki−

Miyaura coupling reactions of pyrene boronate esters with

The Journal of Organic Chemistry

J. Org. Chem. XXXX, XXX, XXX−XXX

Article

Figure 1. H NMR spectra of compounds 1, 2, 4, 5, 6, 8, and 9.

H NMR Spectra Analysis. All of the pyridyl−pyrene

conjugates are soluble in common solvents and were fully

characterized by high-resolution mass spectra (HRMS) and H

NMR, C NMR, and infrared (IR) spectroscopies. The H

NMR spectra of regioisomeric pyrene derivatives clearly

demonstrate a “site-eﬀect.” We ﬁrst examined the spectra of

monosubstituted compounds 1, 2, and 4. As shown in Figure

, the chemical shifts of H are all close to 8.80 ppm, and their

distance from the pyrene core results in little inﬂuence on the

shift. However, the chemical shifts of H in 1, 2, and 4 are 7.64,

.00, and 7.72 ppm, respectively, and are thus more sensitive to

the position of connection to pyrene. Stronger electron donors

at the 4-position of pyridine shift resonances of H to higher

ﬁeld, whereas stronger electron acceptors at the 4-position of

pyridine always shift resonances of H to lower ﬁeld. The

diﬀerence between the chemical shifts of H in 1, 2, and 4

suggests that the 1- and 4-positions of pyrene can be regarded

as stronger donors than the 2-position, consistent with the

aforementioned fact that carbons 2 and 7 lie on the nodal

plane of the pyrene HOMO. This point is also supported by an

analysis of the electronic static potential (ESP) of pyrene, as

shown in Figure S95 (Supporting Information). The ESP

values for the C1, C2, and C4 atoms in unsubstituted pyrene

are −0.226, −0.122, and −0.195, respectively, which also

clearly indicate the “site-eﬀect” of the electron-donating ability

of diﬀerent positions, in agreement with the NMR analysis. H

NMR resonances for the H^aand H of bis-substituted

compounds 5 (8.83, 7.63), 6 (8.79, 7.82), and 8 (8.84, 7.73)

also display a trend very similar to those of the monosub-

stituted compounds, in agreement with the ESP analysis.

Single-Crystal Structures from X-ray Diﬀraction.

Single crystals of compounds 1−10 (Figure 2) suitable for

X-ray diﬀraction were successfully grown from ethanol or

dichloromethane (DCM) or a mixture of the two solvents,

except for 6-β which was obtained from dimethylformamide

under solvothermal conditions. Crystal data and experimental

details are listed in Tables S1−S5 (Supporting Information).

The data for 3 are nearly identical with those reported

Figure 2. Molecular structures of compounds 1−10 from single-

crystal X-ray diﬀraction studies. Atomic displacement parameters are

shown with 50% probability. The numbers in red indicate the dihedral

angles between pyrene and pyridine planes.

substituted isomers shown in Figure 2. The dihedral angle of

polymorph 6-α is smaller (12.1°), whereas that of polymorph

-β is 38.6°. However, 2′-pyridyl derivatives 3 and 7 adopt

nearly coplanar conﬁgurations with dihedral angles of only 2.1

and 10.7°, respectively. These planar structures might result

from intramolecular C−H···N hydrogen bonding between the

N atom of 2′-pyridine and an adjacent C−H on pyrene (the

C···N distance is 2.85 Å in 3 and 2.78 Å in 7), which forms a

near-planar ﬁve-membered ring. The molecular structures

obtained from single-crystal X-ray diﬀraction agree well with

theoretical optimizations (vide infra).

previously, and two polymorphs of compound 6 were

identiﬁed. The molecular structures are presented in Figure 2,

with key bond lengths and angles given in Table S6

Supporting Information).

All 4′-pyridyl derivatives adopt non-coplanar conﬁgurations

Compounds 1−9 crystallize in monoclinic space groups, 1,

with large dihedral angles between the pyrene and pyridine

planes in most cases (except for 6-α), and the 1- and 4-

substituted compounds have much larger angles than the 2-

3, 4, 5, 6-α, 9 in P2 /c, 2, 6-β, and 7 in P2 /n, and 8 in C2/c.

However, 10 crystallizes in the triclinic space group P1.

Molecules of 1−4, 6-β, and 10 show face-to-face π-stacking

J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

parallel pyrene planes (Figures 3 and S1 −S4, S6, and S10 in

Article

interactions with a distance of ca. 3.55 Å between adjacent

in Figures 4−6, and the key photophysical data are

summarized in Table 1.

We have previously carried out extensive experimental and

theoretical studies of the photophysical properties of 2- and

2,7-functionalized pyrene derivatives and also explored the

diﬀerence in characteristic photophysical properties between

isomeric 1- and 2-substituted pyrene derivatives. In general,

substitution at the 2- and 2,7-positions mainly inﬂuences the S₁

←

S₀transition of pyrene, but has a very limited inﬂuence on

the S ← S excitation of pyrene; thus, these derivatives

maintain an absorption band around 334 nm in agreement

with what we observe for 2 , 3 , 6 , and 7 in the current study, as

shown in Figure S11 (Supporting Informatio n). On the other

hand, the 1-substituted derivatives display a strong inﬂuence

on both the S ← S and S ← S excitations and normally

show a broadened, strong, bathochromically shifted absorption

at 375 nm or even lower energy, also consistent with what we

observe for 1, 5, and 10 as shown in Figure 6. However,

photophysical studies of pyrenes substituted only at the 4-

position are rare compared with their 1- or 2-substituted

isomers.

Considering the monosubstituted isomers 1, 2, and 4

(

Figure 4), the absorption spectra of 2 and 4 are very similar

Figure 3. Molecular packing in the crystal structures of 1 and 5: (a)

Sandwich-herringbone packing with face-to-face π-stacked dimers and

weak C−H···N and C−H···π interactions in 1; (b) no π−π stacking

but weak C−H···N and C−H···π interactions in 5. Atom color:

carbongray, nitrogenblue, and hydrogenwhite. Only selected

hydrogen atoms are shown for clarity.

but quite diﬀerent from that of 1. The absorption spectra of 1

and 2 are entirely consistent with our earlier research on other

pyrene derivatives. The absorption spectrum of 1 shows a

broad peak at around 345 nm without any observed vibrational

progression, and the S ← S and S ← S excitations cannot

be clearly identiﬁed. However, the absorption spectrum of 2

clearly demonstrates a pyrene-like excitation, which is

characterized by a clear vibrational ﬁne structure with a

the Supporting Information). Whereas 6-β has the largest π−π

overlap area, 10 has the least. In addition to these interactions,

weak C−H···N interactions are observed in all compounds,

except 8. Whereas intramolecular C−H···N interactions are

observed in 3 and 7, other compounds exhibit intermolecular

C−H···N interactions. Oﬀset π-stacking with a small overlap is

observed in 6-α and 7, whereas there are no π···π stacking

interactions between pyrene moieties present in 5 , 8 , and 9

−

progression of 1280 cm . For 4, although it possesses a strong

peak at around 270 nm, which can be assigned to the S ← S

transition, as in 1 and 2, the main peak at 320−340 nm with

−

vibrational progression of 1230 cm looks like a broadened

and weaker version of the absorption of 2, which can be

assigned to the S ← S excitation. However, the pyrene-like S

←

^S0 ^e^x^cⁱ^t^a^tⁱ^oⁿ^w^a^sⁿ^o^t^o^b^s^e^r^v^e^d^a^r^o^uⁿ^d⁴⁰⁰ⁿ^mⁱⁿ^t^h^e

(

Figure 3 and S5, S8, and S9 in the Supporting Information ).

absorption spectrum of 4 even when higher concentrations

were employed.

In 9, π···π interactions are present between pyridine moieties

only. Compounds 1 and 2 adopt sandwich herringbone

patterns, 3, 6-α, and 7 show γ-motif patterns, and 5 shows a

The emission spectra of the monosubstituted isomers 1, 2,

and 4 (Figure 4) show very similar overall features. The

emission of 2 clearly shows a ﬁne structure (three peaks with

herringbone pattern.

Photophysical Properties. The ultraviolet−visible ab-

−

sorption and ﬂuorescence emission spectra of compounds 1−

progression of 1300 cm ), and the emission of 1 shows only

one main peak with a shoulder, whereas the emission from 4

shows two peaks with one weak shoulder. Taking only the

highest peaks into account, the emission energies are in the

order 4 > 1 > 2 .

0 in several common solvents including toluene, tetrahy-

drofuran (THF), CH Cl , dimethyl sulfoxide (DMSO),

dioxane, etc were recorded (Figures S13 −S22 ). As there is

not much diﬀerence, only the spectra in toluene are presented

Figure 4. Absorption and normalized emission spectra of compounds 1, 2, and 4 in toluene (C = 10 μM).

The Journal of Organic Chemistry

J. Org. Chem. XXXX, XXX, XXX−XXX

Figure 5. Absorption and normalized emission spectra of compounds 5 , 6 , 8 , and 9 in toluene (C = 10 μ M).

Article

Figure 6. Absorption and normalized emission spectra of compounds 1, 5, and 10 in toluene (C = 10 μM).

Table 1. Photophysical Data for Compounds 1−10

λ_e_m

(solid)

(nm)

λ_a_b_s

Compound (nm) ε (10 M cm⁻¹

(solution)

(nm)

Δv

Stokes shift (solution)

(solid)

(%)

−1

(cm⁻¹)

1026

−1

)

(cm

3263

)

(%)

τ (solution) (ns)

CIE (solid)

344

3.10

387, 403

τ₁= 25 (89%),

τ₂= 88 (11%)

460

(0.150, 0.159)

338

3.83

403, 425

1284

4772

τ₁= 27 (92%),

465

(0.159, 0.266)

τ = 80 (8%)

338

340

3.95

2.28

401, 424

379, 398

1408

1260

4679

3027

474

440, 495

(0.159, 0.265)

(0.172, 0.256)

τ₁= 42 (62%),

τ₂= 80 (38%)

358

340

342

346

344

372

3.07

2.87

2.46

3.16

3.25

3.30

399

2902

5460

5402

2724

2892

2785

457

488, 522

497

527

422, 530

465, 518

(0.147, 0.159)

(0.239, 0.402)

(0.161, 0.304)

(0.239, 0.600)

(0.201, 0.413)

(0.210, 0.420)

417,442

419, 445

382, 402

415

1356

1394

1302

Absorption and emission spectra were measured in toluene (C = 10 μM). The excitation wavelength λ = λ_m_a_x₍_a_b_s₎was used. The vibrational

progression was calculated from the diﬀerence in wavenumbers between the strong and moderate peaks in the emission spectra. Relative quantum

yields were measured in DMSO solution using 9,10-diphenylanthracene as the reference. Fluorescence lifetimes were measured under argon.

Absolute quantum yields of solids were measured using a calibrated integrating sphere. Chromaticity coordinates were calculated based on the

emission spectra of powders.

The “site-eﬀect” mentioned above is also clearly demon-

strated by comparison of the spectra of the symmetrically bis-

substituted pyridyl−pyrenes. As shown in Figure 5, the

absorption spectra of 8 or 9 are similar to that of 6 with a

clear ﬁne structure, whereas 5 shows only one broad, weak

peak with a bathochromic shift of 20 nm. The emission

spectral features of 8 or 9 are also similar to that of 6 with clear

ﬁne structures despite the spectral shift, whereas 5 shows only

one broad, weak peak. The emission energies, taking the

highest peaks into account, are in the order of 8 ≈ 9 > 5 > 6.

The “site-eﬀect” is also demonstrated by the diﬀerence

between monosubstituted and bis-substituted compounds. An

additive eﬀect on both absorption and emission is observed

relative to that of unsubstituted pyrene, whereas the spectrum

of 5 is more bathochromically shifted. When the substituent is

on the 2- or 2,7-position of pyrene shown in Figure S11

(

Supporting Information), the bathochromic shift produced by

the additive eﬀect is only observed in the emission spectra, but

hardly in the absorption spectra. In contrast, for a substituent

in the K-region as shown in Figure S12 (Supporting

Information ), the absorption spectra of 8 or 9 are clearly

bathochromically shifted relative to that of 4, but their

emission spectra are almost entirely overlapped. In addition,

the absorption and emission of 8 and 9 are also nearly the

same. The spectra indicate that the electronic coupling

between substituents at the 4- and 9-positions of pyrene is

(Figure 6). Thus, the spectrum of 1 is bathochromically shifted

J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

can be seen from Figure 7 , substitution at the 1- and 4-

Article

less eﬀective than that between substituents at the 1- and 6-

positions.

theoretically calculated by time-dependent density functional

theory (TD-DFT) on the CAM-B3LYP/6-31G(d) level. As

The “site-eﬀect” is not only found for the pyrene moiety, but

also for the pyridine moiety. Tang et al. reported that isomeric

tetraphenylethane−pyridines demonstrated diﬀerent photo-

physical properties, melting points, and acid dissociation

6,47

constants (pKa).

Among our regioisomeric pairs (e.g., 2

and 3 or 6 and 7), most of their key photophysical properties

(

Table 1) are comparable, indicating that the 2′-pyridyl or 4′-

pyridyl moieties do not remarkably aﬀect the frontier orbital-

related transitions when they are substituted at the 2-position

of pyrene.

Because of their relatively long-lived singlet states, pyrene

derivatives normally possess a long ﬂuorescence lifetime in

degassed solution, which can be eﬀectively quenched by O in

air. Thus, solutions for lifetime and quantum yields

measurements were prepared and placed in the cuvettes in

an argon-ﬁlled glovebox to prevent the possible interference of

O quenching. As shown in Figures S26−S28 (Supporting

Information), these decay curves (for 1, 2, and 4) need to be

ﬁt by a double exponential, leading to two ﬂuorescence lifetime

values of several nanoseconds. The shorter lifetime compo-

nents are always predominant (Table 1) for all three

compounds under argon, but still much longer than those in

air. However, their ﬂuorescence lifetimes are inﬂuenced by the

“site-eﬀect.” The lifetimes of compounds 1 and 2 are very

similar, whereas that of 4 is signiﬁcantly longer.

Emission properties of these pyridyl−pyrene conjugates in

the solid state, both as powders and single crystals, were also

examined. The emission peaks of compounds 1−10 in the

solid state were red-shifted to some extent, relative to those in

solution. As indicated by the CIE coordinates and emission

spectra, all of these compounds emitted high purity blue light

(λ_e_mmaxima lie in the range of 380−445 nm) in solution, but

their solid-state emission peaks are shifted to the blue-green

region (Table 1; Figures S41 and S42 in the Supporting

Information). Interestingly, the emissions from 1, 2, and 4 are

gradually red-shifted from blue to sky-blue and ﬁnally to blue-

green. In addition, the emission spectrum of 4 is greatly

broadened and displays the lowest quantum yield. This is likely

due to the tight packing mode of 4, as observed in its crystal

structure (Figure S4 in the Supporting Information).

Figure 7. Frontier molecular orbitals of compounds 1−10 as

calculated by DFT at the B3LYP/6-31G(d) level (isovalue = 0.02

a.u.).

positions of the compounds results in similar molecular

orbitals, and their HOMO − 1/HOMO are mainly localized

on the pyrene ring, whereas the LUMO/LUMO + 1 are

distributed between the pyrene and pyridine moieties. In

compounds substituted at the 2-position, the HOMO and

LUMO are mostly located on the pyrene core with the

exception of the LUMO of 7, whereas the HOMO − 1 and

LUMO + 1 are distributed over the whole molecule.

Therefore, the properties of 1- and 4-substituted compounds

are similar in all respects, but the properties of 2-substituted

compounds are quite diﬀerent.

Similarly, comparison between the monosubstituted and bis-

substituted compounds also indicates that the emission band

red shifts with increasing number of substituents. The bis-

substituted compounds can be seen as analogues of 9,10-

diphenylanthracene, which is a well-known ﬂuorescent stand-

ard with a near unity quantum yield. Comparatively, the 1-

substituted compounds possess ﬂuorescence quantum yields of

more than 0.80 in solution, which is much higher than those

for their isomers, for which the order is 2 < 4 ≪ 1 for

monosubstituted and 6 < 8 ≈ 9 ≪ 5 for bis-substituted

compounds. The lower solid-state emission quantum yields are

likely due to intermolecular π···π interactions. Consequently,

TD-DFT calculations using B3LYP and CAM-B3LYP

functionals reveal that both S ← S and S ← S transitions

are strongly inﬂuenced by the diﬀerent positions of

substitution, and the excitations with high oscillator strength

(f) are predominantly HOMO → LUMO transitions in most

cases, even though the band range and the general trends in

wavelengths in the experimental absorption spectra are closer

to the theoretical results when using the B3LYP functional

0 exhibits the highest solid-state quantum yield of all

compounds in this study because of the weakened

intermolecular interactions due to the steric hindrance of the

butyl moieties.

rather than CAM-B3LYP. In agreement with the literature,

Experimentally Determined Ionization Energies and

Theoretical Studies. In order to understand better the

inﬂuence of the site-eﬀect on all compounds, their ionization

energies and HOMO energy levels were measured exper-

imentally by ultraviolet photoelectron spectroscopy (UPS) and

the ordering of the excited states in pyrene was more correctly

predicted employing CAM-B3LYP than B3LYP. For 1- and 4-

substituted compounds, the ﬁrst excitation (S ← S ) with a

high oscillator strength mainly results from their HOMO →

LUMO transition, whereas the weak S ← S excitation is

The Journal of Organic Chemistry

J. Org. Chem. XXXX, XXX, XXX−XXX

Article

Figure 8. HOMO and LUMO energy levels for compounds 1-10, calculated by DFT on the B3LYP/6-31G(d) level.

mainly an equal mix of HOMO − 1 → LUMO and HOMO →

LUMO + 1 transitions. However, for most of the 2-substituted

compounds (except for 7), the order is reversed. Their S ← S

compounds, 2′-pyridyl or 4′-pyridyl derivatives have nearly

identical HOMO−LUMO gaps. Because of an additive eﬀect

of multisubstituents, the HOMO−LUMO gap gradually

decreases in the order 10 < 5 < 1 for the 1-, 1,6- and

1,3,6,8-substituted compounds.

excitations are very weak and mainly composed of HOMO − 1

LUMO and HOMO → LUMO + 1 transitions, whereas the

strong S ← S excitations with remarkable oscillator strengths

→

are mainly HOMO → LUMO transitions. Interestingly, the

theoretically simulated S₁← S₀excitation energies of

compounds 4 and 8 are very close to the S ← S excitation

energies of compounds 2 and 6, respectively, which are

consistent with the experimental spectra.

As shown in Figure 8, the HOMO and LUMO energy levels

of nearly all of the 4′-pyridine-substituted pyrene derivatives

are signiﬁcantly lower than those of pyrene (except for 10, for

which the HOMO energy level is comparable to that of pyrene,

but the LUMO level is much lower than that of pyrene),

whereas the HOMO and LUMO energy levels of 2′-pyridine-

substituted compounds (3 and 7) are very close to those of

pyrene. We assume that this may be related to the dihedral

angle between the pyrene and pyridine planes. Both crystal

structures and theoretically optimized structures indicate that

CONCLUSIONS

■

Two sets of monosubstituted and bis-substituted regioisomeric

pyridyl−pyrene conjugates were synthesized and fully charac-

terized, which enabled us to carry out an extensive study of

their structure−property relationship regarding photophysical

properties, especially focusing on the eﬀect of the position of

substitution on the pyrene core. Both experimental photo-

physical data and DFT and TD-DFT calculations on these

pyrene derivatives reveal the dependence of properties on the

position at which the pyridyl group is connected to the pyrene

core. Although the 1- and 2-substituted pyrene derivatives

display distinctly diﬀerent absorption and emission behaviors,

the absorption spectra of the 4-substituted compounds are

similar to those of 2-substituted compounds, but the emission

spectra of 4-substituted compounds are similar to those of 1-

substituted compounds. The 1,6-substituted compound 5 has a

near unity emission quantum yield in solution, whereas the

1,3,6,8-tetrasubstituted compound 10 shows the highest solid-

state quantum yield. These studies extend our previous work

showing that the position of substitution on a pyrene core

leads to distinctly diﬀerent behavior. Studies on the reactivity

of these compounds and their utility as linkers for metal

complexes, polymers, and MOFs are ongoing.

′-pyridyl derivatives adopt a nearly planar conformation with

a small dihedral angle (less than 18°), which may be due to the

intramolecular C−H···N hydrogen bonding between the N

atom of 2′-pyridine and an adjacent C−H of pyrene. However,

with a lack of this type of hydrogen bonding, 4′-pyridine

substituents tend to rotate (dihedral angle 37−57°), so that

their HOMO and LUMO are actually at lower energies. This

phenomenon is also consistent with phenyl-pyridine com-

pounds (see Table S9).

The HOMO and LUMO gaps 1 < 4 < 2 (shown in Table 2

and Figure 8) reveal the “site-eﬀect” among the regioisomers.

The HOMO−LUMO gaps of bis-substituted compounds are

smaller than those of monosubstituted derivatives, regardless of

the position of substitution. Among the 2-substituted

EXPERIMENTAL SECTION

General Experimental Methods for Synthesis and Chemical

Characterization. All reagents were purchased from commercial

sources and were used as received. The compounds 2-(Bpin)pyrene

■

(

11) and 2,7-bis(Bpin)pyrene (12) were synthesized according to

15,16

literature procedures.

NMR spectra were recorded in CDCl₃

using 300 or 400 MHz Bruker AVANCE spectrometers, and chemical

shifts are reported relative to tetramethylsilane. HRMS were recorded

in the electrospray ionization mode (spray voltage 3.5 kV) at 350 °C

Table 2. Energies of Frontier Orbitals of Compounds 1−10

UPS

DFT

on an Agilent 6510 Accurate Mass Q-TOF mass spectrometer. IR

spectra were recorded on a NEXUS 670 spectrometer. Melting points

were measured on an X-4 digital display micromelting point

apparatus.

General Synthesis Procedure of Suzuki−Miyaura Coupling

Reactions for Compounds 1−10. Procedure A. In a 100 mL

Schlenk ﬂask, bromopyrene (1 equiv), (4-pyridine)boronic acid

pinacol ester (1.3 equiv for monopyridyl-pyrene compounds 1 and 4;

(eV)

HOMO

(eV)

LUMO

(eV)

HOMO

(eV)

LUMO

(eV)

compound

(eV)

−5.94

−5.26

−5.02

−5.15

−5.83

−5.45

−4.90

−5.12

−5.26

−2.63

−1.69

−1.47

−1.70

−2.66

−1.90

−1.37

−1.71

−1.69

−2.24

3.31

3.57

3.55

3.45

3.17

3.55

3.53

3.41

3.43

3.02

−5.44

−5.53

−5.32

−5.47

−5.54

−5.72

−5.31

−5.59

−5.31

−1.78

−1.69

−1.47

−1.71

−2.02

−1.87

−1.48

−1.89

−1.94

3.66

3.84

3.85

3.76

3.52

3.85

3.83

3.70

3.37

.8 equiv for dipyridyl-pyrene compounds 5, 8, 9, and 10), Pd(PPh₃)₄

(2% equiv for compounds 1 and 4; 4% equiv for compounds 5, 8, 9,

and 10), tetrabutyl ammonium bromide (0.1 equiv), potassium

carbonate (1 equiv), toluene (20 mL), and H O (2 mL) were added

in sequence. The reaction mixture was heated to reﬂux in an oil bath

for 24 h under a nitrogen atmosphere. The solution was cooled to

room temperature (RT), the ﬁltrate was extracted with CH Cl

Energy level of HOMO measured by UPS. Energy gap calculated

(DCM), and the organic phase was dried over anhydrous sodium

from the onset of absorption.

sulfate for 4 h. Then, sodium sulfate was removed by ﬁltration, and

J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

Article

the solution was concentrated in vacuo. The residue was dissolved in

toluene (100 mL) and aqueous potassium carbonate was added (2.4

NMR (400 MHz, CDCl ): δ (ppm) 7.36 (s, 1H), 7.15 (d, 2H, J = 3

Hz), 3.00−3.11 (m, 8H), 2.01−2.07 (m, 4H). The H NMR

−

mol L in H O, 3 mL). Then, the mixture was reﬂuxed for 3 h. The

spectrum of 14 is in agreement with the literature.

mixture was ﬁltered while hot, and the ﬁltrate was poured into a

beaker for recrystallization.

Synthesis of 4-Bromopyrene (15). In a 250 mL round-bottom

ﬂask, compound 14 (1.0 g, 3.5 mmol) and 2,3-dicyano-5,6-

dichlorobenzoquinone (DDQ, 4.0 g, 17.6 mmol) were dissolved in

toluene (30 mL). The mixture was stirred and reﬂuxed for 12 h at 110

°C in an oil bath. The reaction was cooled to RT and ﬁltered; the

ﬁltrate was puriﬁed by column chromatography on silica gel eluting

Procedure B. In a 100 mL Schlenk ﬂask, (Bpin)pyrene (1 equiv),

-bromopyridine hydrochloride or 2-bromopyridine (1.3 equiv for

monopyridyl-pyrene compounds 2 and 3; 2.8 equiv for dipyridyl-

pyrene compounds 6 and 7), Pd(PPh ) (2% equiv for compounds 2

and 3; 4% equiv for compounds 6 and 7), tetrabutyl ammonium

bromide (0.1 mol), potassium carbonate (1 equiv), toluene (20 mL),

with petroleum ether to yield 15 as a light brown powder (0.34 g,

35%). H NMR (300 MHz, CDCl ): δ (ppm) 8.60 (d, 1H, J = 8 Hz),

and H O (2 mL) were added in sequence. The subsequent

8.44 (s, 1H), 7.98−8.26 (m, 7H). The H NMR spectrum of 15 is in

experimental procedure is the same as that for Procedure A.

Synthesis of 1-(4′-pyridyl)pyrene (1). According to the general

synthesis Procedure A for the Suzuki−Miyaura coupling reactions,

agreement with the literature.

Synthesis of 4-(4′-pyridyl)pyrene (4). According to the general

synthesis Procedure A for the Suzuki−Miyaura coupling reactions,

compound 1 was isolated as a white solid (0.24 g, 34%).

compound 4 was isolated as a light brown powder (0.15 g, 30%).

mp 138−139 °C; H NMR (300 MHz, CDCl ): δ (ppm) 8.83 (br

mp 138−140 °C; H NMR (300 MHz, CDCl ): δ (ppm) 8.84 (br

s, 2H), 8.28−8.18 (m, 3H), 8.14 (d, 2H, J = 4 Hz), 8.12 (d, 2H, J = 2

Hz), 8.06 (t, 1H, J = 8 Hz), 7.96 (d, 1H, J = 8 Hz), 7.64 (d, 2H, J = 5

s, 2H), 8.26 (d, 2H, J = 8 Hz), 8.20 (t, 1H, J = 7 Hz, J = 8 Hz), 8.14

(s, 2H), 8.10 (d, 1H, J = 5 Hz), 8.08 (d, 1H, J = 5 Hz), 8.04 (s, 1H),

Hz). ¹³C{ H} NMR (75 MHz, CDCl ): δ (ppm) 149.6, 149.4, 131.5,

7.99 (t, 1H, J = 8 Hz), 7.72 (d, 2H, J = 6 Hz). C{ H} NMR (100

31.4, 130.8, 128.4, 128.3, 128.2, 127.3, 127.0, 126.3, 125.7, 125.3,

MHz, CDCl ): δ (ppm) 149.6, 149.3, 136.6, 131.5, 131.1, 130.3,

24.9, 124.8, 124.7, 124.1. HRMS (m/z): [M + H] calcd for

129.1, 128.3, 127.7, 127.5, 127.4, 126.4, 126.0, 125.9, 125.7, 125.5,

−1

C H N, 280.1126; found, 280.1099. IR (cm ): 3040, 2162, 1949,

125.2, 124.9, 124.5, 123.1. HRMS (m/z): [M + H] calcd for

−

882, 1808, 1626, 1594, 1547, 1531, 1489, 1455, 1435, 1410, 1296,

242, 1217, 1193, 1176, 1156, 1141, 1117, 1085, 1067, 1014, 988,

66, 943, 906, 844, 832, 823, 798, 761, 720, 693, 681, 665.

Synthesis of 2-(4′-pyridyl)pyrene (2). According to the general

C H N, 280.1126; found, 280.1108. IR (cm ): 3321, 3022, 2961,

21 14

2918, 2849, 2447, 2163, 1919, 1653, 1613, 1596, 1538, 1496, 1454,

1422, 1409, 1320.5, 1285, 1260, 1218, 1171, 1097, 1067, 1017, 993,

934, 917, 895, 872, 829, 818, 771, 761, 717, 691, 673, 664.

Synthesis of 1,6-Bis(4′-pyridyl)pyrene (5). According to the

general synthesis Procedure A for the Suzuki−Miyaura coupling

reactions, compound 5 was isolated as a light yellow powder (0.86 g,

synthesis Procedure B for the Suzuki−Miyaura coupling reactions,

compound 2 was isolated as a white solid (0.55 g, 65%).

mp 193−194 °C; H NMR (400 MHz, CDCl ): δ (ppm) 8.81 (d,

H, J = 4 Hz), 8.46 (s, 2H), 8.25 (d, 2H, J = 8 Hz), 8.17 (d, 4H, J = 1

89%).

Hz), 8.08 (t, 1H, J = 8 Hz, J = 8 Hz), 8.00 (d, 2H, J = 6 Hz).

mp 263−265 °C; H NMR (300 MHz, CDCl ): δ (ppm) 8.83 (d,

C{ H} NMR (75 MHz, CDCl ): δ (ppm) 149.7, 149.4, 135.3,

4H, J = 5 Hz), 8.29 (d, 2H, J = 8 Hz), 8.20−8.11 (m, 4H), 8.01 (d,

31.8, 131.3, 128.3, 127.4, 126.5, 125.5, 124.9, 124.4, 123.2, 122.7.

2H, J = 8 Hz), 7.63 (d, 4H, J = 6 Hz). C{ H} NMR (75 MHz,

HRMS (m/z): [M + H] calcd for C H N, 280.1126; found,

CDCl

): δ (ppm) 149.6, 149.4, 134.9, 131.2, 128.4, 128.3, 127.5,

−

80.1107. IR (cm ): 3044, 2163, 1927, 1774, 1638, 1594, 1553,

541, 1498, 1469, 1440, 1414, 1375, 1327, 1303, 1240, 1224, 1178,

141, 1091, 1070, 991, 980, 971, 901, 887, 867, 841, 827, 814, 758,

12, 677, 666.

125.7, 125.2, 125.0, 124.9. HRMS (m/z): [M + H] calcd for

C H N , 357.1392; found, 357.1388. IR (cm ): 3037, 2163, 1960,

26 17 2

−

1888, 1655, 1593, 1575, 1539, 1482, 1456, 1432, 1409, 1321, 1282,

1272, 1234, 1215, 1194, 1155, 1084, 1066, 991, 955, 880, 849, 828,

817, 805, 726, 694, 681.

Synthesis of 2-(2′-pyridyl)pyrene (3). According to the general

synthesis Procedure B for the Suzuki−Miyaura coupling reactions,

compound 3 was isolated as a white solid (0.48 g, 57%).

Synthesis of 2,7-Bis(4′-pyridyl)pyrene (6). According to the

general synthesis Procedure B for the Suzuki−Miyaura coupling

reactions, compound 6 was isolated as a light yellow powder (0.64 g,

86%).

mp 132−133 °C; H NMR (400 MHz, CDCl ): δ (ppm) 8.88 (dd,

H, J = 1 Hz, J = 5 Hz), 8.86 (s, 2H), 8.22−8.18 (m, 4H), 8.15−

.11 (m, 3H), 8.03 (dd, 1H, J = 7 Hz, J = 8 Hz), 7.97 (t, 1H, J = 8

mp 300−302 °C (6-α) and 321 °C (6-β); H NMR (400 MHz,

Hz), 7.41 (dd, 1H, J = 5 Hz, J = 7 Hz). C{ H} NMR (100 MHz,

CDCl ): δ (ppm) 157.7, 149.8, 137.2, 131.6, 131.4, 127.8, 127.8,

CDCl ): δ (ppm) 8.79 (dd, 4H, J = 2 Hz, J = 4 Hz), 8.46 (s, 4H),

8.20 (s, 4H), 7.82 (dd, 4H, J = 2 Hz, J = 4 Hz). C{ H} NMR (100

1 2

26.2, 125.2, 125.0, 124.6, 123.4, 122.3, 121.5, MS (m/z): [M + H]

MHz, CDCl ): δ (ppm) 150.5, 148.6, 136.3, 131.9, 128.3, 124.5,

−

calcd for C H N, 279; found, 279. IR (cm ): 3033, 2921, 2191,

123.8, 122.5. HRMS (m/z): [M + H] calcd for C H N , 357.1392;

26 17

−

912, 1846, 1763, 1672, 1642, 1585, 1567, 1483, 1464, 1446, 1427,

415, 1372, 1317, 1273, 1240, 1212, 1197, 1173, 1149, 1113, 1088,

078, 1063, 1046, 991, 978, 957, 908, 890, 883, 872, 837, 816, 780,

51, 736, 722, 705, 669.

found, 357.1386. IR (cm ): 3027, 2163, 1924, 1759, 1630, 1589,

1550, 1504, 1480, 1446, 1417, 1381, 1335.6, 1229, 1153, 1067, 1001,

992, 964, 885, 824, 797, 734, 706, 666.

Synthesis of 2,7-Bis(2′-pyridyl)pyrene (7). According to the

general synthesis Procedure B for the Suzuki−Miyaura coupling

reactions, compound 7 was isolated as a light yellow powder (0.61 g,

Synthesis of 1,2,3,6,7,8-Hexahydropyrene (13). In a 500 mL

round-bottom ﬂask, pyrene (2.0 g, 9.9 mmol) in 1-pentanol (50 mL)

was stirred and reﬂuxed. Small pieces of sodium (2.0 g, 87 mmol)

were very slowly added over 15 min to the reaction ﬂask, and the

mixture was stirred for 2 h. After cooling to RT and ﬁltering to obtain

74%).

mp 230−232 °C; H NMR (300 MHz, CDCl ): δ (ppm) 8.85 (dd,

2H, J = 1 Hz, J = 2 Hz), 8.83 (s, 4H), 8.19 (s, 4H), 8.09 (d, 2H, J =

the ﬁltrate, the mixture was extracted with H O. The organic phase

was evaporated to dryness in vacuo, and the solid residue was

8 Hz), 7.88 (td, 2H, J = 2 Hz, J = 8 Hz), 7.36−7.31 (m, 2H).

13 1

C{ H} NMR (100 MHz, CDCl ): δ (ppm) 157.7, 150.0, 137.1,

recrystallized from ethanol to obtain compound 13 as a white powder

137.0, 131.8, 128.2, 124.9, 123.6, 122.3, 121.4. MS (m/z): [M + H]

calcd for C H N , 357.1; found, 357.1. IR (cm ): 3040, 2163,

−1

(

0.92 g, 44%). H NMR (400 MHz, CDCl ): δ (ppm) 7.13 (s, 4H),

26 17

.07 (t, 8H, J = 6 Hz), 2.02−2.08 (m, 4H). The H NMR spectra of

3 is consistent with the data reported in the literature.

1977, 1607, 1582, 1547, 1478, 1446, 1427, 1409, 1315, 1280, 1260,

1243, 1222, 1196, 1162, 1152, 1117, 1093, 1081, 1049, 1022, 993,

901, 883, 810, 772, 740, 693, 663.

Synthesis of 4,9-Dibromo-1,2,3,6,7,8-hexahydropyrene (16) and

4,10-Dibromo-1,2,3,6,7,8-hexahydropyrene (17). In a 250 mL

Synthesis of 4-Bromo-1,2,3,6,7,8-Hexahydropyrene (14). In a 250

mL round-bottom ﬂask, Br (0.5 mL) dissolved in DCM (3 mL) was

added dropwise over 30 min into a DCM solution (10 mL) of 13 (2

g, 9.5 mmol). The mixture was stirred at RT for 30 min, after which

the product was isolated via ﬁltration and recrystallized from

round-bottom ﬂask, Br (2.0 mL) dissolved in DCM (6 mL) was

added dropwise into a DCM (30 mL) solution of compound 13 (4 g,

19 mmol) over 30 min. The mixture was stirred at RT for 30 min, and

acetonitrile giving compound 14 as a white powder (2.1 g, 76%). H

J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

Article

then the crude product was isolated by ﬁltration and recrystallized

from DCM (100 mL) to obtain a light brown product. The H NMR

spectrum showed that the product was composed of 16 and 17 in the

ratio of 4:1. Their polarities were extremely similar, and hence they

were diﬃcult to separate by conventional means such as silica gel

column chromatography and recrystallization; so, the mixture was

used for subsequent syntheses.

yellow powder. The ﬁltrate was evaporated to obtain the additional

product which was washed with methanol and dried. The combined

yield of 21 was 2.19 g, 81%. H NMR (400 MHz, CDCl ): δ (ppm)

8.24 (d, 2H, J = 9 Hz), 8.10 (d, 2H, J = 8 Hz), 8.07 (d, 2H, J = 9 Hz),

7.87 (d, 2H, J = 8 Hz), 3.30 (t, 4H, J = 8 Hz), 1.85−1.81 (m 4H),

1.55−1.51 (m, 4H), 1.00 (t, 6H, J = 7 Hz). The H NMR spectrum of

21 is in agreement with the literature.

Synthesis of 4,9-Dibromopyrene (18) and 4,10-Dibromopyrene

Synthesis of 1,6-Bis(4′-pyridyl)-3,8-dibutylpyrene (10). According

to the general synthesis procedure for the Suzuki−Miyaura coupling

reactions, compound 10 was isolated as a light green powder (0.13 g,

(

19). In a 250 mL round-bottom ﬂask, the above 4:1 mixture of 16

and 17 (1,6 g, 4.4 mmol) and DDQ (8.8 g, 38.8 mmol) were

dissolved in toluene (75 mL) and then stirred and reﬂuxed in an oil

bath for 12 h, followed by cooling to RT, evaporation of the solvent,

and recrystallization from DCM (100 mL), yielding a mixture of 18

and 19 as a light brown powder in the ratio of 4:1 (0.61 g).

23%).

mp 245−247 °C; H NMR (400 MHz, CDCl ): δ (ppm) 8.83 (d,

4H, J = 4 Hz), 8.28 (d, 2H, J = 10 Hz), 8.16 (d, 2H, J = 9 Hz), 7.85

(s, 2H), 7.70 (d, 4H, J = 6 Hz), 3.37 (t, 4H, J = 8 Hz), 1.88−1.84 (m,

Synthesis of 4,9-Bis(4′-pyridyl)pyrene (8) and 4,10-Bis(4′-

4H), 1.55−1.50 (m, 4H), 1.00 (t, 6H, J = 7 Hz, J = 8 Hz). C{ H}

pyridyl)pyrene (9). The mixture of 18 and 19 in the ratio of 4:1

NMR (100 MHz, CDCl ): δ (ppm) 149.6, 149.5, 137.2, 134.3, 128.9,

(

0.15 g, 0.43 mmol), (4-pyridine)-boronic acid pinacol ester (0.38 g,

.8 mmol), potassium carbonate (0.1 g, 0.7 mmol), Pd(PPh ) (20

28.7, 126.7, 125.9, 125.7, 124.7, 123.3. HRMS (m/z): [M + H]

−

calcd for C H N , 469.2644; found, 469.2579. IR (cm ): 3022,

34 33 2

mg, 0.016 mmol), toluene (10 mL), and H O (2 mL) were added in

2949, 2929, 2866, 2442, 2163, 1946, 1655, 1613, 1591, 1537, 1510,

1492, 1464 1411, 1374, 1325, 1306, 1217, 1178, 1102, 1067, 989,

909, 887, 844, 632, 756, 726, 702, 694, 668.

sequence into a 50 mL Schlenk ﬂask. The reaction mixture was heated

to reﬂux in an oil bath under a N atmosphere. After 24 h, the mixture

was cooled to RT, ﬁltered to collect the crude solid product which

was washed with water, petroleum, and ethanol 3 times, then

dissolved in toluene (20 mL), and reﬂuxed for 5 h. The product was

collected via ﬁltration, washed with ethanol, and dried to obtain

compound 8 as a yellow-green powder (0.063 g, 53%). The solvent

from the ﬁltrate was evaporated to dryness to yield compound 9 as a

Photophysical Properties. The ultraviolet absorption spectra in

dilute solution were recorded using a Hitachi U-2910 spectropho-

tometer, and the solution and powder ﬂuorescence spectra were

recorded using a Hitachi F-2900 spectroﬂuorimeter equipped with a

450 W Xe lamp with C = 10 μM. Relative quantum yields were

measured in dilute DMSO solutions using dilute 9,10-diphenylan-

thracene solution as a reference, and the absolute quantum yields of

solids were measured using a calibrated integrating sphere on a

C13534-31 from Hamamatsu Photonics. Single-crystal confocal

ﬂuorescent images were obtained on an Olympus FV 1200 laser

confocal ﬂuorescence microscope with excitation from a 405 nm laser,

and the crystal emission spectra were obtained by means of its spectral

imaging function. Then, the crystal emission spectra were ﬁnally

recorded with a wavelength interval of 10 nm.

light yellow solid (0.010 g, 33%).

4,9-Bis(4′-pyridyl)pyrene (8). mp 317−319 °C; H NMR (400

MHz, CDCl ): δ (ppm) 8.86 (d, 4H, J = 6 Hz), 8.31 (d, 2H, J = 7

Hz), 8.20 (d, 2H, J = 8 Hz), 8.11 (s, 2H), 8.06 (t, 2H, J = 8 Hz, J =

Hz), 7.73 (d, 4H, J = 6 Hz). C{ H} NMR (100 MHz, CDCl ): δ

(

ppm) 145.0, 132.0, 126.0, 124.5, 123.8, 121.8, 121.5, 120.4, 120.1,

19.1. HRMS (m/z): [M + H] calcd for C H N , 357.1392; found,

26 17 2

−

57.1377. IR (cm ): 3066, 3028, 2918, 2850, 2163, 1966, 1842,

649, 1593, 1542, 1505, 1464, 1444, 1433, 1409, 1394, 1318, 1305,

260, 1211, 1158, 1098, 1069, 986, 913, 898, 831, 825, 802, 160, 737,

Single-Crystal X-ray Diﬀraction. Suitable single crystals for X-

ray diﬀraction were grown by slow evaporation from ethanol or DCM

or a mixture of these solvents. The crystals were selected, coated in

perﬂuoropolyether oil, and mounted on MiTeGen sample holders.

Diﬀraction data were collected on Bruker Smart Apex II, Bruker X8

Apex II, and D8 VENTURE 4-circle diﬀractometers using graphite

monochromated Mo Kα (λ = 0.71073 Å) or Cu Kα (λ = 1.54178 Å)

radiation with CCD area detectors at diﬀerent temperatures. The

crystals were cooled using an Oxford Cryostream low-temperature

26, 696, 654.

,10-Bis(4′-pyridyl)pyrene (9). mp 247−249 °C; H NMR (400

MHz, CDCl ): δ (ppm) 8.84 (d, 4H, J = 5 Hz), 8.28 (d, 2H, J = 7

Hz), 8.19 (d, 2H, J = 8 Hz), 8.11 (t, 1H, J = 8 Hz, J = 8 Hz), 8.07 (s,

H), 7.95 (t, 1H, J = 8 Hz, J = 8 Hz), 7.64−7.62 (m, 4H). C{ H}

NMR (100 MHz, CDCl ): δ (ppm) 150.1, 148.7, 137.1, 130.1, 129.7,

28.2, 126.8, 126.2, 126.1, 125.3, 125.1, 124.2, 123.8. HRMS (m/z):

−1

[

M + H] calcd for C H N , 357.1392; found, 357.1385. IR (cm ):

device. These structures were solved by SHELXS-97 or SHELXT

021, 2922, 2851, 2163, 1936, 1719, 1592, 1541, 1492, 1453, 1433,

408, 1369, 1319, 1261, 1212, 1190, 1103, 1067, 993, 927, 911, 891,

77, 842, 828, 810, 794, 749, 724, 696, 681, 667.

and the Fourier expansion technique. All non-hydrogen atoms were

reﬁned in anisotropic approximation, with hydrogen atoms “riding” in

idealized positions, by full-matrix least-squares against F of all data,

Synthesis of 1,6-Dibutylpyrene (20). In a 250 mL round-bottom

using SHELXL2 software and the SHELXLE graphical user

ﬂask, n-butyllithium in hexane (30 mL, 48 mmol) was added dropwise

to a solution of 1,6-dibromopyrene (3.6 g, 10 mmol) dissolved in

THF (20 mL) under a N atmosphere at 0 °C. After 3.5 h of stirring

at 0 °C, 1-iodobutane (8 mL, 70 mmol) was added dropwise to the

mixture. The reaction was allowed to warm slowly to RT and stirred

overnight. The reaction was quenched with water, extracted with

DCM, and dried over anhydrous Na SO for 2 h. Then, sodium

sulfate was removed by ﬁltration, and the solution was concentrated in

vacuo. The product was puriﬁed by column chromatography on silica

gel eluting with hexane to obtain compound 20 as a yellow powder

interface. Although several crystal growth experiments were

performed on 4, 8, and 10, only small single crystals of decreased

quality were obtained from these compounds. Therefore, diﬀraction

data and reﬁnement results presented are the best that we obtained

after several attempts. However, for other compounds (1, 2, 3, 5, 6-α,

6-β, and 9), high-quality data were collected. Nevertheless, the quality

of the crystal structures of 4, 8, and 10 is suﬃcient for our discussion

of the dihedral angles and intermolecular stacking distances.

Complete structural data have been deposited with the Cambridge

Crystallographic Data Centre, and their CCDC numbers are 1956933

(1), 1956934 (2, 296 K), 1958769 (2, 100 K), 1956937 (3), 1956940

(4), 1956941 (5), 1956938 (6, 120 K, α-form), 1958770 (6, 100 K,

α-form), 1958771 (6, 100 K, β-form), 1956936 (7), 1956939 (8),

1972099 (9, 173 K), 1972098 (9, 293 K), 1956935 (10).

(

1.82 g, 58%). H NMR (400 MHz, CDCl ): δ (ppm) 8.25 (d, 2H, J

9 Hz), 8.12 (d, 2H, J = 8 Hz), 8.08 (d, 2H, J = 9 Hz), 7.88 (d, 2H, J

8 Hz), 3.35 (t, 2H, J = 8 Hz), 1.87−1.83 (m, 4H), 1.54−1.49 (m,

H), 1.02 (t, 6H, J = 7 Hz, J = 8 Hz). The H NMR spectrum of 20

is in agreement with the literature.

UPS Measurements. The UPS measurements were recorded on a

Thermo Fischer ESCALAB 250Xi instrument.

Synthesis of 1,6-Dibromo-3,8-dibutylpyrene (21). In a 250 mL

round-bottom ﬂask, Br (1.8 g, 5.7 mmol) dissolved in DCM (40 mL)

Theoretical Computations. DFT and TD-DFT calculations

was added dropwise into a DCM (10 mL) solution of 20 (1.8 g, 5.7

mmol) over 30 min. The mixture solution was stirred at RT for 30

min, and the product was collected via ﬁltration. The product was

washed with methanol and dried to yield compound 21 as a light

were performed with the Gaussian 09 program package. All

geometry optimizations were carried out using the B3LYP functional

and 6/31G(d) basis set. Frequency calculations were carried out after

geometry optimizations and only positive frequencies were obtained.

J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

4) Mateo-Alonso, A. Pyrene-fused pyrazaacenes: from small

Article

(

3) Lu, F.; Nakanishi, T. Solvent-Free Luminous Molecular Liquids.

Adv. Opt. Mater. 2019, 7, 1900176.

molecules to nanoribbons. Chem. Soc. Rev. 2014, 43, 6311−6324.

5) Nakamura, M.; Ota, F.; Takada, T.; Akagi, K.; Yamana, K.

ASSOCIATED CONTENT

sı Supporting Information

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.joc.9b03421.

■

Circularly polarized luminescence of helically assembled pyrene π −

X-ray single-crystal data of compound 1, 2 (100 K, 296

K), 3, 4, 5, 6 (120 K, α-form; 100 K, α-form; 100 K, β-

form), 7, 8, 9 (293 K, 173 K) and 10 (CIF)

NMR and HRMS spectra, X-ray crystallographic data

and crystal packing diagrams, absorption and emission

spectra in solution and solid state, ﬂuorescent images of

single crystals, CIE coordinates, IR spectra, and

computational details for compounds 1−10 (PDF)

stacks on RNA and DNA duplexes. Chirality 2018 , 30 , 602 −608.

(6) Duhamel, J. New Insights in the Study of Pyrene Excimer

Fluorescence to Characterize Macromolecules and their Supra-

molecular Assemblies in Solution. Langmuir 2012 , 28 , 6527 −6538.

(7) Jin, P.; Song, T.; Xiao, J.; Zhang, Q. Recent Progress in Using

Pyrene-4,5-diketones and Pyrene-4,5,9,10-tetraketones as Building

Blocks to Construct Large Acenes and Heteroacenes. Asian J. Org.

Chem. 2018, 7, 2130−2146.

(8) Gong, Y.; Zhan, X.; Li, Q.; Li, Z. Progress of pyrene-based

AUTHOR INFORMATION

Corresponding Authors

Zhiqiang Liu − State Key Laboratory of Crystal Materials,

Shandong University, Jinan 250100, China; orcid.org/

organic semiconductor in organic field effect transistors. Sci. China:

Chem. 2016, 59, 1623−1631.

■

(9) Ju, H.; Wang, K.; Zhang, J.; Geng, H.; Liu, Z.; Zhang, G.; Zhao,

Y.; Zhang, D. 1,6- and 2,7-trans-β -Styryl Substituted Pyrenes

Exhibiting Both missive and Semiconducting Properties in the Solid

State. Chem. Mater. 2017, 29, 3580−3588.

000-0001-7863-1759 ; Email: zqliu@sdu.edu.cn

Xiaoqiang Yu − State Key Laboratory of Crystal Materials,

Shandong University, Jinan 250100, China; orcid.org/

(10) Østergaard, M. E.; Hrdlicka, P. J. Pyrene-functionalized

oligonucleotides and locked nucleic acids (LNAs): Tools for

fundamental research, diagnostics, and nanotechnology. Chem. Soc.

Rev. 2011, 40, 5771−5788.

000-0002-4313-6464 ; Email: yuxq@sdu.edu.cn

Todd B. Marder − Institut fur Anorganische Chemie, Julius-

Maximilians-Universitat Wurzburg, 97074 Wurzburg,

(11) Wu, C.; Wang, C.; Yan, L.; Yang, C. J. Pyrene Excimer Nucleic

Germany; orcid.org/0000-0002-9990-0169;

Acid Probes for Biomolecule Signaling. J. Biomed. Nanotechnol. 2009,

5, 495−504.

Email: todd.marder@uni-wuerzburg.de

(12) Pirouz, S.; Duhamel, J. New Approaches to Characterize

Authors

Polymeric Oil Additives in Solution Based on Pyrene Excimer

Qing Lu − State Key Laboratory of Crystal Materials, Shandong

University, Jinan 250100, China

Fluorescence. J. Polym. Sci., Part B: Polym. Phys. 2017, 55 , 7 −18.

(14) Feng, X.; Hu, J.-Y.; Redshaw, C.; Yamato, T. Functionalization

13) Vollmann, H.; Becker, H.; Corell, M.; Streeck, H. Beitrage zur

Goutam Kumar Kole − Institut fu

Julius-Maximilians-Universitat Wurzburg, 97074 Wu

Germany

Alexandra Friedrich − Institut fu

Maximilians-Universitat Wurzburg, 97074 Wu

Germany

Klaus Muller-Buschbaum − Institut fu

Analytische Chemie, Justus-Liebig-Universitat

r Anorganische Chemie,

Kenntnis des Pyrens und seiner Derivate. Eur. J. Org. Chem. 1937, 1−

159.

rzburg,

of Pyrene To Prepare Luminescent Materials-Typical Examples of

Synthetic Methodology. Chem.Eur. J. 2016, 22, 11898−11916.

r Anorganische Chemie, Julius-

rzburg,

(15) Coventry, D. N.; Batsanov, A. S.; Goeta, A. E.; Howard, J. A.

K.; Marder, T. B.; Perutz, R. N. Selective Ir-catalysed borylation of

polycyclic aromatic hydrocarbons: structures of naphthalene-2,6-

bis(boronate), pyrene-2,7-bis(boronate) and perylene-2,5,8,11-tetra-

r Anorganische und

Gießen, 35392

Gießen, Germany

Complete contact information is available at:

boronate) esters. Chem. Commun. 2005, 2172−2174.

https://pubs.acs.org/10.1021/acs.joc.9b03421

(

16) Crawford, A. G.; Liu, Z.; Mkhalid, I. A. I.; Thibault, M. H.;

Schwarz, N.; Alcaraz, G.; Steffen, A.; Collings, J. C.; Batsanov, A. S.;

Howard, J. A. K.; Marder, T. B. Synthesis of 2 and 2,7-Functionalized

Pyrene Derivatives: An Application of Selective C-H Borylation.

Chem.Eur. J. 2012, 18, 5022−5035.

17) Ji, L.; Edkins, R. M.; Lorbach, A.; Krummenacher, I.; Bruckner,

Notes

The authors declare no competing ﬁnancial interest.

(

ACKNOWLEDGMENTS

C.; Eichhorn, A.; Braunschweig, H.; Engels, B.; Low, P. J.; Marder, T.

■

B. Electron Delocalization in Reduced Forms of 2-(BMes )pyrene and

This work was supported by the National Natural Science

Foundation of China (21672130 and 51773111), the Natural

Science Foundation of Shandong Province, China

(

,7-Bis(BMes )pyrene. J. Am. Chem. Soc. 2015, 137, 6750−6753.

18) Berg, A.; Jakobsen, H. J.; Johansen, S. R.; Smidsrød, O.;

Lindberg, A. A.; Jansen, G.; Lamm, B.; Samuelsson, B. Orientation in

Polyalkylation of Polycyclic Aromatic Hydrocarbons. Structure

Determination by NMR Spectroscopy. Acta Chem. Scand. 1969, 23,

(

ZR2017ZC0227), the Fundamental Research Funds of

Shandong University (2017JC011), and the Julius-Max-

imilians-Universitat Wurzburg. G.K.K. thanks the Alexander

(

67−575.

von Humboldt Foundation for a postdoctoral fellowship. We

thank engineers Jue Ding and Xin-hao Ma from Hamamatsu

Technology Company for measuring the solid-state quantum

yields.

19) Batsanov, A. S.; Collings, J. C.; Fairlamb, I. J. S.; Holland, J. P.;

Howard, J. A. K.; Lin, Z.; Marder, T. B.; Parsons, A. C.; Ward, R. M.;

Zhu, J. Requirement for an Oxidant in Pd/Cu Co-Catalyzed Terminal

Alkyne Homocoupling To Give Symmetrical 1,4-Disubstituted 1,3-

Diynes. J. Org. Chem. 2005, 70, 703−706.

REFERENCES

(20) Collins, K. D.; Honeker, R.; Vasquez-Cespedes, S.; Tang, D.-T.

́ ́

■

D.; Glorius, F. C −H arylation of triphenylene, naphthalene and

related arenes using Pd/C. Chem. Sci. 2015, 6, 1816−1824.

(21) Mochida, K.; Kawasumi, K.; Segawa, Y.; Itami, K. Direct

Arylation of Polycyclic Aromatic Hydrocarbons through Palladium

Catalysis. J. Am. Chem. Soc. 2011, 133, 10716−10719.

1) Figueira-Duarte, T. M.; Mu

Organic Electronics. Chem. Rev. 2011, 111, 7260−7314.

llen, K. Pyrene-Based Materials for

2) Islam, M. M.; Hu, Z.; Wang, Q.; Redshaw, C.; Feng, X. Pyrene-

Based Aggregation-Induced Emission Luminogens and Their

Applications. Mater. Chem. Front. 2019, 3, 762−781.

J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

(40) Biradha, K.; Fujita, M. Co-ordination polymers containing

Article

(

22) Liu, Z.; Wang, Y.; Chen, Y.; Liu, J.; Fang, Q.; Kleeberg, C.;

square grids of dimension 15 × 15 Å. J. Chem. Soc., Dalton Trans.

2000, 3805−3810.

Marder, T. B. Ir-Catalyzed Direct Borylation at the 4-Position of

Pyrene. J. Org. Chem. 2012, 77, 7124 −7128.

23) Eliseeva, M. N.; Scott, L. T. Pushing the Ir-Catalyzed C −H

(41) Marin, G.; Andruh, M.; Madalan, A. M.; Blake, A. J.; Wilson,

Polyborylation of Aromatic Compounds to Maximum Capacity by

C.; Champness, N. R.; Schroder, M. Structural Diversity in Metal −

Organic Frameworks Derived from Binuclear Alkoxo-Bridged Copper

Exploiting Reversibility. J. Am. Chem. Soc. 2012, 134, 1569−15172.

(

24) Filichev, V. V.; Astakhova, I. V.; Malakhov, A. D.; Korshun, V.

(II) Nodes and Pyridyl Linkers. Cryst. Growth Des. 2008 , 8 , 964 −975.

42) Oh, S.; Morales-Collazo, O.; Brennecke, J. F. Cation −Anion

A.; Pedersen, E. B. 1-, 2-, and 4-Ethynylpyrenes in the Structure of

Twisted Intercalating Nucleic Acids: Structure, Thermal Stability, and

Fluorescence Relationship. Chem.Eur. J. 2008, 14, 9968−9980.

Interactions in 1-Ethyl-3-methylimidazolium-Based Ionic Liquids with

Aprotic Heterocyclic Anions (AHAs). J. Phys. Chem. B 2019, 123,

274−8284.

25) Jung, M.; Lee, J.; Jung, H.; Kang, S.; Wakamiya, A.; Park, J.

43) Miure, Y.; Yamano, E.; Tanaka, A. Generation, Isolation, and

Highly efficient pyrene blue emitters for OLEDs based on substitution

Characterization of N-(Arylthio)-7-tert-butyl- and N-(Arylthio)-2,7-

di-tert-butyl-l-pyrenylaminyl Radicals. J. Org. Chem. 1994, 59, 3294−

position effect. Dyes Pigm. 2018, 158, 42−49.

(

26) Feng, X.; Hu, J.-Y.; Tomiyasu, H.; Tao, Z.; Redshaw, C.;

300.

Elsegood, M. R. J.; Horsburgh, L.; Teat, S. J.; Wei, X.-F.; Yamato, T.

Iron(III) bromide catalyzed bromination of 2-tertbutylpyrene and

corresponding positiondependent aryl-functionalized pyrene deriva-

tives. RSC Adv. 2015, 5, 8835−8848.

membered aromatic rings in crystals. J. Mol. Struct. 1999 , 474 , 81 −89.

44) Gowka, M. L.; Martynowski, D.; Kozłowska, K. Stacking of six-

45) Desiraju, G. R.; Gavezzotti, A. Crystal Structures of Polynuelear

Aromatic Hydrocarbons. Classification, Rationalization and Predic-

tion from Molecular Structure. Acta Crystallogr., Sect. B: Struct. Sci.

27) Feng, X.; Hu, J.-Y.; Wei, X.-F.; Redshaw, C.; Yamato, T.

Influence of substituent position on thermal properties, photo-

luminescence and morphology of pyrene −fluorene derivatives. J. Mol.

Struct. 2015, 1086, 216−222.

(

989, 45, 473−482.

46) Chen, X.; Shen, X. Y.; Guan, E.; Liu, Y.; Qin, A.; Sun, J. Z.;

Tang, B. Z. A pyridinyl functionalized tetraphenylethylene fluorogen

for specific sensing of trivalent cations. Chem. Commun. 2013, 49,

28) Yang, J.; Guo, Q.; Wen, X.; Gao, X.; Peng, Q.; Li, Q.; Ma, D.;

Li, Z. Pyrene-based blue AIEgens: tunable intramolecular conjugation,

good hole mobility and reversible mechanochromism. J. Mater. Chem.

C 2016, 4, 8506−8513.

(

503−1505.

47) Feng, X.; Li, Y.; He, X.; Liu, H.; Zhao, Z.; Kwok, R. T. K.;

Elsegood, M. R. J.; Lam, J. W. Y.; Tang, B. Z. A Substitution-

29) Ding, Z.; Tian, M.; Guo, L.; Liu, Z.-Q.; Yu, X. Modulate the

Dependent Light-Up Fluorescence Probe for Selectively Detecting

structure and photophysical properties of pyrene-based far-red

fluorescent cationic dyes by regio-effect. Sens. Actuators, B 2018,

Fe Ions and Its Cell Imaging Application. Adv. Funct. Mater. 2018,

48) Nandi, A.; Manna, B.; Ghosh, R. Interplay of exciton −excimer

8, 1802833.

(

76, 331−339.

30) Zhang, S.; Qiao, X.; Chen, Y.; Wang, Y.; Edkins, R. M.; Liu, Z.;

dynamics in 9,10-diphenylanthracene nanoaggregates and thin films

revealed by time-resolved spectroscopic studies. Phys. Chem. Chem.

Phys. 2019, 21, 11193−11202.

Li, H.; Fang, Q. Synthesis, Structure, and Opto-electronic Properties

of Regioisomeric Pyrene −Thienoacenes. Org. Lett. 2014, 16, 342−

45.

Pålsson, L.-O.; Tozer, D. J.; Marder, T. B. Experimental and

49) Streitwieser, A.; Lawler, R. G.; Schwaab, D.; Schwaab, D. On

(

31) Crawford, A. G.; Dwyer, A. D.; Liu, Z.; Steffen, A.; Beeby, A.;

the Bromopyrenes. J. Org. Chem. 1965 , 30 , 1470 −1473.

Theoretical Studies of the Photophysical Properties of 2- and 2,7-

Functionalized Pyrene Derivatives. J. Am. Chem. Soc. 2011, 133,

(50) Konieczny, M.; Harvey, R. G. Synthesis of Cyclopenta [cd]

pyrene. J. Org. Chem. 1979, 44, 2158−2160.

(51) Niko, Y.; Kawauchi, S.; Otsu, S.; Tokumaru, K.; Konishi, G.-i.

Fluorescence Enhancement of Pyrene Chromophores Induced by

Alkyl Groups through σ −π Conjugation: Systematic Synthesis of

Primary, Secondary, and Tertiary Alkylated Pyrenes at the 1, 3, 6, and

8 Positions and Their Photophysical Properties. J. Org. Chem. 2013,

78, 3196−3207.

(

3349−13362.

32) Edkins, R. M.; Fucke, K.; Peach, M. J. G.; Crawford, A. G.;

Marder, T. B.; Beeby, A. Syntheses, Structures, and Comparison of

the Photophysical Properties of Cyclometalated Iridium Complexes

Containing the Isomeric 1- and 2-(2 ′-pyridyl) pyrene Ligands. Inorg.

Chem. 2013, 52, 9842−9860.

(52) Sheldrick, G. M. SHELXT - integrated space-group and crystal-

structure determination. Acta Crystallogr., Sect. A: Found. Crystallogr.

2015, 71, 3−8.

(53) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr.,

Sect. A: Found. Crystallogr. 2008, 64, 112−122.

(

33) Ji, L.; Krummenacher, I.; Friedrich, A.; Lorbach, A.; Haehnel,

M.; Edkins, K.; Braunschweig, H.; Marder, T. B. Synthesis,

Photophysical, and Electrochemical Properties of Pyrenes Substituted

with Donors or Acceptors at the 4- or 4, 9-Positions. J. Org. Chem.

54) Hubschle, C. B.; Sheldrick, G. M.; Dittrich, B. ShelXle: a QT

34) Ji, L.; Fucke, K.; Bose, S. K.; Marder, T. B. Iridium-Catalyzed

018, 83, 3599−3606.

graphical user interface for SHELXL. J. Appl. Crystallogr. 2011, 44,

281−1284.

55) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;

(

Borylation of Pyrene: Irreversibility and the Influence of Ligand on

Selectivity. J. Org. Chem. 2015, 80, 661−665.

features at 3.2-3.5 μ m of polycyclic aromatic hydrocarbons with

aliphatic sidegroups. Astrophys. J. 2016 , 825 , 22.

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

B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.

P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;

Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;

Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;

Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;

Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith, T.;

Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J.

C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.;

Klene, M. J.; Knox, E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo,

J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi,

R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.;

Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;

Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.;

Cioslowski, J.; Fox, D. J. Gaussian 09, Revision B.01: Gaussian, Inc.:

Wallingford CT, 2010.

35) Yang, X. J.; Li, A.; Glaser, R.; Zhong, J. X. The C-H stretching

(

36) Loew, L. M. Design and Use of Organic Voltage Sensitive Dyes.

Adv. Exp. Med. Biol. 2015, 859, 27−53.

37) Niko, Y.; Moritomo, H.; Sugihara, H.; Suzuki, Y.; Kawamata, J.;

(

Konishi, G.-i. A novel pyrene-based two-photon active fluorescent dye

efficiently excited and emitting in the ‘tissue optical window (650 −

38) Abeywickrama, C. S.; Wijesinghe, K. J.; Stahelin, R. V.; Pang, Y.

100 nm). J. Mater. Chem. B 2015, 3, 184−190.

Bright red-emitting pyrene derivatives with a large Stokes shift for

nucleus staining. Chem. Commun. 2017, 53, 5886−5889.

(

Y.; Yu, X.; Tang, B. Z. Reaction-free and MMP-independent

fluorescent probes for long-term mitochondria visualization and

tracking. Chem. Sci. 2019, 10, 1994−2000.

39) Zhang, R.; Niu, G.; Li, X.; Guo, L.; Zhang, H.; Yang, R.; Chen,