Syntheses and UV-visible spectroscopic properties of new 'fluorophilic' fluorine-and perfluoroalkyl-substituted solvatochromic pyridinium N-phenolate betaine dyes

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY

J. Phys. Org. Chem. 2001; 14: 737–751

DOI:10.1002/poc.427

Syntheses and UV±visible spectroscopic properties of new

`¯uorophilic' ¯uorine- and per¯uoroalkyl-substituted

solvatochromic pyridinium N-phenolate betaine dyes^†‡

Christian Reichardt,* Michael Eschner^§and Gerhard SchaÈfer

Department of Chemistry and Scienti®c Center of Material Sciences, Philipps University, Hans-Meerwein-Strasse, D-35032Marburg,

Germany

Received 19 March 2001; revised 7 May 2001; accepted 24 May 2001

ABSTRACT: Syntheses and negative solvatochromism of three new ‘ﬂuorophilic’ ﬂuorine- and perﬂuoroalkyl-

substituted pyridinium N-phenolate betaine dyes 3–5 are described in order to obtain new zwitterionic dyes which

should be less basic and better soluble in perﬂuorinated solvents than the solvatochromic standard betaine dyes 1 and

2, used to establish an empirical scale of solvent polarity, called the E_T(30) or E_T^Nscale. The new betaine dyes 3–5

were designed to allow an extension of the existing E_T(30) scale to new solvents. Copyright  2001 John Wiley &

Sons, Ltd.

KEYWORDS: betaine dyes; E_T(30) values; solvatochromism; solvent effects; UV–visible spectroscopy

INTRODUCTION

temperature (25°C) and normal pressure (1 bar), accord-

ing to the equation

Solutions of the pyridinium N-phenolate betaine dye 1

(Scheme 1) are solvatochromic, thermochromic, piezo-

chromic and halochromic.^3,4That is, the longest wave-

length intramolecular charge-transfer (CT) absorption

band in the UV–visible (Vis) spectrum of dye 1 depends

on solvent polarity,^3–5solution temperature,⁶external

pressure⁷(see also Ref. 14) and the nature and

concentration of added salts⁸(for a review on chromo-

genic reagents, see Ref. 8k). Solutions of a chirally

modiﬁed betaine dye 1 with four stereogenic centers

show even the phenomenon of chiro-solvatochromism.⁹

The unusual large negative solvatochromism of the

standard betaine dye 1 was used by us to establish a

UV–Vis spectroscopically derived empirical scale of

solvent polarity, called the E_T(30) scale^3,4(for deﬁnitions

of the term ‘solvent polarity,’ see Ref. 5). E_T(30) values

are simply deﬁned as the molar transition energies

(in kcal mol^À1; 1 kcal = 4.184 kJ) of the standard betaine

dye 1, measured in solvents of different polarity at room

E_Tꢀ30ꢀkcal mol^À1 hcꢀe_maxN_A

ꢀ2:8591 Â 10^À3ꢀe_maxꢀcm^À1

28591=l_maxꢀnm

ꢀ1

*Correspondence to: C. Reichardt, Department of Chemistry and

Scientiﬁc Center of Material Sciences, Philipps University, Hans-

Meerwein-Strasse, D-35032 Marburg, Germany.

E-mail: reichard@ps1515.chemie.uni-marburg.de

^†Part XXVI in the series ‘Pyridinium N-phenoxide betaine dyes and

their application to the determination of solvent polarities.’ For Part

XXV, see Ref. 1.

^‡Dedicated to Dr John Shorter in recognition of his outstanding

contributions in the areas of physical organic chemistry and correlation

analysis in chemistry, on the occasion of his 75th birthday.

^§Based on the PhD Thesis of M. Eschner.²

Contract/grant sponsor: Deutsche Forschungsgemeinschaft.

Contract/grant sponsor: Fonds der Chemischen Industrie.

Scheme 1. Molecular structure of the betaine dyes 1±5

J. Phys. Org. Chem. 2001; 14: 737–751

Copyright  2001 John Wiley & Sons, Ltd.

¨

C. REICHARDT, M. ESCHNER AND G. SCHAFER

738

where ꢀe_maxis the wavenumber and l_maxthe wavelength

of the maximum of the long-wavelength solvatochromic

CT absorption band of betaine dye 1, and h, c, and N_Aare

Planck’s constant, the speed of light, and Avogadro’s

constant, respectively. High solvent polarity, here deﬁned

as the overall solvation capability of a solvent,⁵

corresponds to high E_T(30) values. As in the ﬁrst

publication^3athe betaine dye 1 had accidentally the

formula number 30, the number 30 was added later in

order to avoid confusion with E_T, used as abbreviation for

triplet excitation energy in photochemistry. The E_T(30)

solvent polarity scale ranges from 63.1 kcal mol^À1for

water, the most polar solvent, to 30.7 kcal mol^À1for

tetramethylsilane (TMS), as least polar solvent for

which an E_T(30) value could be experimentally

determined. In order to avoid the non-SI unit

kcal mol^À1, in 1983 the dimensionless normalized E_T^N

scale was introduced, using water (E_T^N= 1.000) and

TMS (E_T^N= 0.000) as extreme polar and non-polar

reference solvents, respectively, to ﬁx the scale accord-

ing to the equation^3b

the calculation of E_T(30) values [= E_T(1) values] for

such non-polar solvents in which the primary probe dye 1

is not soluble enough for UV–Vis spectroscopic measure-

ments. By means of correlation Eqn. (3),¹³it was possible

to extend the E_T(30) scale to non-polar solvents such as

aliphatic hydrocarbons¹³and supercritical-ﬂuid carbon

dioxide:¹⁴

E_Tꢀ2ꢀkcal mol^À1 0:9424E_Tꢀ30ꢀkcal mol^À1

1:808ꢀn 57; r 0:999; 0:17 kcal mol^À1 ꢀ3

However, even the lipophilic penta-tert-butyl-substi-

tuted betaine dye 2^3band also a hepta-tert-butyl-

substituted and a tris-tert-butyl-bis(adamantan-1-yl)-

substituted pyridinium N-phenolate betaine dye¹⁵were

not soluble in perﬂuorohydrocarbons such as perﬂuoro-

octane, perﬂuoro(methylcyclohexane) and perﬂuorode-

calin. For perﬂuorohydrocarbons, which should be less

polar than the corresponding hydrocarbons, E_T(30)

values are still lacking. This is unfortunate because

perﬂuorinated solvents have recently gained in impor-

tance as reaction media for organic syntheses.¹⁶

Following the old alchemist’s rule ‘similia similibus

solvuntur’ (like dissolves like), we thought that the

introduction of ﬂuorine and perﬂuoroalkyl substituents

into the peripheral phenyl groups of standard betaine

dye 1 should lead to new ‘ﬂuorophilic’ dyes with better

solubility in perﬂuorohydrocarbons. For this reason, we

have synthesized and studied UV–Vis spectroscopically

three new pyridinium N-phenolate betaine dyes 3–5

(Scheme 1) with 20 ﬂuorine substituents (3), ﬁve

triﬂuoromethyl groups (4) and three perﬂuoro-1-hexyl

residues (5).²

There is an additional reason for the preparation of

pyridinium N-phenolate dyes bearing such strongly

electron-withdrawing substituents. In acidic solvents,

betaine dyes 1 and 2 are easily and reversibly protonated

at the phenolic oxygen atom and the long-wavelength

solvatochromic CT absorption band disappears. That is,

E_T(30) values are not directly available for more acidic

solvents. The border between acidic and less acidic

solvents, for which E_T(30) values are available, is

determined by the acidity constant of the corresponding

acid of 1: the pK_aof protonated 1 is 8.65 Æ 0.05¹⁷and

8.63 Æ 0.03¹⁸in water. Replacing the two 2,6-phenyl

groups in the phenolate moiety of 1 by two chlorine

substituents reduces the phenolate basicity by nearly

three orders of magnitude [pK_a= 4.78 for protonated 2,6-

dichloro-4-(2,4,6-triphenylpyridinium-1-yl)phenolate!],

thus allowing the determination of E_Tvalues for more

acidic solvents.¹⁷Introduction of ﬂuorine and ﬂuorine-

containing substituents into the betaine chromophore of 1

should also reduce its phenolate basicity, to give possibly

suitable additional solvatochromic indicator dyes for the

direct determination of E_T(30) values for more acidic

solvents.²

E_T^N E_Tꢀsolvent À E_TꢀTMS=E_Tꢀwater

À E_TꢀTMS

E_Tꢀsolvent À 30:7=32:4

ꢀ2

E_T(30) and E^Nvalues are known for more than 360

solvents and for ^Tmany binary solvent mixtures and also

for other media (e.g. ionic liquids, microheterogeneous

solutions, polymers, surfaces)^3,4(for reviews on empiri-

cal solvent polarity parameters, see Refs. 4b and 10).

These and other empirical parameters of solvent polarity

have been successfully used in the correlation analysis of

solvent inﬂuences on chemical equilibria, reaction rates,

and spectral absorptions^10,11within the framework of so-

called linear free energy relationships.¹²

For UV–Vis spectroscopic solvatochromic measure-

ments, the primary indicator dye 1 is sufﬁciently soluble

in most organic solvents. However, betaine dye 1 is not or

only sparingly soluble in non-polar solvents such as

aliphatic hydrocarbons, perﬂuorohydrocarbons, and TMS

and also in water as a very polar solvent. In order to

obtain betaine dyes with better solubility in water,

pyridyl-substituted pyridinium N-phenolates have re-

cently been synthesized, in which some of the ﬁve

peripheral hydrophobic phenyl groups, surrounding the

zwitterionic chromophore of dye 1, are replaced by

hydrophilic pyridyl groups, thus allowing the study of the

polarity of aqueous electrolyte solutions.¹In order to

obtain pyridinium N-phenolates which are soluble in non-

polar solvents, the lipophilic penta-tert-butyl-substituted

betaine dye 2 (see Scheme 1) was introduced as a

secondary solvatochromic indicator dye.^3bThe excellent

linear correlation between the E_Tvalues of dyes 1 and 2

for those solvents in which both dyes are soluble allows

Copyright  2001 John Wiley & Sons, Ltd.

J. Phys. Org. Chem. 2001; 14: 737–751

NEW F-SUBSTITUTED SOLVATOCHROMIC BETAINE DYES

739

Scheme 2. Synthesis of the eicosan¯uoro 'F₂₀)-substituted betaine dye 3

condensation reaction with sodium nitromalonalde-

hyde,²⁴is converted into the 4-nitrophenol 11.²Reduc-

tion of 11 to 12 and its condensation with pyrylium salt 8

affords N-(4-hydroxyphenyl)pyridinium salt 13, which

is deprotonated with a suspension of (diethylamino-

methyl)polystyrene in dichloromethane to give the F₂₀-

betaine dye 3 as ﬁne violet crystals.

The penta(triﬂuoromethyl)-substituted betaine dye 4 is

synthesized as outlined in Scheme 3. Condensation of

4-(triﬂuoromethyl)acetophenone (14) with 4-(triﬂuoro-

methyl)benzaldehyde gives chalcone 15. This reacts with

ketone 14 in a base-catalyzed Michael addition to the 1,5-

diketone 16, which, on treatment with triphenylcarbe-

nium perchlorate (as hydride acceptor), undergoes ring

closure to the new tris(4-triﬂuoromethylphenyl)-substi-

tuted pyrylium salt 17.

4-(Bromomethyl)-(triﬂuoromethyl)benzene (18) reacts

with diiron nonacarbonyl to afford 4,4'-bis(triﬂuoro-

methyl)-substituted dibenzyl ketone 19, which is con-

verted into the 4-nitrophenol 20 by condensation with

sodium nitromalonaldehyde.²⁴Reduction of 20 to 21, its

condensation with pyrylium salt 17 and deprotonation of

the intermediate pyridinium salt 22 with a suspension of

(diethylaminomethyl)polystyrene in dichloromethane

afford eventually the penta(triﬂuoromethyl)-substituted

betaine dye 4 as ﬁne green crystals.

RESULTS AND DISCUSSION

Syntheses of betaine dyes 3±5

In the synthesis of pyridinium N-phenolate betaine dyes,

the key step is the condensation reaction between 2,4,6-

triaryl-substituted pyrylium salts and 2,6-disubstituted 4-

aminophenols, leading to N-(4-hydroxyphenyl)pyridi-

nium salts, which are eventually deprotonated to afford

the corresponding betaine dyes.^3,19In order to obtain the

desired ﬂuorine-substituted betaine dyes 3–5, the corre-

spondingly substituted pyrylium salts and 4-aminophe-

nols had to be synthesized ﬁrst, most of which were not

known before.

The eicosaneﬂuoro (F₂₀)-substituted betaine dye 3 was

prepared according to Scheme 2. Base-catalyzed con-

densation of pentaﬂuoroacetophenone (6) with benzalde-

hyde gives the corresponding chalcone 7,²⁰which on

treatment with 6 and perchloric acid leads to the

decaﬂuoro-substituted pyrylium salt 8²¹(for reviews on

the synthesis of substituted pyrylium salts, see Ref. 22).

Attempts to obtain analogously the 2,4,6-tris(penta-

ﬂuorophenyl)pyrylium salt with 15 ﬂuorine atoms were

unsuccessful.²

Reaction of (bromomethyl)pentaﬂuorobenzene (9)

with diiron nonacarbonyl affords the decaﬂuoro-substi-

tuted dibenzyl ketone 10,²³which, by a twofold aldol

Finally, the tris(perﬂuorohex-1-yl)-substituted betaine

Copyright  2001 John Wiley & Sons, Ltd.

J. Phys. Org. Chem. 2001; 14: 737–751

¨

C. REICHARDT, M. ESCHNER AND G. SCHAFER

740

Table 1. Long-wavelength solvent-dependent CT absorption maxima, l_max'nm), and the corresponding E_T'X) values

'kcal mol^À1; in parentheses) of betaine dyes X = 3±5, measured in up to 40 solvents of different polarity at 25°C and normal

pressure, ordered according to decreasing E_T'30) values^4b

Solvent

E_T(30)^a

l

_max(3) [E_T(3)]^b

l

_max(4) [E_T(4)]^b

l

_max(5) [E_T(5)]^b

HFIP^c

(65.3)^c

59.8

59.6

56.3

–

443 (64.5)

467 (61.2)

471 (60.7)

483 (59.2)

484 (59.1)^d

492 (58.1)

489 (58.5)

515 (55.5)

503 (56.8)

506 (56.5)

509 (56.2)^d

512 (55.8)

524 (54.6)

533 (53.6)

539 (53.0)

543 (52.7)

542 (52.7)

537 (53.2)

546 (52.4)

542 (52.7)

549 (52.1)

566 (50.5)

–

2,2,2-Triﬂuoroethanol

2-Cyanoethanol

Ethane-1,2-diol

3-Chlorophenol

Formamide

e

55.8

55.4

54.1

(43.9)

52.0^f

51.9

50.7

49.7

49.1

49.0

48.8

48.6

48.5

48.4

48.1

47.1

46.3

45.6

45.1

43.3^f

43.2

42.9

42.2

41.3

41.0

40.9

40.7

40.5

39.1

38.4

38.1

38.0

37.4

37.1

36.6

36.2

36.0

34.5

34.3

34.2

33.9

33.2

533 (53.6)

521 (54.9)

559 (51.1)

–

Methanol

562 (50.9)

2,2,2-Trichloroethanol

N-Methylformamide

Acetic anhydride

N-Methylacetamide

Ethanol

597 (47.9)

–

1-Propanol

563 (50.8)

574 (49.8)

–

620 (46.1)

632 (45.2)

–

1-Butanol

1-Pentanol

3-Methyl-1-butanol

1-Hexanol

–

582 (49.1)

–

642 (44.5)

–

2-Methyl-1-propanol

1-Heptanol

2-Propanol

1-Octanol

2-Butanol

Nitromethane

Acetonitrile

582 (49.1)

589 (48.5)

–

643 (44.5)

651 (43.9)

–

609 (46.9)

632 (45.2)

628 (45.5)

–

674 (42.4)

687 (41.6)

691 (41.4)

692 (41.3)

–

579 (49.4)

581 (49.2)

610 (46.9)^f

589 (48.5)

600 (47.6)

603 (47.4)

660 (43.3)

638 (44.8)

610 (46.9)

660 (43.3)

671 (42.6)

638 (44.8)

680 (42.0)

655 (43.7)

669 (42.7)

–

Dimethyl sulfoxide

2-Methyl-2-propanol

N,N-Dimethylformamide

N,N-Dimethylacetamide

Acetone

1,2-Dichloroethane

Morpholine

HMPT

Dichloromethane

1-Chloro-3,3,3-triﬂuoropropane

Pyridine

Trichloromethane

1,2-Dimethoxybenzene

Ethyl acetate

1,2-Dichlorobenzene

Tetrahydrofuran

Methoxybenzene

Ethoxybenzene

1,1,1-Trichloroethane

1,4-Dioxane

–

654 (43.7)

673 (42.5)

–

731 (39.1)

753 (38.0)

–

719 (39.8)

–

780 (36.7)

–

754 (37.9)

735 (38.9)

775 (36.9)

749 (38.2)

792 (36.1)

797 (35.9)

801 (35.7)

808 (35.4)

820 (34.9)

843 (33.9)

839 (34.1)

848 (33.7)

845 (33.8)

832 (34.4)

826 (34.6)

847 (33.8)

839 (34.1)

861 (33.2)

867 (33.0)

871 (32.8)

870 (32.9)

–

711 (40.2)

724 (39.5)

711 (40.2)

e

–

e

Diethyl ether

Benzene

Hexaﬂuorobenzene

Toluene

Ethylbenzene

–

915 (31.2)

–

912 (31.3)

925 (30.9)

918 (31.1)

e

–

e

–

e

–

e

–

a

Taken from Refs 2 and 4b.

b

The E_T(X) values given in parentheses are calculated from the visible absorption maxima of X = 3–5 according to Eqn. (1).

c

d

e

f

HFIP = 1,1,1,3,3,3-hexaﬂuoro-2-propanol; the E_T(30) value for HFIP is taken from Ref. 13.

Measured at 36°C.

Not soluble in this solvent.

Measured at 30°C.

dye 5 was synthesized as shown in Scheme 4. Alkylation

kylation of ethyl 4-bromobenzoate (26), prepared from

acid 25 with triethyloxonium tetraﬂuoroborate,²⁷with

perﬂuoro-1-iodohexane affords the (perﬂuorohex-1-yl)-

substituted ester 27.^25,26Reduction of this ester with

of 4-iodoacetophenone (23) with perﬂuoro-1-iodohexane

in the presence of copper bronze in DMSO yields 4-

(perﬂuorohex-1-yl)acetophenone 24.^25,26Analogous al-

Copyright  2001 John Wiley & Sons, Ltd.

J. Phys. Org. Chem. 2001; 14: 737–751

NEW F-SUBSTITUTED SOLVATOCHROMIC BETAINE DYES

741

Scheme 3. Synthesis of the penta'tri¯uoromethyl)-substituted betaine dye 4

lithium aluminum hydride to the benzyl alcohol 28,

followed by its oxidation with pyridinium ﬂuorochro-

mate,²⁸affords the substituted benzaldehyde 29.

Table 1 and Experimental section. Only the position of

the long-wavelength absorption band is strongly solvent-

(and substituent-) dependent; the others are not. Quantum

chemical calculations show that this absorption band is

related to an intramolecular charge-transfer (CT) from

the HOMO of the phenolate to the LUMO of the

pyridinium moiety (for various quantum chemical

calculations on the standard betaine dye 1, see Ref. 29).

For this reason, the position of the long-wavelength CT

band should depend on the ionization energy of the

electron donor (i.e. the phenolate part) and on the

electron afﬁnity of the electron acceptor (i.e. the

pyridinium part). On protonation of the phenolate part

of dyes 3–5, the solvent-dependent CT band disappears

and the corresponding N-(hydroxyphenyl)pyridinium

salts formed (e.g. 13, 22, and 32) absorb at l_maxꢁ 295–

330 nm (ꢁ = 30 000–40 000 l mol^À1cm^À1), correspond-

ing to a local p–p* absorption of the 2,4,6-triarylpy-

ridinium chromophore. Therefore, betaine dyes 3–5 and

also 1 and 2 cannot be used as polarity indicators in acidic

solvents such as carboxylic acids.

Condensation of ketone 24 with aldehyde 29 leads to

chalcone 30, which on reaction with 24 in the presence of

perchloric acid²²gives the new pyrylium salt 31.

Eventually, condensation of pyrylium salt 31 with 4-

amino-2,6-diphenylphenol^3a,19to the pyridinium salt 32

and its deprotonation with sodium methanolate in

methanol afford the desired tris(perﬂuorohexyl)-substi-

tuted betaine dye 5 as ﬁne dark-green crystals.

The molecular structures of all new compounds were

conﬁrmed by elemental analysis and UV–Vis, IR, mass,

and NMR spectra (see Experimental section).

UV±Vis spectra and solvatochromism of betaine

dyes 3±5

In acetonitrile, a solvent of intermediate polarity, the

UV–Vis spectra of the new betaine dyes 3–5 exhibit

three main absorption bands of different intensity:

at l_maxꢁ 580–690 nm (e ꢁ 1200–7400 l mol^À1cm^À1),

Introduction of three strongly electron-withdrawing

perﬂuoro-1-hexyl substituents into the three 2,4,6-

triphenyl rings of the pyridinium part of betaine dye 1

to give 5 should increase the electron afﬁnity of the

325–380 nm (e ꢁ 12 000–30 000 l mol^À1cm^À1

)

and

230–295 nm (e ꢁ 26 000–37 000 l mol^À1cm^À1); see

Copyright  2001 John Wiley & Sons, Ltd.

J. Phys. Org. Chem. 2001; 14: 737–751

¨

742

C. REICHARDT, M. ESCHNER AND G. SCHAFER

Scheme 4. Synthesis of the tris'trideca¯uoro-1-hexyl)-substituted betaine dye 5

pyridinium moiety, with a signiﬁcant bathochromic CT

band shift as consequence. This is indeed the case: on

going from betaine dye 1 to dye 5, a bathochromic CT

band shift of Dl = 64 nm (DE_T= À4.2 kcal mol^À1) is

observed in acetonitrile as solvent (cf. Table 1). In

contrast, a large hypsochromic CT band shift of

Dl = À48 nm (DE_T= 3.8 kcal mol^À1) is observed in

acetonitrile on going from betaine dye 1 to dye 3 with

altogether 20 electron-withdrawing ﬂuorine substituents,

half of them in the pyridinium and half in the phenolate

part. This means that the 10 electron-withdrawing

ﬂuorine substituents located in the phenolate part of

dye 3, causing an increase in its ionization energy, exceed

the inﬂuence of the other 10 ﬂuorine atoms in the

pyridinium moiety of 3 on the electron afﬁnity of that part

of the dye molecule. On going from betaine dye 1 to dye

4 with ﬁve peripheral triﬂuoromethyl substituents, there

is only a very small bathochromic CT band shift of

Dl = 5 nm (DE_T= À0.4 kcal mol^À1) observed in aceto-

nitrile. Obviously, in this case the electron-withdrawing

inﬂuence of the three CF₃groups in the pyridinium part

and that of the two CF₃groups in the phenolate part are

practically equal and an electronically balanced situation

results.

Copyright  2001 John Wiley & Sons, Ltd.

J. Phys. Org. Chem. 2001; 14: 737–751

NEW F-SUBSTITUTED SOLVATOCHROMIC BETAINE DYES

743

than the already published value of 65.3 kcal mol^{À1 4b,13}

.

Table 2. Regression parameters for the linear correlations

between the E_T'X) values of betaine dyes X = 3±5 and the E_T

'30) values of the standard betaine dye 1^4baccording to

the correlation equation E_T'X) 'kcal mol^À1) = aE_T'30)

'kcal mol^À1) b

The latter value is, however, not the result of a direct

measurement; it was obtained by extrapolation of

the l_max(1) values of 2-propanol–HFIP and (n-

Bu)₄N HO^À–HFIP mixtures.¹³The E_T(30) value of

X

a

b

n^a

r^b

s[E_T(X)]^c

62.1 kcal mol^À1for HFIP, which is smaller than that of

water (63.1 kcal mol^À1), seems to be the more reliable

one, based directly on the solvatochromism of betaine

dye 3. As a control, the E_T(30) value of 2,2,2-

triﬂuoroethanol (TFE) analogously calculated from E_T

(3) amounts to 58.5 kcal mol^À1, which is in satisfactory

agreement with the directly measured value of

59.8 kcal mol^À1(Table 1).

3

4

5

0.926

0.961

0.902

7.04

1.38

0.22

37

28

26

0.986

0.992

0.997

1.04

0.86

0.45

a

Number of solvents.

b

c

Correlation coefﬁcient.

Standard deviation of the estimate in kcal mol^À1

.

Using the E_T(3) value of 3-chlorophenol (pK_a

= 9.1^30b) given in Table 1, in the same way an E_T(30)

value for this solvent can be calculated. The E_T(30) value

of 56.2 kcal mol^À1found for 3-chlorophenol ﬁts fairly

well into the values of a whole series of other substituted

phenols, determined in a different manner;³¹however, it

is in disagreement with another published value³²for this

solvent (60.8 kcal mol^À1).

In Table 1, the molar transition energies E_T(3), E_T(4),

and E_T(5) of the new betaine dyes 3–5, measured for

up to 40 hydrogen-bond donor (HBD) and non-HBD

solvents, are also given, together with the corresponding

E_T(30) values of the primary indicator dye 1. In all three

cases there is a good linear correlation between the E_T

values of the new dyes 3–5 and the E_T(30) values of dye

1 with correlation coefﬁcients r ꢁ 0.99, as shown by the

regression parameters compiled in Table 2. The slope of

all three regression lines, a ꢁ 0.9, is slightly smaller than

unity, indicating that the new solvatochromic betaine

dyes 3–5 are less sensitive to a change in solvent polarity

than standard dye 1. The good quality of the correlation

equations in Table 2 should allow the calculation of E_T

(30) values for such media, for which a direct experi-

mental determination is not possible for reasons of

limited solubility or strong acidity, in this way using the

new dyes 3–5 as tertiary standard dyes in addition to the

secondary standard dye 2.

The introduction of the electron-withdrawing ﬂuorine

and perﬂuoroalkyl substituents into the peripheral phenyl

groups of dye 1 leads to a reduced basicity of the

pyridinium N-phenolate and betaine dyes 3–5 are less

prone to protonation in more acidic solvents. This can be

well seen from solutions of their protonated precursors

13, 22, and 32 (Schemes 2 and 3) in methanol: even in the

absence of bases, these solutions are already reddish

because partial ionization of the N-(4-hydroxyphenyl)-

pyridinium salts produces small amounts of the corre-

sponding betaine dyes 3–5, the solutions of which in

methanol are red (l_max= 489, 521, and 562 nm, respec-

tively; Table 1). The phenolic OH group in 13, 22, and 32

is more acidic than in protonated 1 because of the strong

ÀI effect of the ﬂuorine and perﬂuoroalkyl substituents.

The E_T(30) value of 1,1,1,3,3,3-hexaﬂuoro-2-propanol

(HFIP) is not directly measurable with dye 1 because of

the high acidity of this solvent (pK_a= 9.3^30a). However,

the F₂₀betaine dye 3 is not protonated in this solvent and

the CT absorption band at l_max= 443 nm can be observed

(Table 1). With the corresponding E_T(3) value of

64.5 kcal mol^À1and the ﬁrst correlation equation given in

Table 2, an E_T(30) value of 62.1 kcal mol^À1can be

calculated for HFIP. This value is surprisingly smaller

With the E_T(3) value of acetic anhydride given in

Table 1, an E_T(30) value for this problematic solvent can

be analogously calculated. The E_T(30) value found for

acetic anhydride in this way, 53.4 kcal mol^À1, is higher

than the published value of 43.9 kcal mol^{À1 3b,4b}

Again,

.

the already published much lower value was not directly

measured, but was calculated from Kosower’s Z values³³

by means of a correlation equation established by

Grifﬁths and Pugh [E_T(30) = 0.752 Z À7.87] with 15

carefully selected solvents.³⁴In more acidic solvents, in

which even the new betaine dyes 3–5 are protonated, the

correlation equation introduced by Grifﬁths and Pugh is

still the only means to obtain calculated E_T(30) values

for such solvents (e.g. carboxylic acids^3b,4b), since Z

values are directly measurable in acids.

Solvatochromic dyes such as 1 and 2 can also be used

as probe molecules for the determination of the polarity

of solid surfaces^35,37and of solid materials such as

various polymers.^36,37In addition to standard dyes 1 and

2, the F₂₀betaine dye 3 has also stood its ‘acid test’ as a

surface polarity indicator: adsorbed on the solid material,

dye 3 has already been used for the determination of the

surface polarity of various solid acids such as bare and

functionalized silicas, aluminas, alumosilicates, titanium

dioxides^37aand polysaccharides^37band, dissolved in thin,

transparent polymer ﬁlms, for measurements of the

polarity of different synthetic polymers and copoly-

mers.^37cFor example, the E_T(30) values of the surfaces

of Al₂O₃(Condea) and TiO₂(Anatas; Condea) are 57.3

and 59.7 kcal mol^À1, respectively.^37aThat is, the surface

polarity of these oxides corresponds to the polarity of

alcohols such as glycerol (57.0) and 2,2,2-triﬂuoroetha-

nol (59.8).

To our disappointment, it was not possible to

determine indirectly by means of the ‘ﬂuorophilic’ new

betaine dyes 3–5 the E_T(30) values of perﬂuoroalkanes,

Copyright  2001 John Wiley & Sons, Ltd.

J. Phys. Org. Chem. 2001; 14: 737–751

¨

C. REICHARDT, M. ESCHNER AND G. SCHAFER

744

using the correlation equations given in Table 2. As least

polar solvents, they should have E_T(30) values of less

than ca 30–31 kcal mol^À1as found for alkanes and TMS.

All three dyes 3–5 are surprisingly not soluble in solvents

such as perﬂuorohexane, perﬂuorooctane, perﬂuoro-

(methylcyclohexane) and perﬂuorodecalin. Because of

the high electronegativity of ﬂuorine atoms and their very

small polarizability, the dispersion interactions between

perﬂuoroalkanes and the zwitterionic dyes are not

sufﬁcient to break down the crystal lattice of the highly

dipolar betaine dyes. Even common organic solvents are

not miscible with perﬂuoroalkane solvents. Maybe the

additional introduction of sterically demanding substi-

tuents such tert-butyl or 1-adamantyl into betaine dyes 3–

5, thus weakening the strong dye–dye interactions in the

crystal lattice, can lead to solvatochromic dyes capable of

measuring empirically the polarity of perﬂuoroalkanes.

puriﬁed by means of molecular sieves and, if necessary,

by ﬁltration through a column of basic aluminum oxide

(B-Super I), in order to remove traces of acids. For these

measurements the solvents must be water free and

absolutely acid free. Solvents for the synthetic work

were puriﬁed according to the usual standard methods.³⁸

Synthesis of betaine dye 3 5Scheme 2). 1-Penta¯uoro-

phenyl-3-phenylprop-2-en-1-one ꢀ7). To an ice-cold

solution of NaOH (0.25 g, 8.25 mmol) in water (11 ml)

and ethanol (9 ml; 96%, v/v) were added acetylpenta-

ﬂuorobenzene (6) (5.00 g, 23.8 mmol) and freshly

distilled benzaldehyde (2.78 g, 25.2 mmol). After stirring

at room temperature for 1 h, the precipitate formed was

ﬁltered off, washed with water, dried in vacuo with

P₄O₁₀, and recrystallized from a small amount of ethanol

(96%), to give the chalcone 7 (6.50 g, 95%) as colorless

needles with m.p. 101°C (lit.²⁰102–103°C).

2,6-Diꢀpenta¯uorophenyl)-4-phenylpyrylium perchlo-

rate ꢀ8). To a stirred mixture of ketone 6 (4.21 g,

20.0 mmol) and chalcone 7 (5.73 g, 20.0 mmol) was

added at 80°C dropwise and carefully aqueous perchloric

acid (70%, w/w; 6.32 g, 44.0 mmol) and then the mixture

was kept at 100°C for 2 h. After cooling to room

temperature, diethyl ether (ca 100 ml) was added, the

precipitate formed was ﬁltered off, washed with diethyl

ether, and recrystallized from acetic acid, to give, after

drying in vacuo with KOH, the pyrylium salt 8 (7.69 g,

74%) as yellow crystals with m.p. 250°C (lit.²¹249–

251°C).

CONCLUSION

The new betaine dyes 3–5, synthesized according to

Schemes 2–4, enlarge the supply of highly solvatochro-

mic indicator dyes which can be used, in addition to the

known standard betaine dyes 1 and 2, to extend the E_T

(30) scale of solvent polarity by new solvents of interest.

Dyes 3–5 are particularly useful for the indirect

determination of E_T(30) values of more acidic solvents,

polymers and solid surfaces, with which 1 and 2 are

protonated. Disappointingly, in spite of the introduction

of ﬂuorine and perﬂuoroalkyl substituents, they are still

not sufﬁciently soluble for UV–Vis spectroscopic

measurements in perﬂuoroalkanes, for which E_T(30)

values are still lacking.

1,3-Diꢀpenta¯uorophenyl)propan-2-one ꢀ10). A solu-

tion of (bromomethyl)pentaﬂuorobenzene 9 (13.64 g,

52.3 mmol; Aldrich; caution: lachrymator!) and diiron

nonacarbonyl (19.00 g, 52.3 mmol) in dry benzene

(200 ml) was heated under reﬂux under nitrogen for

3 h. After cooling to room temperature, the precipitate

formed (FeBr₃) was ﬁltered off and extracted four times

with boiling benzene. The ﬁltrate and the four extracts

were combined and the benzene was distilled off

[caution: the benzene contains toxic Fe (CO)₅!]. The

solid residue was puriﬁed by column chromatography

with neutral alumina (activity grade III) and benzene–

light petroleum (b.p. 40–60°C) (1:9) as eluent (R_f= 0.16)

and then recrystallized from n-hexane to afford the

ketone 10 (6.00 g, 63%) as ﬁne colorless needles with

m.p. 100°C (lit.^23a,b104°C). ¹³C NMR (CDCl₃): ꢂ

(ppm) = 35.7 (CH₂), 107.4 (quaternary phenyl-C), 136.0–

EXPERIMENTAL

General methods. Melting-points (not corrected):

Koﬂer-Mikroheiztisch (Reichert). Elemental analyses:

Analytik-Servicelabor of the Department of Chemistry,

Marburg, and Mikroanalytisches Laboratorium Malissa-

Reuter, Engelskirchen-Elbach. UV–Vis spectra: U-3410

double-beam UV–Vis–NIR spectrophotometer (Hitachi)

with thermostated 1.00 cm quartz cells. IR spectra: IFS-

88 spectrophotometer (Bruker) with KBr discs. NMR

spectra: AM-300 and WM-400 spectrometers (Bruker),

with TMS and trichloroﬂuoromethane as internal stan-

dards. Mass spectra: MAT CH-7A spectrometer (Varian)

with electron ionization (EI, 70 eV) and MAT 711 spec-

trometer (Varian) with ﬁeld desorption (FD). Column

chromatography: silica gel 60 (Merck), particle size

0.063–0.200 mm, and N-Super I and B-Super I aluminum

oxide (ICN Biomedicals). Solvents: solvents for the

solvatochromic measurements were used as supplied

commercially in the highest quality available (analytical

or spectroscopic grade) and were additionally dried and

147.0 (phenyl-C), 197.0 (C=O).

4-Nitro-2,6-diꢀpenta¯uorophenyl)phenol ꢀ11). To a

stirred solution of NaOH (1.28 g, 32.0 mmol) in water

(48 ml) and ethanol (112 ml; 96%, v/v) was added ketone

10 (12.08 g, 32.0 mmol) and sodium nitromalonaldehyde

monohydrate (4.56 g, 32.0 mmol)²⁴and the mixture was

stirred at room temperature over a period of 15 days.

Copyright  2001 John Wiley & Sons, Ltd.

J. Phys. Org. Chem. 2001; 14: 737–751

NEW F-SUBSTITUTED SOLVATOCHROMIC BETAINE DYES

745

Then, the solution was acidiﬁed (pH ꢁ 1) and some water

was added in order to complete the precipitate formation.

The precipitate formed was ﬁltered off, washed acid free

with water, and dried with P₄O₁₀in vacuo to afford the

nitrophenol 11 (14.40 g, 96%), which is sufﬁciently pure

for the next step. Analytically pure 11 was obtained by

recrystallization of a small sample from 1,2-dichloro-

benzene to give light-yellow crystals with m.p. 210°C. IR

(KBr): ꢀeꢀcm^À1 3459 (OH), 1519 and 1349 (NO₂).

UV–Vis (CH₃OH): l_max(log ꢁ) = 388 (4.29), 316 (3.96),

221 (4.27), 181 nm (3.70). ¹H NMR (CD₃CN): ꢂ

(ppm) = 8.09 (broad s, OH), 8.39 (s, 2 H. aromatic H).

¹³C NMR (CD₃SOCD₃): ꢂ (ppm) = 110.3 (quat. C₆F₅-C),

115.3 (quat. phenol-C-2), 129.1 (phenol-C-3), 137.1–

144.3 (C₆F₅-C and phenol-C-4), 159.3 (C–OH). ¹⁹F

130.6 (phenyl-C-2), 131.0 (phenyl-C-3), 131.1 (phenol-

C-3), 131.8 (pyridinium-C-3), 133.3 (pyridinium-C-4),

1

135.3 (phenyl-C-4), 140.5 (d, J_CF= 248 Hz), 146.0

1

(phenol-C-4), 146.7 (d, J_CF= 255 Hz), 147.4 (d,

¹J_CF= 240 Hz), 157.2 (pyridinium-C-2), 161.1 (C-OH).

¹⁹F NMR (CD₃COCD₃): ꢂ (ppm) = À134.6 (2 F), À141.8

(2 F), À148.3 (1 F), À154.5 (1 F), À161.0 (2 F), À163.2

(2 F). MS (FD): m/z (%) = 911 (14) [M ÀHClO₄], 891

(100) [M ÀHClO₄ÀHF]. C H ClF NO 0.5H O

₅Á

41 10

20

2

(1012.0 9.0 = 1021.0): calcd C 48.23, H. 1.09, N 1.37;

found C 48.31, H 1.19, N 1.48%.

4-[2,6-Diꢀpenta¯uorophenyl)-4-phenylpyridinium-1-

yl]-2,6-diꢀpenta¯uorophenyl)phenolate ꢀ3) ꢀ`F₂₀-be-

taine'). To a stirred solution of perchlorate 13 (1.00 g,

0.98 mmol) in dry dichloromethane (30 ml) was added

the granulated polymer base (diethylaminomethyl)

polystyrene (Fluka; 0.84 g, base equivalent 2.52 mmol)

and the suspension was stirred for 30 min at room

temperature. Then, the polymer base was ﬁltered off,

washed with dichloromethane and discarded. The solvent

of the combined ﬁltrates was distilled off in vacuo to

afford betaine dye 3 (0.70 g, 77%) as ﬁne hygroscopic

violet crystals, which on heating melted at ca 186°C and

decomposed at ca 190°C. UV–Vis (CH₃CN): l_max(log

ꢁ) = 579 (3.50), 325 nm (4.49). ¹H NMR (CD₃COCD₃): ꢂ

(ppm) = 7.28 (s, 2 H, phenolate-3-H), 7.69–8.32 (m, 5 H,

phenyl-H), 9.31 (s, 2 H, pyridinium-3-H). ¹³C NMR

(CD₃COCD₃): ꢂ (ppm) = 108.4, 110.2, 117.2, 130.3,

130.5, 131.0, 131.1, 131.8, 133.3, 135.3, 137–146 (six

broad m of low intensity; pentaﬂuorophenyl-C), 146.9,

157.2, 161.1 (C—O^À). ¹⁹F NMR (CD₃COCD₃): ꢂ

(ppm) = À136.6 (2 F), À142.8 (2 F), À149.8 (1 F),

NMR (CD₃COCD₃):

ꢂ

(ppm) = À139.9 (ortho-F),

À155.0 (para-F), À163.2 (meta-F). MS (FD): m/z

(%) = 471 (100) [M ]. C₁₈H₃F₁₀NO₃(471.2): calcd C

45.88, H 0.64, N 2.97; found C 46.08, H 0.61, N 3.03%.

4-Amino-2,6-diꢀpenta¯uorophenyl)phenol ꢀ12). A sus-

pension of a palladium catalyst (10% Pd on charcoal, ca

100 mg) in a solution of nitrophenol 11 (4.70 g,

10.0 mmol) in ethanol (100 ml, 96%, v/v) was reduced

with dihydrogen at room temperature and normal

pressure until the necessary amount of H₂was absorbed.

Under nitrogen, the catalyst was ﬁltered off and the

solvent was distilled off in vacuo to give 12 (4.30 g, 98%)

as a beige powder with m.p. 160–165°C, which turned

dark on air. Because of its sensitivity to oxygen, 12 was

immediately converted into the pyridinium salt 13

without detailed further characterization. ¹H NMR

(CD₃COCD₃): ꢂ (ppm) = 3.42 (s, 2 H, NH₂), 6.71 (s, 2

H, aromatic H); the OH signal was not detected.

À158.4 (1 F), À161.9 (2 F), À165.4 (2 F). MS (FD): m/z

(%) = 911 (100) [M ]. C H F NO H O (911.5

Á

41

9

20

2

2,6-Diꢀpenta¯uorophenyl)-4-phenyl-1-[4-hydroxy-3,5-

diꢀpenta¯uorophenyl)phenyl]pyridinium perchlorate

ꢀ13). A solution of freshly prepared aminophenol 12

(4.42 g, 10.0 mmol), pyrylium salt 8 (4.31 g, 8.33 mmol)

and water-free sodium acetate (1.71 g, 20.8 mmol) in dry

ethanol (100 ml) was heated under reﬂux for 2.5 h. Then,

at room temperature, the solution was acidiﬁed (pH ꢁ 1)

by addition of a few drops of aqueous HClO₄(70%, w/w)

and the product was precipitated by addition of water.

The precipitate formed was ﬁltered off, washed acid free

with water, and dried with P₄O₁₀in vacuo. The product

was dissolved in ethanol (96%) and precipitated by

addition of n-hexane. This procedure was repeated to

afford 13 (3.19 g, 31%) as ﬁne brownish crystals with

m.p. 194–196°C. IR (KBr): ꢀe ꢀcm^À1 3307 (OH),

1119 (ClO₄). UV–Vis (CH₃CN): l_max(log ꢁ) = 332

(4.47), 218 nm (4.70). ¹H NMR (CD₃COCD₃): ꢂ

(ppm) = 7.68–7.82 and 8.34 (m, 5 H, 4-phenyl-H), 7.93

(s, 2 H, phenol-3-H), 9.38 (s, 2 H, pyridinium-3-H), 9.79

(broad s, 1 H, OH). ¹³C NMR (CD₃COCD₃): ꢂ

(ppm) = 108.3 (quat. C₆F₅-C), 110.5 (quat. C₆F₅-C),

117.3 (quat. phenol-C-2), 130.3 (quat, phenyl-C-1),

18.0 = 929.5): calcd C 52.98, H 1.19, N 1.51, F 40.88;

found C 52.87, H 1.18, N 1.55, F 41.04%.

Synthesis of betaine dye 4 5Scheme 3). 1,3-Di[4-

ꢀtri¯uoromethyl)phenyl]-prop-2-en-1-one ꢀ15). To a

stirred solution of NaOH (5.12 g, 128 mmol) in water

(20 ml) and ethanol (20 ml; 96%, v/v) were added 4-

(triﬂuoromethyl)acetophenone 14 (18.82 g, 100 mmol)

and

4-(triﬂuoromethyl)benzaldehyde

(17.42 g,

100 mmol). After stirring at room temperature for 2 h,

the precipitate formed was ﬁltered off, washed with

water, and dried with P₄O₁₀in vacuo, to give ketone 15

(30.97 g, 90%) as crude product, sufﬁciently pure for the

next reaction step. Analytically pure 15 was obtained by

sublimation at 130°C/10^À3Torr (1 Torr = 133.3 Pa) as

yellow crystals with m.p. 98–100°C. IR (KBr):

ꢀeꢀcm^À1 1670 (C

=

O). ¹H NMR (CDCl₃):

ꢂ

(ppm) = 7.56 (d, ³J = 15.8 Hz, 1 H, CO–CH

=CH),

3

7.51–7.81 (m, 4 H, aromatic H), 7.84 (d, J = 15.8 Hz,

1 H, CO–CH=CH), 8.05 and 8.12 (m, 4 H, aromatic H).

1

¹³C NMR (CDCl₃): ꢂ (ppm) = 123.6 (q, J_CF= 270 Hz,

CF₃), 123.8 (q, ¹J_CF= 270 Hz, CF₃), 125.7, 126.0, 128.6,

Copyright  2001 John Wiley & Sons, Ltd.

J. Phys. Org. Chem. 2001; 14: 737–751

¨

C. REICHARDT, M. ESCHNER AND G. SCHAFER

746

2

128.8, 132.2 (q, J_CF= 30.0 Hz, C–CF₃), 134.3 (q,

²J_CF= 30.0 Hz, C–CF₃), 137.8, 140.6, 143.7 (CO–

one C–CF₃), 136.1 (q, ²J_CF= 30 Hz, two C–CF₃), 137.6,

167.4 (pyrylium-C-4), 171.8 (pyrylium-C-2). ¹⁹F NMR

(CD₃COCD₃): ꢂ (ppm) = À62.9 (s, one CF₃), À63.0 (s,

CH=CH), 189.1 (C=

O). ¹⁹F NMR (CDCl₃): ꢂ

(ppm) = À63.4 (s, CF₃), À63.6 (s, CF₃). MS (FD): m/z

two CF₃). MS (FD): m/z (%) = 513 (67) [M ÀClO₄].

(%) = 344 (100) [M ]. C₁₇H₁₀F₆O (344.3): calcd C

C₂₆H₁₄ClF₉O₅(612.8): calcd C 50.96, H 2.30; found C

50.95, H 1.98%.

59.31, H 2.93; found C 59.22, H 2.34%.

1,3,5-Tris[4-ꢀtri¯uoromethyl)phenyl]pentan-1,5-dione

ꢀ16). To a reﬂuxing suspension of sodium hydride

(6.48 g, 216 mmol; from an 80% suspension of NaH in

light petroleum) in dry benzene (100 ml) was added a

solution of chalcone 15 (29.98 g, 87.0 mmol) and 4-

(triﬂuoromethyl)acetophenone 14 (16.29 g, 87.0 mmol)

in dry benzene (300 ml) and the mixture was heated

under reﬂux for 3 h. After cooling to room temperature,

crushed ice was carefully added to the reddish brown

solution and the solution was acidiﬁed (pH ꢁ 1) with

aqueous 2 M HCl. The organic phase was separated and

the aqueous phase was extracted four times with diethyl

ether. The combined organic extracts were washed acid

free with water and dried with MgSO₄. After ﬁltration,

the solvents were distilled off in vacuo and the solid

residue was recrystallized from light petroleum (b.p. 40–

60°C) to afford 16 (32.60 g, 70%) as brownish crystals,

which were sufﬁciently pure for the next reaction step.

Analytically pure, colorless 16 was obtained after further

1,3-Di[4-ꢀtri¯uoromethyl)phenyl]propan-2-one ꢀ19). A

solution of 4-(bromomethyl)-(triﬂuoromethyl)benzene

18 (9.56 g, 40.0 mmol; Aldrich; caution: lachrymator!)³⁹

and diiron nonacarbonyl (21.84 g, 60.0 mmol) in dry n-

octane (200 ml) was heated under reﬂux under nitrogen

for 18 h. After cooling to room temperature, the

precipitate formed (FeBr₃) was ﬁltered off and extracted

ﬁve times with boiling toluene. The ﬁltrate and the ﬁve

extracts were combined and the solvents were distilled

off [caution: the solvents contain toxic Fe(CO)₅!]. The

solid residue was puriﬁed by column chromatography

with neutral alumina (activity grade III) and diethyl

ether–light petroleum (b.p. 40–60°C) (2:5) as eluent.

From the second fraction the solvents were distilled off to

afford ketone 19 (4.78 g, 70%) as colorless needles with

1

m.p. 63–67°C (lit.⁴⁰63–67°C). H NMR (CDCl₃): ꢂ

(ppm) = 3.82 (s, 4 H, CH₂), 7.26 and 7.58 (AA BB, 8 H,

aromatic H). ¹³C NMR (CDCl₃): ꢂ (ppm) = 49.0 (CH₂),

1

3

124.1 (q, J_CF= 272 Hz, CF₃), 125.7 (q, J_CF= 3.7 Hz,

2

recrystallization from cyclohexane with m.p. 120–

C=

C–CF₃), 129.7 (q, J_CF= 33 Hz, C–CF₃), 129.9

1

121°C. IR (KBr): ꢀe ꢀcm^À1 1697 (C

=

O). H NMR

(aromatic C), 137.5 (aromatic C–CH₂), 203.4 (C O).

=

(CDCl₃): ꢂ (ppm) = 3.47 and 3.60 (AB part of ABX

system, ³J_AB= 17.3 Hz, 4 H, CH₂), 4.20 (X part of ABX

4-Nitro-2,6-di[4-ꢀtri¯uoromethyl)phenyl]phenol ꢀ20).

To a stirred solution of NaOH (0.56 g, 14.1 mmol) in

water (9 ml) and ethanol (45 ml; 96%, v/v) were added

ketone 19 (4.87 g, 14.1 mmol) and sodium nitromalon-

aldehyde monohydrate (1.35 g, 14.2 mmol)²⁴and the

mixture was stirred at room temperature for 24 h. Then

the solution was acidiﬁed with aqueous 2 M HCl (pH ꢁ 1)

and some water was added in order to complete the

formation of a precipitate (which sometimes came as an

oil). The suspension was extracted eight times with

diethyl ether (8 Â 50 ml). The combined ether extracts

were washed acid free with water and dried with MgSO₄.

The ether was distilled off and the residue was puriﬁed by

column chromatography with silica gel and toluene as

eluent (R_f= 0.43). Removal of the toluene from the eluate

by distillation yielded a viscous yellow oil, still contain-

ing some toluene, which was removed by drying in vacuo

at 80°C/10^À3Torr, to afford nitrophenol 20 (4.04 g, 68%)

as sand-colored microcrystals with m.p. 114–116°C. IR

(KBr): ꢀeꢀcm^À1 3450 (OH), 1514 and 1325 (NO₂). ¹H

NMR (CDCl₃): ꢂ (ppm) = 5.90 (s, 1 H, OH), 7.70 and

8.04 (AA BB, 4 H, phenyl-H), 8.32 (s, 2 H, phenol-3-H).

3

system, J_AX= 12.3 Hz, J_BX= 1.4 Hz, 1 H, CH), 7.47

and 7.59 (AA BB, 4 H, aromatic H), 7.76 and 8.08 (AA

BB, 8 H, aromatic H). ¹³C NMR (CDCl₃): ꢂ (ppm) = 36.5

1

(CH), 44.6 (CH₂), 123.5 (q, J_CF= 272 Hz, CF₃), 123.8

1

(q, J_CF= 273 Hz, CF₃), 125.8, 127.9, 128.4, 129.3 (q,

²J_CF= 32.5 Hz, C–CF₃), 134.7 (q, J_CF= 32.5 Hz, C–

2

CF₃), 139.2, 147.3, 196.9 (C=

O). ¹⁹F NMR (CDCl₃): ꢂ

(ppm) = À62.7 (s, 3 F, CF₃), À63.3 (s, 6 F, CF₃). MS

(FD): m/z (%) = 532 (100) [M ]. C₂₆H₁₇F₉O₂(532.4):

calcd C 58.66, H 3.22; found C 58.80, H 3.44%.

2,4,6-Tris[4-ꢀtri¯uoromethyl)phenyl]pyrylium perchlo-

rate ꢀ17). A solution of diketone 16 (5.82 g, 11.0 mmol)

and triphenylcarbenium perchlorate (3.76 g, 11.0 mmol)

in glacial acetic acid (25 ml) was heated under reﬂux for

15 min. After cooling to room temperature, the pre-

cipitate formed was ﬁltered off, washed with diethyl

ether, recrystallized from glacial acetic acid or aceto-

nitrile, and dried with KOH in vacuo, to yield the

pyrylium salt 17 (3.42 g, 51%) as shiny, yellow, plate-

like crystals with m.p. 287°C (decomp.). IR (KBr):

ꢀeꢀcm^À1 1067 (ClO₄). ¹H NMR (CD₃COCD₃): ꢂ

(ppm) = 8.13 and 8.80 (AA BB, 4 H, 4-phenyl-H), 8.16

and 8.93 (AA BB, 8 H, 2,6-phenyl-H). ¹³C NMR

(CD₃COCD₃): ꢂ (ppm) = 119.7 (pyrylium-C-3), 124.5

(q, ¹J_CF= 272 Hz, two CF₃), 124.6 (q, ¹J_CF= 272 Hz, one

CF₃), 127.6, 131.4, 131.8, 133.6, 135.9 (q, ²J_CF= 32 Hz,

1

¹³C NMR (CDCl₃): ꢂ (ppm) = 123.7 (q, J_CF= 272 Hz,

3

CF₃), 125.9 (quat. phenol-C-2), 126.2 (q, J_CF= 3.6 Hz,

C=C–CF₃), 128.4 (phenyl-C), 129.6 (phenol-C-3), 131.0

2

(q, J_CF= 33 Hz, C–CF₃), 138.5 (phenyl-C), 141.5

(C–NO₂), 154.2 (C–OH). ¹⁹F NMR (CDCl₃):

ꢂ

(ppm) = À62.9 (s, CF₃). MS (FD): m/z (%) = 427 (100)

Copyright  2001 John Wiley & Sons, Ltd.

J. Phys. Org. Chem. 2001; 14: 737–751

NEW F-SUBSTITUTED SOLVATOCHROMIC BETAINE DYES

747

[M ]. C₂₀H₁₁F₆NO₃(427.3): calcd C 56.22, H 2.59, N

ꢀ`penta-CF₃-betaine'). To a stirred solution of perchlo-

rate 22 (0.96 g, 0.97 mmol) in dry dichloromethane

(40 ml) was added the granulated polymer base (diethyl-

aminomethyl)polystyrene (Fluka, 1.00 g, base equivalent

ca 3 mmol) and the suspension was stirred for 30 min at

room temperature. Then, the polymer base was ﬁltered

off, washed with dichloromethane and discarded. The

solvent from the combined ﬁltrates was distilled off and

the solid residue was dried with P₄O₁₀in vacuo, to yield

betaine dye 4 (0.71 g, 82%) as ﬁne green crystals which

melted, after a phase transition at 180–195°C, at 284°C.

UV–Vis (CH₃CN): l_max(log ꢁ) = 632 (3.09), 381 (3.48).

¹H NMR (CD₃COCD₃): ꢂ (ppm) = 7.52 (s, 2H, pheno-

late-3-H), 7.45 and 7.64 (AA BB, 8 H, phenyl-H), 7.86

and 7.93 (AA BB, 8 H, phenyl-H), 8.01 and 8.50 (AA

BB, 4 H, phenyl-H), 8.85 (s, 2 H, pyridinium-3-H). ¹³C

3.28; found C 56.30, H 2.18, N 3.14%.

4-Amino-2,6-di[4-ꢀtri¯uoromethyl)phenyl]phenol ꢀ21).

A suspension of a palladium catalyst (10% Pd on

charcoal; ca 200 mg) in a solution of nitrophenol 20

(4.04 g, 9.45 mmol) in ethanol (100 ml; 96%, v/v) was

reduced with dihydrogen at room temperature and normal

pressure until the necessary amount of H₂was absorbed.

Under nitrogen, the catalyst was ﬁltered off and the

solvent was distilled off in vacuo, to afford 21 (3.68 g,

98%) as yellow microcrystals with m.p. 158–162°C,

which turned reddish in air. Because of its sensitivity to

oxygen, 21 was immediately converted into the pyridi-

nium salt 22 without further detailed characterization. ¹H

NMR (CD₃COCD₃): ꢂ (ppm) = 2.13 (s, 2 H, NH₂), 6.74

(s, 2 H, phenol-3-H), 6.83 (s, 1 H, OH), 7.80 (AA BB, 4

H, phenyl-H).

1

NMR (CD₃COCD₃): ꢂ (ppm) = 124.8 (q, J_CF= 272 Hz,

1

two CF₃), 124.9 (q, J_CF= 272 Hz, one CF₃), 125.3 (q,

3

¹J_CF= 272 Hz, two CF₃), 125.8 (q, J_CF= 3.8 Hz, two

3

1-{3,5-Di[4-ꢀtri¯uoromethyl)phenyl]-4-hydroxyphe-

nyl}-2,4,6-tri[4-ꢀtri¯uoromethyl)phenyl]pyridinium per-

chlorate ꢀ22).

C=

C–CF₃), 126.2 (q, J_CF= 3.8 Hz, two C

=

C–CF₃),

3

127.3 (q, J_CF= 4.5 Hz, one C

late-C-3), 129.7 (q, J_CF= 32 Hz, two C–CF₃), 130.3,

=C–CF₃), 128.2 (pheno-

2

A

solution of freshly prepared

aminophenol 21 (3.75 g, 9.44 mmol), pyrylium salt 17

(4.82 g, 7.87 mmol), and water-free sodium acetate

(1.55 g, 18.9 mmol) in dry ethanol (95 ml) was heated

under reﬂux for 2.5 h. Then, at room temperature, the

blue solution was acidiﬁed (pH ꢁ 1) by addition of a few

drops of aqueous HClO₄(70%, w/w) and the product was

precipitated by addition of water. The precipitate formed

was ﬁltered off, washed acid free with water, and dried

with P₄O₁₀in vacuo. The product was recrystallized from

xylene, digested with diethyl ether at room temperature

for 2 h, and again dried with P₄O₁₀in vacuo, to afford

perchlorate 22 (6.91 g, 89%) as ﬁne colorless needles

which decomposed without melting at ca 300°C. IR

(KBr): ꢀe ꢀcm^À1 3559 (OH), 1067 (ClO₄). UV–Vis

130.4, 130.6, 130.8, 131.3 (pyridinium-C-3), 131.9,

2

132.3 (q, J_CF= 32 Hz, two C–CF₃), 133.7 (q,

²J_CF= 32 Hz, one C–CF₃), 138.3, 139.1, 142.1 (pheno-

late-C-2), 155.8 (phenolate-C-4), 156.5 (pyridinium-C-

2), 156.9 (C–O^À). ¹⁹F NMR (CD₃COCD₃):

ꢂ

(ppm) = À62.4 (s, 3 F, CF₃), À63.3 (s, 6 F, two CF₃),

À63.8 (s, 6 F, two CF₃). MS (FD): m/z (%) = 891 (100)

[M ]. C₄₆H₂₄F₁₅NO (891.7): calcd C 61.96, H 2.71, N

1.57, F 31.96; found C 56.79, H 2.30, N 1.51, F 29.44%.

Because of the high ﬂuorine content of 4, the value found

for carbon is too low.

Synthesis of betaine dye 5 5Scheme 4). 4-ꢀTrideca-

¯uorohex-1-yl)acetophenone ꢀ24). In a 250 ml three-

necked round-bottomed ﬂask with a thermometer and

reﬂux condenser, copper bronze (Aldrich, copper powder

99% for organic syntheses; 11.21 g, 1.76 mmol) was

dried by heating it under nitrogen. At room temperature, a

solution of 4-iodoacetophenone 23 (15.88 g, 64.5 mmol)

in water-free dimethyl sulfoxide (110 ml) was added and

the suspension was heated to 125–130°C. At this

1

(CH₃CN): l_max(log ꢁ) = 295 (4.61), 231 nm (4.63). H

NMR (CD₃COCD₃): ꢂ (ppm) = 7.67 (s, 2 H, phenol-3-H),

7.48 and 7.74 (AA BB, 8 H, phenyl-H), 7.90 and 7.97

(AA BB, 8 H, phenyl-H), 8.03 and 8.51 (AA BB, 4 H,

phenyl-H), 8.87 (s, 2 H, pyridinium-3-H). ¹³C NMR

1

(CD₃COCD₃): ꢂ (ppm) = 124.8 (q, J_CF= 272 Hz, two

1

CF₃), 124.9 (q, J_CF= 272 Hz, one CF₃), 125.2 (q,

3

¹J_CF= 272 Hz, two CF₃), 126.2, 127.3 (q, J_CF= 3.8 Hz,

temperature,

iodine-free

perﬂuoro-1-iodohexane

C

=

C–CF₃), 128.3 (phenol-C-3), 130.5, 130.6, 131.0,

(34.54 g, 77.4 mmol) was slowly added over a period of

1–1.5 h and heating was continued for 5 h. After cooling

to room temperature, the precipitate formed (copper

bronze and copper iodide) was ﬁltered off and washed

ﬁve times with diethyl ether. The combined ﬁltrates were

washed DMSO free with water and dried with MgSO₄.

Then, the solvent was distilled off and the residue was

puriﬁed by fractional distillation, to give ketone 24

(22.89 g, 81%) as a colourless liquid with b.p. 64–65°C/

0.008 Torr, which solidiﬁed on standing to colorless

crystals with m.p. 47–49°C (lit.^25,26b.p. 68°C/

0.039 Torr; m.p. 47–49°C). ¹H NMR (CDCl₃): ꢂ

(ppm) = 2.66 (s, 3 H, CH₃), 7.72 and 8.09 (AA BB, 4

2

132.0, 131.5 (pyridinium-C-3), 132.4 (q, J_CF= 32 Hz,

two C–CF₃), 132.5 (pyridinium-C-4), 133.7 (q,

²J_CF= 32 Hz, one C–CF₃), 135.2, 139.2, 141.2, (phenol-

C-2), 152.8 (phenol-C-4), 157.0 (pyridinium-C-2), 157.1

(C–OH). ¹⁹F NMR (CD₃COCD₃): ꢂ (ppm) = À62.2 (s, 6

F, two CF₃), À62.6 (s, 6 F, two CF₃), À62.7 (s, 3 F, CF₃).

MS (FD): m/z (%) = 892 (33) [M ÀClO₄], 513 (100).

C₄₆H₂₅ClF₁₅NO₅(992.1): calcd. C 55.69, H 2.54, N 1.41,

F 28.72; found C 55.56, H 2.57, N 1.38, F 28.54%.

4-{2,4,6-Tri[4-ꢀtri¯uoromethyl)phenyl]pyridinium-1-

yl}-2,6-di[4-ꢀtri¯uoromethyl)phenyl]phenolate

ꢀ4)

J. Phys. Org. Chem. 2001; 14: 737–751

¨

C. REICHARDT, M. ESCHNER AND G. SCHAFER

748

H, phenyl-H). ¹³C NMR (CDCl₃): ꢂ (ppm) = 26.8 (CH₃),

127.4 (t, ³J_CF= 6.5 Hz, phenyl-C-3), 128.5 (phenyl-C-2),

suspension of LiAlH₄(4.55 g, 120 mmol) in dry tetra-

hydrofuran (100 ml), placed in a 500 ml three-necked

round-bottomed ﬂask with a stirrer, dropping funnel, and

reﬂux condenser, a solution of ester 27 (23.41 g,

47.0 mmol) in tetrahydrofuran (60 ml) was slowly added

at ca 0°C with stirring. Stirring was continued for 30 min

and then the mixture was heated under reﬂux for 2 h.

After cooling to ca 0°C, the mixture was hydrolyzed by

addition of ice-cold water and then acidiﬁed (pH ꢁ 1) by

addition of dilute HCl. After addition of diethyl ether, the

organic and aqueous phase were separated and the

aqueous phase was extracted four times with diethyl

ether in a separating funnel. The combined ethereal

phases were washed with saturated aqueous NaCl

solution and dried with MgSO₄. The solvent was distilled

off, to afford crude 28 (19.62 g, ca 93%) as a yellow oil,

which partly solidiﬁed on standing at room temperature.

According to its ¹H NMR spectrum, the purity of 28 was

ca 95%, which was sufﬁcient for the next reaction step.

¹H NMR (CDCl₃): ꢂ (ppm) = 2.06 (s, 1 H, OH), 4.78 (s, 2

H, CH₂), 7.50 and 7.58 (AA BB, 4 H, phenyl-H).

2

133.1 (t, J_CF= 24 Hz, phenyl-C-4), 139.9 (phenyl-C-

1 = C–CO–CH₃), 197.1 (C=

O). ¹⁹F NMR (CDCl₃): ꢂ

4

(ppm) = À81.3 (t, J_FF= 10 Hz, 3 F, CF₃), À111.7 (t,

⁴J_FF= 10 Hz, 2 F, CF₂-1), À121.9 (broad m, 2 F, CF₂-2 or

CF₂-3), À122.3 (m, 2 F, CF₂-3 or CF₂-2), À123.3 (m, 2 F,

CF₂-4), À126.6 (m, 2 F, CF₂-5). For the C numbering of

the perﬂuorohexyl chain, see Scheme 4.

Ethyl 4-bromobenzoate ꢀ26). To a stirred suspension of

4-bromobenzoic acid 25 (50.00 g, 250 mmol) and

triethyloxonium tetraﬂuoroborate (49.02 g, 270 mmol)²⁷

in dry dichloromethane (300 ml) was added dropwise at

0°C ethyl diisopropylamine (32.15 g, 250 mmol) and

then stirring was continued for 24 h at room temperature.

In a separating funnel, the reaction mixture was extracted

twice with aqueous NaHCO₃solution (2 Â 150 ml), and

washed subsequently with water (150 ml), aqueous 2 M

HCl and again with water. After drying with MgSO₄, the

solvent was distilled off and the residue was puriﬁed by

fractional distillation, to afford the ester 26 (46.62 g,

81%) as a colorless liquid with b.p. 136°C/23 Torr (lit.⁴¹

4-ꢀTrideca¯uorohex-1-yl)benzaldehyde ꢀ29). To a stir-

red suspension of pyridinium ﬂuorochromate (12.83 g,

64.0 mmol)²⁸in dry dichloromethane (70 ml), placed in a

250 ml three-necked round-bottomed ﬂask with a stirrer

and reﬂux condenser, a solution of alcohol 28 (19.62 g,

43.7 mmol) in dry dichloromethane (20 ml) was added at

room temperature and stirring was continued for 6 h.

Then, to the reaction mixture an equal volume of diethyl

ether was added and the solution was percolated under

vacuum through a silica gel bed placed on a sintered glass

funnel. The silica gel bed was thoroughly extracted with

diethyl ether. All ﬁltrates were combined, the solvent was

distilled off, and the residue was puriﬁed by fractional

distillation with a packed column (30 cm), ﬁlled with

Wilson spirals, to afford the aldehyde 29 (12.94 g, 70%)

as a colorless liquid with b.p. 90°C/0.1 Torr, which

1

136.8°C/17 Torr). H NMR (CDCl₃): ꢂ (ppm) = 1.39 (q,

3

³J = 7.2 Hz, 3 H, CH₃), 4.38 (q, J = 7.2 Hz, 2 H, CH₂),

7.58 and 7.91 (AA BB, 4 H, phenyl-H).

Ethyl 4-ꢀTrideca¯uorohex-1-yl)benzoate ꢀ27). In a

250 ml three-necked round-bottomed ﬂask with a ther-

mometer and reﬂux condenser, copper bronze (Aldrich,

copper powder 99% for organic syntheses; 5.21 g,

82.0 mmol) was dried by heating it under nitrogen. At

room temperature, a solution of ester 26 (6.87 g,

30.0 mmol) in water-free dimethyl sulfoxide (50 ml)

was added and the suspension was heated to 125–135°C.

At this temperature, iodine-free perﬂuoro-1-iodohexane

(10.05 g, 36.0 mmol) was added dropwise over a period

of ca 1 h and heating was continued for 18 h. After

cooling to room temperature and addition of diethyl ether

(50 ml), the precipitate formed (copper bronze and

copper iodide) was ﬁltered off and washed ﬁve times

with diethyl ether. The combined ﬁltrates were washed

DMSO free with water and dried with MgSO₄. Then, the

solvent was distilled off and the solid residue was puriﬁed

by fractional distillation with a spinning band column

(50 cm), to yield the ester 27 (8.02 g, 57%) as a colorless

liquid with b.p. 92–100°C/2 Torr, which solidiﬁed on

standing to colorless crystals with m.p. 29–30°C (lit.²⁶

b.p. 80–81°C/0.13 Torr and m.p. 29–30°C). According

solidiﬁed to colorless crystals with m.p. 29–33°C. IR

1

(KBr): ꢀeꢀcm^À1 1711 (C

=

O). H NMR (CDCl₃): ꢂ

(ppm) = 7.79 and 8.04 (AA BB, 4 H, phenyl-H), 10.13 (s,

1 H, CHO). ¹³C NMR (CDCl₃): ꢂ (ppm) = 110–119

(several m of low intensity, perﬂuorohexyl-C), 127.6 (t,

³J_CF= 6.4 Hz, C

=

C–CF₂–), 129.5 (C

=C–CHO), 134.2

2

(t, J_CF= 24 Hz, C–CF₂–), 138.7 (C–CHO), 190.9

(CHO). ¹⁹F NMR (CDCl₃): ꢂ (ppm) = À81.3 (t,

⁴J_FF= 10 Hz, 3 F, CF₃), À111.8 (t, J_FF= 14 Hz, 2 F,

4

CF₂-1), À121.9 (m, 2 F, CF₂-2 or CF₂-3), À122.2 (m, 2 F,

CF₂-3 or CF₂-2), À123.3 (m, 2 F, CF₂-4), À126.7 (m, 2 F,

CF₂-5). For the C numbering of the perﬂuorohexyl chain,

1

to its H NMR spectrum, the purity of 27 was ca 94%,

still containing some starting material and side products,

see Scheme 4. MS (EI; 70 eV): m/z (%) = 424 (75) [M ],

which were removed during the subsequent reaction

423 (66) [M À1], 405 (20) [M ÀF], 357 (4) [M

1

3

steps. H NMR (CDCl₃): ꢂ (ppm) = 1.42 (t, J = 7.2 Hz,

3H, CH₃), 4.43 (q, ³J = 7.2 Hz, 2 H, CH₂), 7.68 and 8.19

(AA BB, 4 H, phenyl-H).

ÀCF₃], 305 (1) [M ÀC₂F₅], 238 (1) [M ÀC₃F₇], 205

(3) [M ÀC₄F₉], 155 (100) [M ÀC₅F₁₁], 127 (75)

[C₆H₅–CF₂], 105 (2) [M ÀC₆F₁₃], 77 (19) [C₆H₅], 50

(8) [CF₂]. C₁₃H₅F₁₃O (424.2): calcd C 36.81, H 1.19;

4-ꢀTrideca¯uorohex-1-yl)benzyl alcohol ꢀ28). To a

found C 36.96, H 1.05%.

J. Phys. Org. Chem. 2001; 14: 737–751

NEW F-SUBSTITUTED SOLVATOCHROMIC BETAINE DYES

749

1,3-Di[4-ꢀtrideca¯uorohex-1-yl)phenyl]-prop-2-en-1-

one ꢀ30). To a stirred solution of NaOH (1.02 g,

25.6 mmol) in water (20 ml) and ethanol (60 ml, 96%,

v/v) were added ketone 24 (8.76 g, 20.0 mmol) and

aldehyde 29 (8.48 g, 20.0 mmol). After stirring at room

temperature for 1 h, the precipitate formed was ﬁltered

off, washed with water, and dried with P₄O₁₀in vacuo, to

give chalcone 30 (16.35 g, ca 97%) as light-yellow

crystals, which were sufﬁciently pure for the next

reaction step. Recrystallization from 2-propanol yielded

[M ÀClO₄]. C₄₁H₁₄ClF₃₉O₅(1362.9): calcd C 36.13, H

1.04; found C 35.95, H 1.02%.

1-ꢀ3,5-Diphenyl-4-hydroxyphenyl)-2,4,6-tri[4-ꢀtrideca-

¯uorohex-1-yl)phenyl]pyridinium perchlorate ꢀ32). A

solution of freshly prepared 4-amino-2,6-diphenylphenol

(0.65 g, 2.49 mmol),^3a,19pyrylium salt 31 (2.79 g,

2.05 mmol), and water-free sodium acetate (0.42 g,

5.12 mmol) in dry ethanol (25 ml) was heated under

reﬂux for 2 h. At room temperature, the solution was

acidiﬁed (pH ꢁ 1) by addition of a few drops of HClO₄

(70%, w/w) and the product was precipitated by addition

of water. After standing for ca 12 h at room temperature,

the precipitate formed was ﬁltered off, washed acid free

with water, recrystallized from a small amount of 2-

propanol and dried with P₄O₁₀in vacuo, to afford

perchlorate 32 (2.94 g, 89%) as yellow needles with m.p.

138–140°C. IR (KBr): ꢀe ꢀcm^À1 1096 (CIO₄). UV–

analytically pure 30 as light-yellow crystals with m.p.

1

138–140°C. IR (KBr): ꢀe ꢀcm^À1 1688 (C

=

O). H

NMR (CDCl₃): ꢂ (ppm) = 7.58 (B part of AB system,

³J = 16 Hz, 1 H, CH–CO), 7.76 and 7.79 (AA BB, 4 H,

3

phenyl-H), 7.86 (A part of AB system, J = 16 Hz, 1 H,

CH=CH–CO), 7.67 and 8.14 (AA BB, 4 H, phenyl-H).

¹³C NMR (CDCl₃): ꢂ (ppm) = 123.9 (CH–CO), 127.6,

3

128.5, 128.7, 130.8 (t, J_CF= 49 Hz, C–C₆F₁₃), 132.9 (t,

³J_CF= 49 Hz, C–C₆F₁₃), 138.1, 140.8, 143.9 (CH

=

CH–

Vis (CH₃CN): l_max(1g ꢁ) = 295 nm (4.65). H NMR

1

CO), 189.2 (C

=

O). Because of their low intensity, the

(CDCl₃): ꢂ (ppm) = 7.16 (s, 2 H, phenolate-3-H), 5.57 (s,

1 H, OH), 7.01, 7.67, 7.73, and 7.95 (four m, phenyl-H),

8.08 (s, 2 H, pyridinium-3-H). ¹³C NMR (CD₃COCD₃): ꢂ

(ppm) = 127.7, 128.3 (phenolate-C-3), 128.7, 128.8,

129.2, 130.0, 130.4, 130.6, 131.4, 130.9 (t,

¹³C signals of the two perﬂuorohexyl groups are not seen

in the spectrum. ¹⁹F NMR (CDCl₃): ꢂ (ppm) = À81.2 (m,

6 F, two CF₃), À111.5 (m, 2 F), À111.6 (m, 2 F), À121.9

(m, 4 F), À122.3 (m, 4 F), À123.2 (m, 4 F), À126.6 (m, 4

F) for the CF₂groups. MS (FD): m/z (%) = 844 (100)

2

²J_CF= 34 Hz, two C–C₆F₁₃), 131.8 (t, J_CFnot measur-

[M ]. C₂₇H₁₀F₂₆O (844.3): calcd C 38.41, H 1.19; found

able, one C–C₆F₁₃), 137.8, 138.4, 139.5 (phenolate-C-2),

141.8 (phenolate-C-4), 152.6 (pyridinium-C-2), 156.8

(C–OH). Because of their low intensity, the ¹³C signals of

the three perﬂuorohexyl groups are not seen in the

spectrum. ¹⁹F NMR (CD₃COCD₃): ꢂ (ppm) = À81.2 (9 F,

three CF₃), À110.9 (6 F, CF₂-1), À121.6 (12 F, CF₂-2

and CF₂-3), À122.9 (6 F, CF₂-4), À126.3 (CF₂-5). For

the C numbering of the perﬂuoroalkyl chain, see Scheme

C 38.25, H 1.00%.

2,4,6-Tri[4-ꢀtrideca¯uorohex-1-yl)phenyl]pyrylium per-

chlorate ꢀ31). In a 100 ml three-necked round-bottomed

ﬂask with a stirrer, dropping funnel, and reﬂux con-

denser, a mixture of chalcone 30 (4.22 g, 5.00 mmol) and

ketone 24 (2.19 g, 5.00 mmol) was heated with stirring

until a homogeneous melt was formed (bath temperature

95–100°C). Then, aqueous HClO₄(70%, w/w; 1.15 g,

8.00 mmol) was slowly added dropwise and the mixture

was held at 100°C for 1 h. After 5–10 min, the product

already separated out from the hot, red reaction mixture.

After cooling to room temperature, diethyl ether (50 ml)

was added and the precipitate formed was ﬁltered off,

washed with diethyl ether, recrystallized from glacial

acetic acid, and dried with KOH in vacuo, to yield the

pyrylium salt 31 (1.36 g, 20%) as shiny orange crystals

with m.p. 226–229°C. IR (KBr): ꢀe ꢀcm^À1 1100

(ClO₄). ¹H NMR (CD₃COCD₃): ꢂ (ppm) = 8.17 and

8.87 (AA BB, 4 H, 4-phenyl-H), 8.21 and 9.01 (AA BB, 8

H, 2- and 6-phenyl-H), 9.61 (s, 2 H, pyrylium-2-H). ¹³C

NMR (CD₃COCD₃): ꢂ (ppm) = 129.2, 131.7, 133.9,

134.6, and 137.9 (phenyl-C), 167.4 (pyrylium-C-4),

171.8 (pyrylium-C-2). Because of their low intensity,

the ¹³C signals of the three perﬂuorohexyl groups are

not seen in the spectrum. ¹⁹F NMR (CD₃COCD₃): ꢂ

4. MS (FD): m/z (%) = 1507 (100) [M ÀClO₄], 1499

(21). C H ClF NO 0.5H O (1606.2 9.0 = 1615.2):

₅Á

59 27

39

2

calcd C 43.87, H 1.75, N 0.86; found C 43.86, H 1.84, N

0.90%.

2,6-Diphenyl-4-{2,4,6-[4-ꢀtrideca¯uorohex-1-yl)phe-

nyl]pyridinium-1-yl}phenolate ꢀ5) ꢀ`tris-C₆F₁₃-betaine').

To a solution of perchlorate 32 (2.85 g, 1.76 mmol)

in dry methanol (45 ml) sodium methanolate (0.24 g,

4.44 mmol) was added and the dark solution was heated

under reﬂux for 5 min. The cold solution was then poured

into aqueous NaOH (10%, w/w; 150 ml). After standing

for ca 12 h at room temperature, the precipitate formed

was ﬁltered off, washed with water, dried with P₄O₁₀in

vacuo, recrystallized from 2-propanol, and dried again, to

yield betaine dye 5 (2.00 g, 74%) as ﬁne dark-green

crystals with m.p. 237–240°C (decomp.). UV–Vis

(CH₃CN): l_max(log ꢁ) = 691 (3.87), 380 (4.06), 290 nm

1

(4.42). H NMR (CD₃COCD₃): ꢂ (ppm) = 6.81 (s, 2 H,

4

(ppm) = À81.2 (t, J_FF= 9 Hz, three CF₃), À111.1 (m, 6

phenolate-3-H), 7.05 and 7.37 (AA BB, 10 H, 2,6-

diphenylphenolate-H), 7.87 and 7.96 (AA BB, 8 H, 2,6-

diphenylpyridinium-H), 7.99 and 8.59 (AA BB, 4 H, 4-

F, CF₂-1), À121.4 (m, 6 F, CF₂-2 or CF₂-3), À121.6 (m, 6

F, CF₂-3 or CF₂-2), À122.9 (m, 6 F, CF₂-4), À126.3 (m, 6

F, CF₂-5). For the C numbering of the perﬂuorohexyl

chain, see Scheme 4. MS (FD): m/z (%) = 1263 (100)

phenylpyridinium-H), 8.81 (s, 2 H, pyridinium-3-H). ¹³

C

NMR (CD₃COCD₃): ꢂ (ppm) = 125.4, 127.4, 127.8,

J. Phys. Org. Chem. 2001; 14: 737–751

¨

C. REICHARDT, M. ESCHNER AND G. SCHAFER

750

(2nd edn). VCH: Weinheim, 1988, chapt. 7, 339–405; (b) Buncel

E, Rajagopal S. Acc. Chem. Res. 1990; 23: 226–231; (c) Laurence

C. In Similarity Models in Organic Chemistry, Biochemistry, and

Related Fields, Zalewski RI, Krygowski TM, Shorter J (eds).

Elsevier: Amsterdam, 1991, chapt. 5, 231–281; (d) Abboud J-LM,

Notario R. Pure Appl. Chem. 1999; 71: 645–718; (e) Catala´n J. In

Handbook of Solvents, Wypych G (ed). ChemTec Publishing:

Toronto and William Andrew Publishing: Norwich, NY, 2001,

chapt. 10.3, 583–616.

128.6 (phenolate-C-3), 128.7, 129.5, 129.7, 129.9, 130.1,

131.1, 131.3 (pyridinium-C-3), 139.4, 140.0, 142.8

(phenolate-C-2), 152.6 (phenolate-C-4), 155.5 (pyridi-

nium-C-2), 171.2 (C–O^À). Because of their low intensity,

the ¹³C signals of the three perﬂuoroalkyl groups are not

seen in the spectrum. ¹⁹F NMR (CD₃COCD₃): ꢂ

(ppm) = À81.2 (9 F, three CF₃), À110.9 (6 F, CF₂-1),

À121.6 (12 F, CF₂-2 and CF₂-3), À122.9 (6 F, CF₂-4),

À126.3 (6 F, CF₂-5). For the C numbering of the

11. Reichardt C, Asharin-Fard S, Blum A, Eschner M, Mehranpour A-

M, Milart P, Niem Th, Scha¨fer G, Wilk M. Pure Appl. Chem. 1993;

65: 2593–2601.

perﬂuoroalkyl chain, see Scheme 4. MS (FD): m/z

12. (a) Chapman NB, Shorter J (eds). Advances in Linear Free Energy

Relationships. Plenum Press: London, 1972; (b) Chapman NB,

Shorter J (eds). Correlation Analysis in Chemistry – Recent

Advances. Plenum Press: New York, 1978; (c) Shorter J.

Correlation Analysis of Organic Reactivity. Research Studies

Press: Chichester, 1982; (d) Exner O. Correlation Analysis of

Chemical Data. Plenum Press: New York and SNTL, Prague,

1988.

(%) = 1505 (100) [M ]. C H F NO H O (1505.8

Á

59 26 39

2

18.0 = 1523.8): calcd C 46.50, H 1.85, N 0.92; found C

46.99, H 2.17, N 0.95%.

Acknowledgements

13. Laurence C, Nicolet P, Reichardt C. Bull. Soc. Chim. Fr. 1987;

125–130.

14. Eberhardt R, Lo¨bbecke S, Neidhart B, Reichardt C. Liebigs Ann./

Rec. 1997; 1195–1199.

15. Reichardt C, Lo¨bbecke S, Mehranpour A-M, Scha¨fer G. Can. J.

Chem. 1998; 76: 686–694.

16. (a) Cornils B. Angew. Chem. 1997; 109: 2147–2149; Angew.

Chem., Int. Ed. Engl. 1997; 36: 2057–2059; (b) Horva´th IT. Acc.

Chem. Res. 1998; 31: 641–650; (c) Betzemeier B, Knochel P. Top.

Curr. Chem. 1999; 206: 61–78; (d) Enders A, Maas G. Chem.

Unserer Zeit 2000; 34: 382–393.

17. Kessler MA, Wolfbeis OS. Chem. Phys. Lipids 1989; 50: 51–56;

Chem. Abstr. 1989; 111: 59537u.

Financial support of this work by the Deutsche

Forschungsgemeinschaft, Bonn, and the Fonds der

Chemischen Industrie, Frankfurt/Main, is gratefully

acknowledged.

REFERENCES

1. Reichardt C, Che D, Heckenkemper G, Scha¨fer G. Eur. J. Org.

Chem. 2001; 2343–2361.

18. Drummond CJ, Grieser F, Healy TW. Faraday Discuss. Chem.

Soc. 1986; 81: 95–106; Chem. Abstr. 1987; 106: 126332k.

19. (a) Johnson BP, Gabrielsen B, Matulenko M, Dorsey JG, Reichardt

C. Anal. Lett. 1986; 19: 939–962; (b) Kessler MA, Wolfbeis OS.

Synthesis 1988; 635–636; (c) Rezende MC, Radetski CM. Quim.

Nova 1988; 11: 353–354; Chem. Abstr. 1989; 111: 8876w; (d)

Osterby BR, McKelvey RD. J. Chem. Educ. 1996; 73: 260–261,

737.

2. Eschner M. PhD Thesis, Philipps University, Marburg, 1991.

3. (a) Dimroth K, Reichardt C, Siepmann Th, Bohlmann F. Justus

Liebigs Ann. Chem. 1963; 661: 1–37; (b) Reichardt C, Harbusch-

Go¨rnert E. Justus Liebigs Ann. Chem. 1983; 721–743; (c)

Reichardt C, Scha¨fer G. Liebigs Ann. Chem. 1995; 1579–1582.

4. (a) Reichardt C. Chem. Soc. Rev. 1992; 21: 147–153; (b) Reichardt

C. Chem. Rev. 1994; 94: 2319–2358; (c) Reichardt C. Chem. Intell.

1997; 3: 5.

20. Filler R, Beaucaire VD, Kang HH. J. Org. Chem. 1975; 40: 935–

939.

5. (a) Mu¨ller P. Glossary of Terms used in Physical Organic

Chemistry–IUPAC Recommendations 1994. Pure Appl. Chem.

1994; 66: 1077–1184, particularly p. 1151; (b) Reichardt C. Nachr.

Chem. Tech. Lab. 1997; 45: 759–763; (c) Reichardt C. Visn.

Khark. Univ. 1999; 437, Issue 3(26): 9–16; Chem. Abstr. 2000;

132: 180091f.

6. (a) Dimroth K, Reichardt C, Schweig A. Justus Liebigs Ann. Chem.

1963; 669: 95–105; (b) Zalewski R, Adamczewska I, Reichardt C.

J. Chem. Res. (S) 1990; 280–281; J. Chem. Res. (M) 1990; 2157–

2176; (c) Bublitz GU, Boxer SG. J. Am. Chem. Soc. 1998; 120:

3988–3992; (d) Lagalante AF, Spadi M, Bruno TJ. J. Chem. Eng.

Data 2000; 45: 382–385.

21. Vlasov VM. Izv. Sib. Otd. Akad. Nauk SSSR, Ser. Khim. Nauk

1971; 96–103; Chem. Abstr. 1972; 76: 140411d.

22. (a) Balaban AT, Schroth W, Fischer G. Adv. Heterocycl. Chem.

1969; 10: 241–326; (b) Balaban AT, Dinculescu A, Dorofeenko

GN, Fischer GW, Koblik AV, Mezheritskii VV, Schroth W. Adv.

Heterocycl. Chem., Suppl. 2 1982.

23. (a) Nesmeyanov AN, Zol’nikova GP, Babakhina GM, Kritskaya II,

Yakobson GG. Zh. Obshch. Khim. 1973; 43: 2007–2012; J. Gen.

Chem. USSR 1973; 43: 1993–1997; Chem. Abstr. 1974; 80:

15042r; (b) Yoshisato E, Tsutsumi S. J. Org. Chem. 1968; 33:

869–871.

24. (a) Fanta PE. Org. Synth., Coll. Vol. 1963; 4: 844–845; Org.

Synth., Coll. 1973; 5: 1004; (b) Fanta PE, Stein RA. Chem. Rev.

1960; 60: 261–266.

25. McLoughlin VCR, Thrower J. Tetrahedron 1969; 25: 5921–5940.

26. Chen GJ, Tamborski C. J. Fluorine Chem. 1989; 43: 207–228.

27. Meerwein H. Org. Synth., Coll. Vol. 1973; 5: 1080–1082.

28. Bhattacharjee MN, Chaudhari MK, Dasgupta HS, Roy N,

Khathing DT. Synthesis 1982; 588–590.

29. (a) Jano I. J. Chim. Phys. 1992; 89: 1951–1971; (b) Rauhut G,

Clark T, Steinke Th. J. Am. Chem. Soc. 1993; 115: 9174–9181; (c)

Bica de Alencastro R, Da Motta Neto JD, Zerner MC. Int. J.

Quantum Chem., Quantum Chem. Symp. 1994; 28: 361–377;

Chem. Abstr. 1995; 122: 83696t; (d) Perng B-C, Newton MD,

Raineri FO, Friedman HL. J. Chem. Phys. 1996; 104: 7177–7204;

(e) Lipinsky J, Bartkowiak W. Chem. Phys. 1999; 245: 263–276;

(f) Fabian J, Rosquete GA, Montero-Cabrera LA. J. Mol. Struct.

(THEOCHEM) 1999; 469: 163–176; (g) Mente SR, Maroncelli M.

J. Phys. Chem. B 1999; 103: 7704–7719; (h) Lobaugh J, Rossky

PJ. J. Phys. Chem. A 2000; 104: 899–907; (i) Hogiu S, Dreyer J,

Pfeiffer M, Brzezinka K-W, Werncke W. J. Raman Spectrosc.

7. (a) Tamura K, Imoto T. Bull. Chem. Soc. Jpn. 1975; 48: 369–374;

(b) Hammack WS, Hendrickson DN, Drickamer HG. J. Phys.

Chem. 1989; 93: 3483–3487.

8. (a) Reichardt C, Asharin-Fard S, Scha¨fer G. Chem. Ber. 1993; 126:

143–147; (b) Hollmann G, Vo¨gtle F. Chem. Ber. 1984; 117: 1355–

1363; (c) Koppel IA, Koppel JB. Org. React. (Tartu) 1984; 21: 98–

123; Chem. Abstr. 1985; 103: 37044p; (d) Rezende MC.

Tetrahedron 1988; 44: 3513–3522; (e) Pocker Y, Ciula JC. J.

Am. Chem. Soc. 1989; 111: 4728–4735; (f) Gageiro V, Aillon M,

Rezende MC. J. Chem. Soc., Faraday Trans. 1992; 88: 201–204;

(g) Binder DA, Kreevoy MM. J. Phys. Chem. 1994; 98: 10008–

10016; (h) Lavallee RJ, Zimmt MB. J. Phys. Chem. 1994; 98:

4254–4260; (i) Ohno H, Kawanabe H. Polym. Adv. Technol. 1996;

7: 754–758; (j) Huddleston JG, Willauer HD, Rogers RD. J.

Chromatogr. B 2000; 743: 137–149; (k) Dolman M, Mason AJ,

Samankumara Sandanayake KRA, Sheridan A, Sholl AF, Suther-

land IO. Analyst 1996; 121: 1775–1778.

9. Reichardt C, Blum A, Harms K, Scha¨fer G. Liebigs Ann./Recl.

1997; 707–720.

10. (a) Reichardt C. Solvents and Solvent Effects in Organic Chemistry

J. Phys. Org. Chem. 2001; 14: 737–751

NEW F-SUBSTITUTED SOLVATOCHROMIC BETAINE DYES

751

2000; 31: 797–803; (j) Ishida T, Rossky PJ. J. Phys. Chem. A 2001;

105: 558–565.

Macromolecules 1990; 23: 4557–4564; (b) Hubert C, Fichou D,

Valat P, Garnier F, Villeret B. Polymer 1995; 36: 2663–2666;

Hubert C, Fichou D, Garnier F. Adv. Mater. 1995; 7: 914–917;

(c) Ohno H, Kawanabe H. Polym. Adv. Technol. 1996; 7: 754–

758; (d) Imai Y, Chujo Y. Macromolecules 2000; 33: 3059–3064;

(e) Richter-Egger DL, Li H, Tucker SA. Appl. Spectrosc. 2000; 54:

1151–1156.

30. (a) Serjeant FP, Dempsey B. Ionization Constants of Organic

Acids in Aqueous Solution. IUPAC Chemical Data Series No. 23,

Entry No. 2161. Pergamon Press: Oxford, 1979; 48; (b) Rochester

CM. In The Chemistry of the Hydroxyl Group. Part 1, Patai S (ed).

Interscience: London, 1971; chapt. 7, 327–392 (particularly Table

17 on p. 374).

31. (a) Spange S, Lauterbach M, Gyra A-K, Reichardt C. Liebigs Ann.

Chem. 1991; 323–329; (b) Hormadaly J, Marcus Y. J. Phys. Chem.

1979; 83: 2843–2848.

32. Hesse K, Hu¨nig S. Liebigs Ann. Chem. 1985; 715–739, particularly

p. 723.

33. Kosower EM. J. Am. Chem. Soc. 1958; 80: 3253–3260, 3261–

3267, 3267–3270.

37. (a) Spange S, Vilsmeier E, Zimmermann Y. J. Phys. Chem. B

2000; 104: 6417–6428; (b) Fischer K, Spange S. Macromol. Chem.

Phys. 2000; 201: 1922–1929; (c) Spange S, Vilsmeier E, Fischer

K, Reuter A, Prause S, Zimmermann Y, Schmidt Ch. Macromol.

Rapid. Commun. 2000; 21: 643–659; (d) Spange S, Schmidt Chr,

Kricheldorf HR. Langmuir 2001; 17: 856–865.

38. (a) Perrin DD, Armarego WLF. Puriﬁcation of Laboratory

Chemicals (3rd ed). Pergamon Press: Oxford, 1988; (b) Becker

HGO, Beckert R, Domschke G, Fangha¨nel E, Habicher WD, Metz,

P, Pavel D, Schwetlick K. Organikum–Organisch-chemisches

Grundpraktikum (21st edn). Wiley-VCH: Weinheim, 2001; chapt.

F, 741–762.

34. Grifﬁths TR, Pugh DC. J. Solution Chem. 1976; 8: 247–258;

Coord. Chem. Rev. 1979; 29: 129–211.

35. (a) Michels JJ, Dorsey JG. Langmuir 1990; 6: 414–419; (b) Rutan

SC, Harris JM. J. Chromatogr. A 1993; 656: 197–215; (c)

Macquarrie DJ, Tavener SJ, Gray GW, Heath PA, Rafelt JS,

Saulzet SI, Hardy JJE, Clark JH, Sutra P, Brunel D, di Renzo F,

Fajula F. New J. Chem. 1999; 23: 725–731; (d) Reinheimer A, van

Eldik R, Kisch H. J. Phys. Chem. B 2000; 104: 1014–1024.

36. (a) Paley MS, McGill RA, Howard SC, Wallace SE, Harris JM.

39. Hass HB, Bender ML. J. Am. Chem. Soc. 1949; 71: 1767–1769.

40. Pascal RA, McMillan WD, Van Engen D, Eason RG. J. Am. Chem.

Soc. 1987; 109: 4660–4665.

41. Raber DJ, Gariano P. Tetrahedron Lett. 1971; 4741–4744.

J. Phys. Org. Chem. 2001; 14: 737–751

Article Doi

Syntheses and UV-visible spectroscopic properties of new 'fluorophilic' fluorine-and perfluoroalkyl-substituted solvatochromic pyridinium N-phenolate betaine dyes

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