Red organic light-emitting radical adducts of carbazole and tris(2,4,6-trichlorotriphenyl)methyl radical that exhibit high thermal stability and electrochemical amphotericity

Article abstract of DOI:10.1021/jo0708846

(Chemical Equation Presented) Synthesis and characterization of new carbazolyl derivatives with a pendant stable radical of the TTM (tris-2,4,6-trichlorophenylmethyl radical) series are reported. The EPR spectra, electrochemical properties, absorption spe

Full text of DOI:10.1021/jo0708846

Red Organic Light-Emitting Radical Adducts of Carbazole and
Tris(2,4,6-trichlorotriphenyl)methyl Radical That Exhibit High
Thermal Stability and Electrochemical Amphotericity
Dolores Velasco,† Sonia Castellanos,‡ Marc Lo´pez,‡ Francisco Lo´pez-Calahorra,†
Enric Brillas,§ and Luis Julia´*,‡
Departament de Qu´ımica Orga`nica, Institut de Nanocie`ncies I Nanotecnologia, UniVersitat de Barcelona,
Mart´ı i Franque`s 1-11, 08028 Barcelona, Spain, Departament de Qu´ımica Orga`nica Biolo`gica, Institut
d’InVestigacions Qu´ımiques i Ambientals (CSIC), Jordi Girona 18-26, 08034 Barcelona, Spain,
and Departament de Qu´ımica F´ısica, UniVersitat de Barcelona, Mart´ı i Franque`s 1-11,
08028 Barcelona, Spain
ljbmoh@cid.csic.es
ReceiVed April 27, 2007
Synthesis and characterization of new carbazolyl derivatives with a pendant stable radical of the TTM
(tris-2,4,6-trichlorophenylmethyl radical) series are reported. The EPR spectra, electrochemical properties,
absorption spectra, and luminescent properties of these radical adducts have been studied. All of them
show electrochemical amphotericity being reduced and oxidized to their corresponding stable charged
species. The luminescence properties of them cover the red spectral band of the emission. The luminescence
of the electron-rich carbazole adducts shows the donor-acceptor nature of the excited state. On the
other hand, the EPR parameters of these radical adducts show an imperceptible variation with the
substituents in the carbazole.
Introduction
properties. They exhibit relatively intense luminescence and high
photoconductivities and undergo reversible oxidation processes
making them suitable as hole carriers.2 Consequently, carbazoles
are widely used as building blocks for potential organic
semiconductors.3
In the field of organic light-emitting diodes (OLED), carba-
zoles are used as the materials for hole-transporting and light-
emitting layers.4,5 Many carbazoles have a sufficiently high
triplet energy to host red as full-color triplet emitters.6 In
Carbazole is a heterocycle with the nitrogen atom singly
bonded to carbon atoms, and the low-lying n f π* transitions
in the electronic spectrum involving the nonbonding electrons
on nitrogen have properties similar to those of π f π*
transitions. This is why carbazole is a fundamental chromophore
that gives an efficient emission at λ ∼340 nm in dilute
solutions.1 The synthesis and applications of carbazole deriva-
tives have been a source of great interest for chemists and
materials scientists due to their intrinsic photophysical and redox
(2) Grazulevicius, J. V.; Strohriegl, P.; Pielichowski, J.; Pielichowski,
K. Prog. Polym. Sci. 2003, 28, 1297. Parimal, K.; Justin Thomas, K. R.;
Jiann, T. L.; Tao, Y. T.; Chien, C. H. AdV. Funct. Mater. 2003, 13, 445-
452. Akira, B.; Ken, O.; Wolfgang, K.; Rigoberto, C. A. J. Phys. Chem. B
2004, 108, 18949-18955.
(3) Wakim, S.; Bouchard, J.; Simard, M.; Drolet, N.; Tao, Y.; Leclerc,
M. Chem. Mater. 2004, 16, 4386-4388. Wakim, S.; Bouchard, J.; Bouchard,
J.; Blouin, N.; Michaud, A.; Leclerc, M. Org. Lett. 2004, 6, 3413-3416.
Martin, S.; Klaus, K.; Doris, H.; Peter, S.; Sepas, S.; Dago, D. L. Chem.
Mater. 2005, 17, 3031-3039. Nicolas, D.; Jean, F. M.; Nicolas, L.; Salem,
W.; Ye, T.; Mario, L. AdV. Funct. Mater. 2005, 15, 1671-1682. Morin, J.
F.; Leclerc, M.; Ades, D.; Siove, A. Macromol. Rapid Commun. 2005, 26,
761-764.
† Departament de Qu´ımica Orga`nica, Institut de Nanocie´ncies i Nanotecno-
logia, Universitat de Barcelona.
‡ Institut d’Investgacions Qu´ımiques i Ambientals (CSIC).
§ Departament de Qu´ımica F´ısica, Universitat de Barcelona.
(1) Berlman, I. B. In Handbook of Fluorescence Spectra of Aromatic
Molecules; Academic Press: New York, 1971; p 205. Mastrangelo, J. C.;
Conger, B. M.; Chen, S. H.; Bashir- Hashemi, A. Chem. Mater. 1997, 9,
227-232. Conger, B. M.; Katsis, D.; Mastrangelo, J. C.; Chen, S. H. J.
Phys. Chem. A 1998, 102, 9213-9218. Castex, M. C.; Olivero, C.; Pichler,
G.; Ades, D.; Cloutet, E.; Siove, A. Synth. Met. 2001, 122, 59-61.
10.1021/jo0708846 CCC: $37.00 © 2007 American Chemical Society
Published on Web 09/07/2007
J. Org. Chem. 2007, 72, 7523-7532
7523

Velasco et al.
addition, the carbazole ring is easily functionalized and co-
valently linked to other molecules.7,8 However, the poor
nucleophilic assistance of the nonbonding electron pair on the
nitrogen has made difficult its incorporation into aromatic
systems by classical methods, requiring severe reaction condi-
tions. Several synthetic strategies to obtain N-aryl derivatives
of carbazole by using Cu/bronze9 or palladium catalyst10 have
been published. Thus, different N-arylcarbazoles have been
prepared from electron-rich and electron-poor halobenzenes as
precursors, mainly bromo- and iodobenzenes. This is an easy
and direct way to successfully couple carbazole into polymers
such as poly(p-bromostyrene).11 The incorporation of carbazole
in the main chain12 or as a pendant group in the framework of
many polymers13 can greatly improve the photoconductivities
and hole transporting properties of them. Finally, another
important property of carbazole derivatives for technological
applications is their high thermal and photochemical stabilities.
Despite the huge amount of work already carried out with
carbazoles, more research efforts are needed to design and
synthesize new compounds with novel and improved properties
to meet all the demands that applications require. Recently, we
have reported the synthesis and properties of a new carbazole
derivative, the (4-N-carbazolyl-2,6-dichlorophenyl)bis(2,4,6-
trichlorophenyl)methyl radical (1•), resulting from the coupling
of the N-H-carbazole to the stable tris(2,4,6-trichlorophenyl)-
methyl (TTM) radical. This new paramagnetic adduct has
interesting electrochemical and luminescent properties and high
thermal stability.14 As far as we know, this is the third example
of a stable radical anchored to carbazole. The first two reported
examples refer to the preparation and characterization of
N-picryl-9-aminocarbazolyl radical15 and a diphenylpicryl-type
diradical of a carbazole dimer.16 Radicals of the series of TTM
are a kind of organic carbon-centered free radicals showing great
stability mainly due to steric hindrance of six chlorine atoms
around the trivalent carbon.17,18 All of these radicals are
completely disassociated and very stable either in solid or in
solution. Their inefficiency to abstract H-atoms from hydrogen-
labile species is accounted for by steric hindrance, and therefore
they are inoperatives in these processes. However, they are very
sensitive to electron-transfer reactions, being easily reduced to
carbanions with stabilities comparable to their precursors in the
presence of electron donor species, so that their electrochemical
behavior shows reversible reduction processes.
(4) Adamovich, V. I.; Cordero, S. R.; Djurovich, P. I.; Tamayo, A.;
Thompson, M. E.; D’Andrade, B. W.; Forrest, S. R. Org. Electron. 2003,
4, 77-87. van Dijken, A.; Bastiaansen, J. J. A. M.; Kiggen, N. M. M.;
Langeveld, B. M. W.; Rothe, C.; Monkman, A.; Bach, I.; Sto¨ssel, P.;
Brunner, K. J. Am. Chem. Soc. 2004, 126, 7718-7727. Morin, J. F.; Drolet,
N.; Tao, Y.; Leclerc, M. Chem. Mater. 2004, 16, 4619-4626. Justin
Thomas, K. R.; Velusamy, M.; Lin, J. T.; Tao, Y. T.; Chuen, C. H. AdV.
Funct. Mater. 2004, 14, 387-392. Brunner, K.; van Dijken, A. V.; Borner,
H.; Bastiaansen, J. J. A. M.; Kiggen, N. M. M.; Langeveld, B. M. W. J.
Am. Chem. Soc. 2004, 126, 6035-6042.
(5) Morin, J. F.; Leclerc, M. Macromolecules 2002, 35, 8413-8417.
(6) Gruner, J.; Wittmann, H. F.; Hamer, P. J.; Friend, R. H.; Huber, J.;
Scherf, U.; Mullen, K.; Moratti, S, C.; Holmes, A. B. Synth. Met 1994, 67,
181-185. Uekawa, M.; Miyamoto, Y.; Ikeda, H.; Kaifu, K.; Ichi, T.;
Nakaya, T. Thin Sol. Fims 1999, 352, 185-188. Park, J. W.; Lee, J. H.;
Lee, H. S.; Kang, D. Y.; Kim, T. W. Thin Sol. Films 2000, 363, 90-93.
Ahan, K. W.; Liu, Y. Q.; Yu, G.; Wu, X.; Zhu, D. B.; Sun, R. G.; Wang,
D. K.; Epstein, A. J. J. Mater. Chem. 2001, 11, 1606-1611. Walsh, C. J.;
Sooksimuang, T.; Mandal, B. K. J. Porph. Phthal. 2001, 5, 803-805. Ko,
C. W.; Tao, Y. T.; Lin, J. T.; Thomas, K. R. J. Chem. Mater. 2002, 14,
357-361. Thomas, K. R. J.; Lin, J. T.; Tao, Y. T.; Chuen, C. H. J. Mater.
Chem. 2002, 12, 3516-3522. Lee, J. H.; Woo, H. S.; Kim, T. W.; Park, J.
W. Opt. Mater. 2003, 21, 225-229. Das, R. R.; Lee, C. L.; Noh, Y. Y.;
Kim, J. J. Opt. Mater. 2003, 21, 143-146. Kundu, P.; Thomas, K. R. J.;
Lin, J. T.; Tao, Y. Y.; Chien, C. H. AdV. Funct. Mater. 2003, 13, 445-
452. Suzuki, M.; Tokito, S.; Kamachi, M.; Shirane, K.; Sato, F. J.
Photopolym. Sci. Tech. 2003, 16, 309-314. Anni, M.; Manna, L.; Cingolani,
R.; Valerini, D.; Creti, A.; Lomascolo, M. App. Phys. Lett. 2004, 85, 4169-
4171. Woo, H. S.; Cho, S.; Kwon, T. W.; Park, D. K.; Kim, Y. B.; Czerw,
R.; Carroll, D. L.; Park, J. W. J. Korean Phys. Soc. 2005, 46, 981-984.
Li, K. Z.; Zhang, Y.; Yang, R. Q.; Huang, J.; Yang, W.; Cao, Y. J. Polym.
Sci. Part A Polym. Chem. 2005, 43, 2325-2336.
(7) Zhang, Z. B.; Fujiki, M.; Tang, H. Z.; Motonaga, M.; Torimitsu, K.
Macromolecules 2002, 35, 1988-1990. Brizius, G.; Kroth, S.; Bunz, U.
H. F. Macromolecules 2002, 35, 5317-5319. Paik, K. L.; Baek, N. S.;
Kim, H. K.; Lee, J-H.; Lee, Y. Macromolecules 2002, 35, 6782. Bouchard,
J.; Belletele, M.; Durocher, G.; Leclerc, M. Macromolecules 2003, 36,
4624-4630. Sanda, F.; Kawaguchi, T.; Masuda, T.; Kobayashi, N.
Macromolecules 2003, 36, 2224-2229. Kim, K.; Hong, Y. R.; Lee, S. W.;
Jin, J. I.; Park, Y.; Sohn, B. H.; Kim, W. H.; Park, J. K. J. Mater. Chem.
2001, 11, 3023-3030.
(8) D´ıaz, J. L.; Dobarro, A.; Villacampa, B.; Velasco, D. Chem. Mater.
2001, 13, 2528-2536. D´ıaz, J. L.; Villacampa, B.; Lo´pez-Calahorra, F.;
Velasco, D. Chem. Mater. 2002, 14, 2240-2251.
(9) Martinez-Palau, M.; Perea, E.; Lo´pez-Calahorra, F.; Velasco, D. Lett.
Org. Chem. 2004, 1, 231-237.
(10) Mann, G.; Hartwig, J. F.; Driver, M. S.; Ferna´ndez-Rivas, C. J.
Am. Chem. Soc. 1998, 120, 827-828. Watanabe, M.; Nishiyama, M.;
Yamamoto, T.; Koie, Y. Tetrahedron Lett. 2000, 41, 481-483.
(11) Kanbara, T.; Yokokawa, Y.; Hasegawa, K. J. Polym. Sci. Part A:
Polym. Chem. 2000, 38, 28-34.
(12) Zhang, Y.; Wada, T.; Sasabe, H. J. Polym. Sci. Part A: Polym.
Chem. 1996, 34, 2289-2298. Wang, Q.; Gharvi, A.; Li, W.; Yu, L. Polym.
Prepr. (Am. Chem. Soc. DiV. Polym. Chem.) 1997, 38, 516. Morin, J. F.;
Leclerc, M. Macromolecules 2001, 34, 4680-4682. Huang, J.; Niu, Y.;
Yang, W.; Mo, Y.; Yuan, M.; Cao, Y. Macromolecules 2002, 35, 6080-
6082. Jiang, J.; Jiang, C.; Yang, W.; Zhen, H.; Hung, F.; Cao, Y.
Macromolecules 2005, 38, 4072-4080.
Nitroxide radicals are known to be excellent fluorescent
quenchers of aromatic hydrocarbons, presumably by an electron-
(13) Gratt, J.; Cohen, R. E. Macromolecules 1997, 30, 3137-3140.
Mustonen, I.; Hukka, T.; Pakkanen, T. Macromol. Rapid Commun. 2000,
21, 1286-1290. Hwang, J.; Sohn, J.; Park, S. Y. Macromolecules 2003,
36, 7970-7976. Grazulevicius, J. V.; Strohriegl, P.; Pielichowski, J.;
Pielichowski, K. Prog. Polym. Sci. 2003, 28, 1297-1353 and references
cited therein. Hsiao, S. H.; Chen, C. W.; Liou, G. S. J. Polym. Sci. Part A:
Polym. Chem. 2004, 42, 3302-3313. Chen, Z.; Liu, Y.; Zhang, C.; Bai, F.
J. Appl. Polym. Sci. 2004, 92, 2777. Liang, F.; Kurata, T.; Nishide, H.;
Kido, J. J. Polym. Sci. Part A Polim. Chem. 2005, 43, 5765-5773.
(14) Gamero, V.; Velasco, D.; Latorre, S.; Lo´pez-Calahorra, F.; Brillas,
E.; Julia´, L. Tetrahedron Lett. 2006, 47, 2305-2309.
(15) Kikuchi, C.; Cohen, V. W. Phys. ReV. 1954, 93, 394-399. Jarrett,
H. S. J. Chem. Phys. 1953, 21, 761. Lord, N. W.; Blinder, S. M. J. Chem.
Phys. 1961, 34, 1693-1708. Makino, H.; Nishiguchi, H.; Deguchi, Y.;
Takaki, H. Tetrahedron Lett. 1968, 2267-2269.
(16) Kozaki, M.; Okada, K. Synth. Met. 2001, 119, 177-178.
(17) Armet, O.; Veciana, J.; Rovira, C.; Riera, J.; Castan˜er, J.; Molins,
E.; Rius, J.; Miravitlles, C.; Olivella, S.; Brichfeus, J. J. Phys. Chem. 1987,
91, 5608-5616.
(18) Carilla, J.; Fajar´ı, L. l.; Julia´, L.; Riera, J.; Viadel, L. l. Tetrahedron
Lett. 1994, 35, 6529-6532. Teruel, L.; Viadel, L. l.; Carilla, J.; Fajar´ı, L.
l.; Brillas, E.; San˜e´, J.; Rius, J.; Julia´, L. J. Org. Chem. 1996, 61, 6063-
6066. Carilla, J.; Fajar´ı, L. l.; Julia´, L.; San˜e´, J.; Rius, J. Tetrahedron 1996,
52, 7013-7024. Viadel, L. l.; Carilla, J.; Brillas, E.; Labarta, A.; Julia´, L.
J. Mater. Chem. 1998, 8, 1165-1172. Domingo, V. M.; Burdons, X.; Brillas,
E.; Carilla, J.; Rius, J.; Torrelles, X.; Julia´, L. J. Org. Chem. 2000, 65,
6847-6855. Carriedo, G. A.; Garc´ıa Alonso, F. J.; Go´mez Elipe, P.; Brillas,
E.; Julia´, L. Org. Lett. 2001, 3, 1625-1628. Torres, J. L.; Varela, B.; Brillas,
E.; Julia´, L. J. Chem. Soc., Chem. Commun. 2003, 74-75. Gabino, G. A.;
Garc´ıa Alonso, F. J.; Go´mez Elipe, P.; Brillas, E.; Labarta, A.; Julia´, L. J.
Org. Chem. 2004, 69, 99-104. Jime´nez, A.; Selga, A.; Torres, J. L.; Julia´,
L. Org. Lett. 2004, 6, 4583-4586.
7524 J. Org. Chem., Vol. 72, No. 20, 2007

Adducts of Carbazole and Tris(2,4,6-trichlorotriphenyl)methyl Radical
SCHEME 1a
a Reagents: (i) 3,6-disubstituted carbazole, Cs2CO3, DMF; (ii) NaOH, Et2O/DMSO and then I2 for 2 and 3, NaOH, Et2O/DMSO and then 2,3-dicyano-
4,5-dichloroquinone for 4 or Bu4NOH, THF, and then tetrachloro-p-quinone for 5.
exchange interaction between the nitroxide doublet ground state
and the excited singlet state of the fluorophore.19 For this reason,
many nitroxide-fluorophore adducts are applied as optical
sensors of radicals and redox reactions.20 However, radical
adduct 1• shows good luminescent properties with efficiencies
approximately as high as those of the parent N-H-carbazole and
emission wavelengths dramatically shifted to the red region (for
instance, λ ) 334/350 nm for N-H-carbazole and λ ) 628 nm
for 1• in cyclohexane). The different behavior of 1• with regard
to the nitroxide radicals is that the fluorophore group in 1• is a
doublet-excited-state as the trivalent carbon atom is being part
of the chromophore. The preparation of the reported adduct 1•
has allowed assembly in one species of the redox properties
and paramagnetic character of the TTM radical and the
luminescent and hole-conductivity properties of the carbazole
in view of their potential applications as chemosensor of redox
processes and/or light-emitting diodes (LEDs). Reduction of the
adduct 1• leads to the formation of a diamagnetic product
insensitive to the electron paramagnetic resonance (EPR)
spectroscopy and resulting in a shift from the red to the blue
region in the luminescence emission (the wavelength of the
emission of the diamagnetic product is practically the same value
of the N-H-carbazole). Furthermore, stable organic radicals are
intensively investigated due to particular features induced by
the presence of an unpaired electron. As part of our research in
these multifunctional species, we have focused our efforts in
the preparation of new entities derived from radical adduct 1•
to modulate their redox and optical properties by simply
introducing electron donors and electron acceptors into the
carbazole subunit. Here, we report on the synthesis, absorption
spectra, luminescence properties, redox behavior, and EPR
spectra of novel stable free radical adducts 2•-6•, and the
preparation, absorption spectra and luminescent properties of
their diamagnetic precursors 2-6 as model compounds.
Results and Discussion
Synthesis. The experimental methods to prepare the radical
adducts 2•-7• of the TTM series are displayed in three different
schemes. Scheme 1 shows the synthesis of radical adducts 2•-
5• following the classical method carried out to prepare the
parent adduct 1•. Therefore, the TTM radical with an excess of
the 3,6-disubstituted carbazole in the presence of the appropriate
base, cesium carbonate, in boiling dimethylformamide as
solvent, followed by hydrolysis with an excess of diluted
hydrochloric acid gave a mixture of the corresponding carba-
zolyltriphenylmethane (RHcarbazolyl-TTM), with moderate
yield, and RHTTM. Next, RHcarbazolyl-TTMs 2-4 in dim-
ethylsulfoxide/diethyl ether with sodium hydroxide and then
with iodine or 2,3-dicyano-4,5-dichloroquinone and RHcarba-
zolyl-TTM 5 in tetrahydrofuran with an aqueous solution of
tetrabutylammonium hydroxide (TBAH) followed by oxidation
with 2,3,5,6-tetrachloro-p-benzoquinone rendered pure adducts
2•-5• as nicely colored crystalline solids which are stable in
solid melting at high temperatures with decomposition (see the
Experimental Section). This is an interesting coupling reaction
between the carbazole nitrogen and a p-carbon atom of the TTM
radical with the substitution of a chlorine atom. The presence
of RHTTM as a byproduct in all these experiments suggests
that some sort of radical mechanism is operative in these
reactions. Consequently, it seems that the carbazole molecule
in basic medium is oxidized to the N-carbazolyl radical by
electron transfer to TTM to form RHTTM after hydrolysis, and
then the carbazolyl radical couples with another TTM to give
the diamagnetic species RHcarbazolylTTM after further reduc-
tion with more carbazole. This mechanism has been confirmed
by two experimental tests: (1) RHTTM does not react with
carbazole in the same conditions, and (2) the coupling reaction
of carbazole with bis(2,6-dichlorophenyl)(2,4,6-trichlorophenyl)-
methyl radical (8•), which shows two free para positions, yields
besides the RHTTM as byproduct the RHcarbazolylTTM 9 as
(19) Green, J. A.; Singer, L. A.; Parks, J. H. J. Chem. Phys. 1973, 58,
2690-2695. Green, J. A.; Singer, L. A. J. Am. Chem. Soc. 1974, 96, 2730-
2733. Watkins, A. R. Chem. Phys. Lett. 1974, 29, 526-528. Kuzmin, V.
A.; Tatikolov, A. S. Chem. Phys. Lett. 1977, 51, 45-47. Chattopadhyay,
S. K.; Das, P. K.; Hug, G. L. J. Am. Chem. Soc. 1983, 105, 6205-6210.
London, E. Mol. Cell. Biochem. 1982, 45, 181-188. Atik, S. S.; Singer, L.
A. J. Am. Chem. Soc. 1978, 100, 3234-3235. Scaiano, J. C.; Paraskevopou-
los, C. I. Can. J. Chem. 1984, 62, 2351-2354.
(20) Blough, N. V.; Simpson, D. J. J. Am. Chem. Soc. 1988, 110, 1915-
1917. Herbelin, S. E.; Blough, J. Phys. Chem. B 1998, 102, 8170-8176.
Lozinsky, E. N. V.; Martin, V. V.; Berezina, T. A.; Shames, A. I.; Weis,
A. L.; Likhtenshtein, G. I. J. Biochem. Biophys. Methods 1999, 38, 29-
42. Ziessel, R.; Stroh, C. Org. Lett. 2003, 5, 2397-2400.
J. Org. Chem, Vol. 72, No. 20, 2007 7525

Velasco et al.
SCHEME 2
SCHEME 3a
a Reagents: (i) N-bromosuccinimide, silica gel, CH2Cl2; (ii) SO2Cl2, CH2Cl2; (iii) CH3COCl, AlCl3, CS2; (iv) Zn, HgCl2, HCl, toluene; (v) Bu4NOH,
THF, and then tetrachloro-p-quinone.
SCHEME 4a
a result of the substitution of one p-hydrogen by the carbazole
nitrogen and not the p-chlorine of the other phenyl substituent.
The suggested mechanism is shown in the Scheme 2. In the
first step, the electron transfer gives most probably the corre-
sponding anion 8- that is then protonated to 8. The second step
presents a simple coupling between two radicals with further
rearrangement to adduct 9•.21
Direct bromination of adduct 1• with N-bromosuccinimide
in CH2Cl2 in the presence of silica gel gives dibromocarba-
zolylTTM radical 3•. A Friedel-Crafts reaction on adduct 1•
with acetyl chloride in carbon disulfide in the presence of AlCl3
leads to adduct 6•. Both radical adducts 3• and 6• are obtained
in excellent yields. DichlorocarbazolylTTM radical 7• is obtained
with moderate yield by treatment of adduct 1• with sulfuryl
chloride in CH2Cl2. These new radicals are prepared by
substitution reactions on the carbazolyl moiety of 1• without
impairment of the radical character of the molecule. Reduction
of the carbonyl groups of 6• with an amalgam of Zn-Hg gives
the triphenylmethane 5. In this reaction, besides the reduction
of the carbonyl group by a Clemmensen reaction, the trivalent
carbon atom is also reduced to form the diamagnetic compound
a Reagents: (i) SO2Cl2, CH2Cl2; (ii) Bu4NOH, THF, and then tetrachloro-
p-quinone.
5. Treatment of 5 with an aqueous solution of TBAH and then
with tetrachloro-1,4-benzoquinone yields adduct 5• (Scheme 3).
Chlorination of RHTTM with sulfuryl chloride in CH2Cl2 gives
an excellent yield of the triphenylmethane 7 which yields adduct
7• by neutralization with TBAH and then oxidation with
tetrachloro-1,4-benzoquinone (Scheme 4).
All these radical adducts 2•-7• are colored crystalline solids
with high thermal stability (they show high melting points by
DSC analysis without decomposition; they start to decompose
when they melt; see Experimental section and Figures S19-
S24, Supporting Information), and have been fully characterized.
(21) Castellanos, S.; Lo´pez, M.; Julia´, L. Unpublished results.
7526 J. Org. Chem., Vol. 72, No. 20, 2007

Adducts of Carbazole and Tris(2,4,6-trichlorotriphenyl)methyl Radical
FIGURE 1. EPR spectrum of radical adduct 6•: (black) 6• in CH2Cl2
solution at 174 K; (red) computer simulation.
TABLE 1. g Values and Hyperfine Coupling Constants in Gauss
for Radical Adducts 1•-7• in CH2Cl2 (∼10-3 M)a
adduct
gb
1H
13C(R)c
13C(arom)c
Hpp
1•d
2•
3•
4•
5•
6•
7•
2.0032
2.0031
2.0032
2.0034
2.0033
2.0032
2.0034
1.20
1.20
1.23
1.28
1.20
1.20
1.25
28.9
28.3
26.0
27.5
27.9
27.9
28.8
10.70
10.70
10.65
10.55
10.50
10.50
10.50
0.60
0.60
0.66
0.68
0.65
0.65
0.65
FIGURE 2. Total atomic spin densities of radical 1•.
carbazolyl ring. These results suggest that the distribution of
the semioccupied molecular orbital (SOMO) in these molecules
is localized mainly around the central carbon atom and is not
influenced by the carbazolyl ring. In fact, X-ray analysis of the
molecular structure of TTM radical indicated that the phenyl
rings are twisted around their bonds with the central carbon
atom (angles about 48°) due to the presence of six chlorine
atoms in the ortho position, adopting a propeller-like conforma-
tion.17
a The hfc constants for six 1H in meta and 13C(arom) (adjacent to
R-carbon) and values for ∆Hpp (peak to peak line width) are determined at
160 ( 5 K and checked by computer simulation. b g values are measured
against dpph (2.0037 ( 0.0002) at 298 K. c Natural abundance of 13C
isotope: 1.10%. d Taken from ref 14.
Electron Paramagnetic Resonance. X-band EPR spectra of
the carbazolyl-TTM radical adducts 2•-7• are recorded in CH2-
Cl2 solution (∼10-3-10-4 M) at 298 ( 3 K and 160 ( 15 K,
and their spectral data are reported in Table 1 together with the
data for adduct 1•. In all cases, g values are similar and very
close to that of the TTM radical (g ) 2.0034 ( 0.0002) and of
the free electron (ge ) 2.0023), in agreement with the expected
small spin-orbit interaction. All of the spectra at room
temperature consisted of a broad and single line, along with a
small equidistant pair of lines in both sides of the main spectrum.
This small pair corresponds to the strong coupling of the free
electron with the R-13C nucleus, and its values are listed in Table
1. At low temperature, the spectra showed an overlapped
multiplet of very close 7 lines corresponding to the weak
coupling with the six equivalent aromatic hydrogens in the meta
positions, and two weak multiplets in both sides of the central
multiplet attributed to the coupling with the three bridgehead-
13C nuclei adjacents to the R-carbon atom. Values for all of
these couplings are also reported in Table 1. As an example,
Figure 1 shows the spectrum of the adduct 6• in CH2Cl2 solution
at 174 K (EPR spectra of radical adducts 2•-5• and 7• are
collected in Figures S13-S18, Supporting Information).
Two important points come from an analysis of data given
in Table 1. First, relatively large values of the coupling of the
free electron with R and bridgehead 13C atoms, small values
with the m-hydrogens, and no appreciable values with the
carbazolyl ring can be observed. Second, all of the radicals show
spectral parameters very similar irrespective of the different
electron-donor and electron-withdrawing substituents in the
carbazolyl ring. Moreover, all of the parameters displayed in
Table 1 are also very similar to those of TTM radical,
independent of the substitution of a p-chlorine atom by the
To discuss the coupling constants of the free electron with
the m-hydrogens and with the 13C nuclei in detail, the DFT
calculations of the geometry and spin density distribution for
adduct 1• were performed by the UB3LYP/6-31G method.
Dihedral angles between phenyl groups and the plane defined
by the central sp2-carbon atom, 45.7° 48.5°, and 48.9°, are in
good agreement with those observed for the molecular structure
of the TTM radical (48.1°, 47.1°, and 48.1°) by X-ray
crystallographic analysis. In addition, the carbazolyl ring is also
twisted an angle of -48.1° around its N-C bond with the
phenyl ring. The total atomic spin densities are illustrated in
Figure2. The spin density resides mainly on the trivalent carbon
atom since the out-of-plane torsions of the phenyl rings make
the free electron be poorly delocalized on them and the spin
density has practically no appreciable value on the carbazolyl
ring.
Electrochemical Studies. Cyclic voltammetry (CV) is used
to investigate the redox potentials of these new carbazolyl-TTM
radical adducts 2•-7• to know their electrochemical properties
and their electronic structure. Cyclic voltammograms were
recorded in CH2Cl2 solution (∼10-3 M) containing tetrabuty-
lammonium perchlorate (0.1 M) as supporting electrolyte on a
platinum disk as working electrode using a saturated calomel
electrode (SCE) as reference electrode. The voltammograms of
each radical displayed two quasireversible redox pairs, one
corresponding to its reduction (O1/R1) and the other one to its
oxidation (O2/R2), which are attributed to the equilibrium
reactions involving the addition/removal of one electron to/from
the trivalent central carbon atom to form its stable anion and
cation, respectively (Scheme 5).
Values of the electrochemical parameters are compiled in
Table 2 together with those for adduct 1•,14 and Figure 3 shows
J. Org. Chem, Vol. 72, No. 20, 2007 7527

Velasco et al.
TABLE 3. UV-vis Absorption Data of the Spectra of Radical
Adducts 1•-7• in CHCl3 and Anion Adducts 1--7- in THF
SCHEME 5
λ
maxnm (ꢀ)a
(anion)
adduct
λ
maxnm (ꢀ)a
1•b
2•
3•
4•
5•
6•
7•
374 (32 700), 560 (sh) (2700), 598 (3700)
373 (32 600), 647 (4400)
374 (30 700), 558 (sh) (2410), 585 (2840)
373 (30 700), 552 (1460)
375 (27 000), 581 (sh) (2160), 622 (3820)
373 (27 900), 543 (1840), 559 (1840)
374 (32 300), 556 (sh) (2190), 586 (2440)
508 (36 300)
506 (33 100)
506 (38 400)
507 (32 200)
506 (36 600)
509 (31 000)
510 (33 300)
TABLE 2. Standard Potential for the Redox Pair Related to the
Reduction (O1/R1) and Oxidation (O2/R2) of Radical Adducts 1•-7•,a
p
Difference between Their Anodic (Eap) and Cathodic (Ec ) Peak
a Units: dm3 mol-1 cm-1 b Values taken from ref 14.
.
Potentials, Electron Affinities, and Ionization Potentials
Eo(O1/R1)b (V)
Eo(O2/R2)b (V)
c
c
adduct ((Epa - Ep )c (mV)) ((Epa - Ep )c (mV)) EA (eV) IP (eV)
from their standard potentials of the O1/R1 and O2/R2 pairs,
respectively, taking a value of -4.8 eV as the SCE energy level
relative to the vacuum level.22
1•d
2•
3•
4•
5•
6•
7•
-0.52 (130)
-0.54 (100)
-0.48 (110)
-0.42 (140)
-0.54 (120)
-0.47 (130)
-0.48 (140)
1.03 (130)
0.86 (120)
1.12 (100)
1.27 (120)
0.95 (110)
1.18 (140)
1.11 (120)
4.28
4.26
4.32
4.38
4.26
4.33
4.32
5.83
5.66
5.92
6.07
5.75
5.98
5.91
Optical Properties. The spectral data of the UV-vis
absorption spectra of carbazolyl-TTM radical adducts 1•-7• in
CHCl3 solutions are shown in Table 3. Two absorption bands
are associated with the radical character of these radicals. The
high-energy band corresponds to a π f π* transition by virtue
of their large molar extinction coefficients. This band at λ ∼
375 nm is not sensitive to the carbazolyl substituent. The second
and very weak band with a slight multiplet structure is sensitive
to the carbazolyl substituent. The absorption shifts from blue
to red following the order 4• < 6• < 7• ∼ 3• < 1• < 5• < 2•
depending on the electronic nature of the substituent. The
alkoxy-substituted adduct 2• is red-shifted 49 nm compared to
1•, which reveals a great interaction of the electron-donating
methoxy moiety in the ground state, whereas the cyano-
substituted radical 4• is blue-shifted 46 nm with regard to 1•
due to the strong electron-withdrawing nature of the cyano
group. The significantly large value of this absorption band in
2• and the absence of vibronic structure suggest the formation
of an intramolecular charge transfer from the electron-rich
carbazolyl ring to the trivalent carbon atom.
a CH2Cl2 solution (∼10-3 M) with Bu4NClO4 (0.1 M) as background
electrolyte on Pt electrode. b Potential values versus SCE (saturated calomel
electrode). c Values at a scan rate of 100 mV s-1
.
d Values taken from ref
14.
The chemical reduction and oxidation of adducts 1•-7• were
carried out by reaction in aqueous tetrahydrofuran solution to
anion adducts 1--7- by one-electron reduction with tetrabu-
tylammonium hydroxide23 and by the reaction in CH2Cl2 to
cation adducts 1+-7+ with antimony (V) pentachloride. Both
series of charged adducts are stable in solution, and their UV-
vis spectra have been registered. The absorption data of the
spectra of anion adducts are shown in Table 3. All of them
present a single and broad band with a maximum around 508
nm. The cation adducts show more complex spectra, and they
deserve more research that is now in progress in our laboratories.
The luminescence emission spectra of radical adducts 1• and
3•-7• are displayed in Figure 4. Tables 4 and 5 summarize the
optical properties of radical adducts 1•-7• and their diamagnetic
precursors 1-7, respectively, determined from UV-vis and
fluorescence measurements in a nonpolar solvent such as
cyclohexane and in the one more polar CHCl3. Note that the
absorption maxima wavelength of the lowest energy transition
for adducts 1•-7• are only reported in Table 4 because this is
the only one sensitive to the polarity of the solvent. These
transitions undergo small (1-5 nm) shifts in adducts 1•, 3•, and
FIGURE 3. Cyclic voltammograms recorded for a 1 mM radical
adduct 6• solution in CH2Cl2 with TBAP 0.1 M on Pt at 25 C. (a)
Oxidation at an initial and final potential of 0.600 V and a reversal
potential of 1.400 V. (b) Reduction at an initial and final potential of
-0.200 V and a reversal potential of -0.800 V. Scan rate: (a) 200,
(b) 100, (c) 50, (d) 20 mV s-1
.
the cyclic voltammograms obtained for adduct 6• (voltammo-
grams for adducts 2•-7•, see Figures S1-S12, Supporting
Information). Each redox process, either in the cathodic or
anodic region, is quasireversible because the difference between
their anodic and cathodic peak potentials is always higher than
the theoretical value of 59.2 mV expected for a one-electron
reversible process and increases gradually as rising scan rate.
Its standard potential (E°) was determined as the average of
a
c
the anodic (Ep ) and cathodic (Ep ) peak potentials. The E° value
for the O2/R2 pair of the anodic region becomes more positive
in the sequence 2• < 5• < 1• < 7• ∼ 3• < 6• < 4•, in accordance
with the electron-donating ability of substituents at the carba-
zolyl ring, adduct 2• being the more easily oxidized. For the
same reason, the E° value for the O1/R1 pair of the cathodic
region is shifted to more negative potential following the order
4• < 6• < 7• ∼ 3• < 1• < 5• ∼ 2•, adduct 4• being the more
easily reduced. Table 2 also collects the electron affinity (EA)
and ionization potential (IP) values for adducts 1•-7• estimated
(22) Alam, M. M.; Jenekhe, S. A. J. Phys. Chem. B 2002, 106, 11172-
11177.
(23) The reducing properties of hydroxide anion on radicals of the
perchlorotriphenylmethyl (PTM) series in nonaqueous solvents are well-
known: Ballester, M. AdV. Phys. Org. Chem. 1989, 25, 267-445. Ballester,
M.; Pascual, I. J. Org. Chem. 1991, 56, 841-844.
7528 J. Org. Chem., Vol. 72, No. 20, 2007

Adducts of Carbazole and Tris(2,4,6-trichlorotriphenyl)methyl Radical
FIGURE 4. Normalized fluorescence emission spectra of radical adducts recorded in (left) cyclohexane solution; 1• black, 5• red, 3• blue, 7• green;
(right): chloroform solution; 1• black, 6• red, 3• blue, 7• green; at room temperature.
TABLE 4. UV/vis and Luminescence Spectral Data for Radical
charge transfer from the carbazolyl ring to the trivalent carbon
atom in both radicals. It is known that the fluorescence efficiency
in the intramolecular charge transfer states decrease with
increasing strength of the transfer, and this is more significant
in polar solvents.24 A similar observation is also confirmed with
the dramatic decrease of the fluorescence efficiency and the
significant red-shifted emission in the luminescence of adduct
1• and in less extension to the luminescence of the adducts 3•
and 7• with solvent polarity. The values of the Stokes shift (gap
between the maxima of the first absorption and emission bands)
of the emission of adducts 1•, 3•, and 7• were found to
dramatically increase with the polarity of the solvent, thus
supporting the charge-transfer character of their excited states.
All of these observations suggest that adducts 1•, 2•, 3•, 5•, and
7• undergo structural reorientation in the excited state to adopt
most probably a more planar conformation to facilitate a charge
transfer from the carbazolyl moiety to the trivalent carbon atom.
In accordance with it, the structure of the excited state should
be in resonance with the canonical structures A and B:
Adducts 1•-7•
a
λabs
λexc
λem
Stokes shift
(cm-1
)
b
adduct
solvent
(nm) (nm) (nm)
ΦF
1•c
cyclohexane
chloroform
cyclohexane
chloroform
cyclohexane
chloroform
toluene
chloroform
cyclohexane
chloroform
toluene
603
598
667
647
588
585
557
552
633
622
578
559
587
586
515
515
300
300
464
427
471
471
450
450
450
450
427
427
628
680
0.53
0.02
0
660
2166
2•
3•
4•
5•
6•
7•
0
615
654
601
591
661
0.45
0.21
0.165
0.12
0.29
0
0.48
0.38
0.34
0.22
746
1803
1314
1195
669
625
618
615
653
1301
1708
776
chloroform
cyclohexane
chloroform
1751
a The less energetic band in the absorption spectra. b Quantum yield of
luminescence. c Values taken from ref 14.
TABLE 5. UV/vis and Luminescence Spectral Data for the
Diamagnetic Precursors 1-7
b
precursor
solvent
λabsa (nm)
λ
exc (nm)
λ
em (nm)
ΦF
1c
3
cyclohexane
cyclohexane
chloroform
cyclohexane
chloroform
cyclohexane
chloroform
cyclohexane
chloroform
cyclohexane
chloroform
335
352
353
insol
340
344
346
insol
296
352
353
300
296
301
338/353
358/375
368/379
0.05
0.003
0.006
4
5
6
7
304
296
296
346/361
350/363
359
0.20
0.086
0.009
301
299
301
0
The luminescence emission of adducts 4• and 6• should be
different because of the electron-withdrawing character of the
substituents in the carbazolyl ring. Since these radicals are not
soluble in cyclohexane, toluene was chosen as a good solvent
of low polarity. Both adducts 4• and 6• show fluorescence
efficiency in toluene and chloroform, being a little lower in
chloroform, and a blue-shifted emission with the polarity of the
solvent, an opposite behavior to that shown by the other radicals.
357/374
361/378
0.041
0.032
a The less energetic band in the absorption spectra. b Quantum yield of
luminescence. c Values taken from ref 14.
7• from cyclohexane to chloroform, whereas there is a blue shift
in 5• (11 nm) and more significant shift in 2• (20 nm). Nothing
is said with regard to adducts 4• and 6• due to their insolubility
in cyclohexane. If values of both Tables 4 and 5 are compared,
fluorescence emission is much more intense and dramatically
red-shifted in radicals than in their precursors. In those radicals
soluble in both solvents, the luminescence quantum yield is
higher in cyclohexane than in chloroform. The luminescence
of adducts 2• and 5• with electron-donor substituents in the
carbazolyl ring deserves special mention. The complete absence
of emission of 2• in both solvents and of 5• in chloroform
suggests, at least in part, the existence of a donor-acceptor
nature of the excited state with the consequent intramolecular
Conclusions
We have established a new synthetic method to obtain a series
of new carbazolyl derivatives with a pendant stable radical of
the TTM series, radical adducts 2•-7•. This method deals with
the coupling between the carbazole nitrogen and a p-carbon
center of the parent TTM radical. The results presented suggest
(24) Jenekhe, S. A.; Lu, L.; Alam, M. M. Macromolecules 2001, 34,
7315-7324.
J. Org. Chem, Vol. 72, No. 20, 2007 7529

Velasco et al.
gel with hexane to give 3,6-diethylcarbazole (417 mg, 47%): IR
(KBr) 3417 (m), 2968 (m), 2926 (w), 2868 (w), 2853 (w), 1866
(w), 1765 (w), 1610 (w), 1574 (w), 1494 (s), 1465 (s), 1371 (w),
1326 (m), 1303 (m), 1248 (s), 1147 (w), 1055 (w), 920 (w), 883
that a radical mechanism is operative in this kind of reaction.
Some of the adducts, 2•-5•, are prepared by coupling between
the TTM radical and the disubstituted NH-carbazoles, although
some of them and other new ones 3•, 6•, and 7• are prepared by
introducing the substituents into the carbazole ring once the
radical adduct is made, without impairment of the radical
character of the molecule. The EPR spectra, electrochemical
properties, absorption spectra, and luminescence properties of
these adducts have been studied. The redox behavior of these
adducts exhibits electrochemical amphotericity being reduced
and oxidized to their corresponding stable charged species in
quasireversible processes. UV-vis spectra show the bands
associated with the radical character of these adducts typical of
the absorptions found in the stable radicals of the TTM series,
involving two one-electron transitions from SOMO to LUMO
and HOMO to LUMO, which correspond to the two first excited
configurations. One of these transitions is sensitive to the
carbazolyl substituents. All of the radical adducts except 2• show
very significant luminescence properties, covering the red
spectral band of the emission. They show a dramatic large red
shift in emission when compared to their diamagnetic hydro-
carbon counterparts, and the results evidence that the nature of
the substituent controls the fine-tuning of the emission color.
Furthermore, the radiative emission in those adducts with
electron-releasing substituents in the carbazole ring is red-shifted
with the polarity of the solvent and blue-shifted in those adducts
with electron-withdrawing substituents in the carbazole. These
facts indicate the donor-acceptor nature of the excited states
in the electron-rich carbazole adducts. The EPR parameters of
these radical adducts show practically an inestimable variation
with the substituents in the carbazole. This fact suggests that
delocalization into the carbazole is very limited; in fact, the
hyperfine coupling to the N atom is imperceptible. From the
results depicted in this paper, we have established structural
groundwork to aid in the further design of new materials
applicable in areas, where carbazole itself has demonstrated its
usefulness.
1
(s), 813 (s), 752 (w) cm-1; H NMR (300 MHz; CDCl3) 7.89 (s,
2H), 7.85 (s, 1H, NH), 7.32 (d, J ) 8.1 Hz, 2H), 7.25 (d, J ) 8.1
Hz, 2H), 2.83 (q, J ) 7.8 Hz, 4H), 1.35 (t, J ) 7.8 Hz, 6H, CH3)
ppm; EI-HRMS calcd for C16H17N 223.136100, found m/z
223.136365.
[2,6-Dichloro-4-(3,6-dimethoxy-N-carbazolyl)phenyl]bis(2,4,6-
trichlorophenyl)methyl Radical Adduct (2•). (a) [2,6-Dichloro-
4-(3,6-dimethoxy-N-carbazolyl)phenyl]bis(2,4,6-trichlorophenyl)-
methane (2). A mixture of 3,6-dimethoxy-9H-carbazole25 (200 mg;
0.9 mmol), tris(2,4,6-trichlorophenyl)methyl radical (486 mg; 0.9
mmol), anhydrous Cs2CO3 (486 mg; 1.4 mmol), and DMF (5 mL)
was stirred at reflux (2.5 h) in an inert atmosphere and in the dark.
The resulting mixture was poured into an excess of diluted aqueous
HCl acid, and the precipitate was filtered off. The solid was
chromatographed in silica gel with hexane/chloroform (1:2) to give
tris(2,4,6-trichlorophenyl)methane (212 mg; 44%), identified by IR,
and 2 (186 mg; 28%): IR (KBr) 3074 (w), 2934 (w), 2829 (w),
1594 (m), 1577 (m), 1542 (m), 1490 (s), 1471 (s), 1433 (m), 1372
(m), 1327 (m), 1205 (s), 1175 (m), 1157 (m), 1035 (m), 858 (m),
1
836 (m), 805 (s), 754 (m) cm-1; H NMR (300 MHz; CDCl3) δ
3.95 (s, 6H), 6.83 (s, 1H), 7.07 (dd, 2H, J ) 8.8 Hz, J′ ) 2.5 Hz),
7.27 (d, 1H, J ) 2.1 Hz), 7.29 (d, 1H, J ) 2.1 Hz), 7.37 (d, 2H,
J ) 8.8 Hz), 7.40 (d, 1H, J ) 2.4 Hz), 7.42 (d, 1H, J ) 2.4 Hz),
7.45 (d, 1H, J ) 2.4 Hz), 7.52 (d, 2H, J ) 2.4 Hz), 7.58 (d, 1H,
J ) 2.1 Hz); MS (EI) 745.1 (M+).
(b) Radical Adduct 2•. A mixture of 2 (85 mg; 0,11 mmols)
and powdered sodium hydroxide (230 mg) in ethyl ether-
dimethylsulfoxide (15 mL; 2:1) was shaken (48 h) at rt. The mixture
was filtered into a solution of iodine (300 mg) in ethyl ether (20
mL), and the solution was stirred in the dark (1 h), washed with an
excess of aqueous solution of sodium bisulfite and H2O, dried,
and evaporated to dryness, giving a residue which was chromato-
graphed in silica gel with hexane/chloroform (1:2) to give adduct
2• (71 mg; 85%): mp 260 °C dec (DSC); IR (KBr) 3068 (w), 2931
(w), 2827 (w), 1577 (s), 1554 (m), 1523 (m), 1490 (s), 1471 (s)
1431 (m), 1371 (m), 1327 (m), 1204 (s), 1157 (m), 1036 (m), 857
(m), 829 (m), 809 (s) cm-1; UV (CHCl3) λmax/nm (ꢀ/L mol-1
cm-1) 309 (24 600), 375 (32 400), 450 (sh) (2800), 647 (440); CI-
HRMS calcd for C33H18Cl8NO2 m/z 739.884576, found
739.885621.
[2,6-Dichloro-4-(3,6-dibromo-N-carbazolyl)phenyl]bis(2,4,6-
trichlorophenyl)methyl radical adduct (3•). (1) From Tris(2,4,6-
trichlorophenyl)methyl Radical (TTM). (a) [2,6-Dichloro-4-(3,6-
dibromo-N-carbazolyl)phenyl]bis(2,4,6-trichlorophenyl)meth-
ane (3). A mixture of 3,6-dibromo-9H-carbazole26 (400 mg; 1.2
mmol), TTM (500 mg; 0.9 mmol), anhydrous Cs2CO3 (500 mg;
1.5 mmol), and DMF (5 mL) was stirred at reflux (2 h) in an inert
atmosphere and in the dark. The resulting mixture was poured into
an excess of diluted aqueous HCl acid, and the precipitate was
filtered off. The solid was chromatographed in silica gel with hexane
and 30% CHCl3 to give tris(2,4,6-trichlorophenyl)methane (100 mg;
20%) identified by IR and 3 (245 mg; 33%): mp 346 °C (DSC);
IR (KBr) 3075 (w), 1594 (s), 1577 (s), 1542 (s), 1468 (s), 1433
(m), 1371 (m), 1279 (s), 1229 (m), 1142 (m), 1056 (m), 1020 (m),
897 (m), 860 (s), 826 (s), 802 (s), 634 (m), 608 (m) cm-1; 1H NMR
(300 MHz; CDCl3) δ 6.85 (s, 1H), 7.27-7.30 (m, 4H), 7.40-7.41
(m, 2H), 7.43 (d, 1H, J ) 2.4 Hz), 7.54 (d, 2H, J ) 1.8 Hz), 7.56
(d, 1H, J ) 2.1 Hz), 8.18 (d, 2H, J ) 1.8 Hz); UV (chloroform)
λmax /nm (/L mol-1 cm-1) 303 (27 800), 338 (4500), 353 (4630)
nm; MS (IE) 843.6 (M+).
Experimental Section
3,6-Diacetylcarbazole. Acetyl chloride (2.8 mL; 39.6 mmol) was
added to a stirred mixture of carbazole (3 g; 18 mmol), AlCl3 (5.33
mg; 40 mmol), and CS2 (45 mL) at reflux in an anhydrous
atmosphere. The mixture was further refluxed (6 h), and then the
solvent was evaporated off and the crude was chromatographed in
silica gel with chloroform to give 3,6-diacetylcarbazole (3.38 g,
75%): IR (KBr) 3277 (s), 1673 (s), 1662 (s), 1623 (s), 1599 (s),
1490 (w), 1451 (w), 1406 (w), 1358 (m), 1293 (m), 1267 (m), 1240
(m), 1227 (m), 1140 (w), 1127 (w), 1053 (w), 1021 (w), 956 (w),
1
904 (w), 882 (w), 829 (w), 820 (w), 802 (w), 638 (w) cm-1; H
NMR (300 MHz; CDCl3) δ 8.79 (d, J ) 1.5 Hz, 2H), 8.15 (dd, J
) 8.4 Hz, J ) 1.5 Hz, 2H), 7.51 (d, J ) 8.4 Hz, 2H), 2.77 (s, 6H,
CH3); UV (cyclohexane) λmax/nm (ꢀ/L mol-1 cm-1) 260 (34 800),
292 (20 600), 325 (10 300) nm; EI-HRMS calcd for C16H13NO2
252.097984, found m/z 252.097546.
3,6-Diethylcarbazole. A mixture of HgCl2 (2.5 mg), metallic
Zn (26 g), and concentrated aqueous HCl acid (2.5 mL of HCl in
50 mL of water) was stirred at rt (15 min) to generate an amalgam.
Concentrated aqueous HCl acid (40 mL) and 3,6-diacetylcarbazole
(1 g; 5.99 mmol) were added, and the mixture was stirred vigorously
(2 h) and then allowed to stand (12 h). Toluene (15 mL) was added,
and the mixture was stirred to reflux (48 h). The resultant phases
were separated, the aqueous phase was extracted with diethyl ether,
and the combined organic phases were washed with water, dried,
and evaporated to dryness. The residue was filtrated through silica
(25) Hsieh, B. R.; Litt, M. H. Macromolecules 1986, 19, 516-520.
(26) Smith, K.; James, D. M.; Mistry, A. G.; Bye, M. R.; Faulkner, J.
Tetrahedron 1992, 48, 7479-7488.
7530 J. Org. Chem., Vol. 72, No. 20, 2007

Adducts of Carbazole and Tris(2,4,6-trichlorotriphenyl)methyl Radical
(b) Radical Adduct 3•. A mixture of 3 (100 mg; 0,12 mmols),
powdered sodium hydroxide (300 mg), and diethyl ether-dimethyl
sulfoxide (15 mL; 2:1) was shaken (48 h) at rt. The mixture was
filtered into a solution of iodine (400 mg) in diethyl ether (20 mL),
and the solution was stirred in the dark (1 h) and then washed with
an excess of aqueous solution of sodium hydrogen sulfite and H2O,
dried, and evaporated to dryness, giving a residue which was
chromatographed in silica gel with hexane/chloroform (1:1) to give
adduct 3• (80 mg; 80%): mp 350 °C dec (DSC); IR (KBr) 3069
(w), 1577 (s), 1556 (m), 1524 (s), 1468 (s), 1441 (m), 1429 (m),
1370 (m), 1279 (s), 1227 (s), 1182 (m), 1137 (m), 1021 (m), 861
(DSC); IR (KBr) 3072 (w), 2961 (m), 2927 (m), 2856 (w), 1726
(w), 1594 (s), 1577 (s), 1481 (s), 1436 (w), 1372 (m), 1329 (w),
1302 (w), 1233 (m), 1191 (w), 1174 (w), 1140 (w), 1075 (w), 1057
1
(w), 922 (w), 900 (m), 857 (s), 835 (m), 806 (s) cm-1; H NMR
(300 MHz; CDCl3) δ 7.92 (s, 2H); 7.60 (d, J ) 2.1 Hz, 1H); 7.46
(d, J ) 2.1 Hz, 1H); 7.42 (d, J ) 2.1 Hz, 1H); 7.40 (d, J ) 2.1 Hz,
1H); 7.37 (d, J ) 8.4 Hz, 2H, 1-H); 7.30-7.25 (m, 4H); 6.84 (s,
1H, CH); 2.84 (q, J ) 7.5 Hz, 4H); 1.34 (t, J ) 7.5 Hz, 6H, CH3);
UV (cyclohexane) λmax/nm (ꢀ/L mol-1 cm-1) 235 (53 600), 297
(20 700), 328 (17 300), 344 (7900) nm; CI-HRMS calcd for C35H23-
Cl8N m/z 740.927966, found 740.973128.
(s), 814 (s), 802 (s) cm-1; UV (CHCl3) λmax/nm (ꢀ/L mol-1 cm-1
)
(b) Radical Adduct 5•. A mixture of 5 (115 mg; 17%), a hexane
solution of TBAH (1.5M) (0.2 mL; 0.32 mmol), and THF (7 mL)
was stirred (5 h) in an inert atmosphere at rt, and then 2,3-dichloro-
4,5-dicyane-p-benzoquinone (36 mg; 0.16 mmol) was added. The
solution was stirred in the dark (2 h) and evaporated to dryness,
giving a residue which was filtered through silica gel with hexane
to give adduct 5• (60 mg; 52%): mp 300 °C dec (DSC); IR (KBr)
2961 (m), 2927 (w), 1575 (s), 1555 (s), 1523 (s), 1479 (s), 1467
(s), 1372 (m), 1350 (m), 1329 (m), 1303 (w), 1232 (m), 1184 (m),
1136 (m), 1082 (w), 1059 (w), 925 (w), 857 (m), 811 (s), 797 (s),
761 (w) cm-1; UV (CHCl3) λmax/nm (ꢀ/L mol-1 cm-1) 240 (62 500),
297 (20 100), 375 (27 000), 452 (sh) (2250), 622 (3800); CI-HRMS
calcd for C35H22Cl8N m/z 739.919740, found 739.907785.
[2,6-Dichloro-4-(3,6-diacetyl-N-carbazolyl)phenyl]bis(2,4,6-
trichlorophenyl)methyl Radical Adduct (6•). Acetyl chloride (0.8
mL; 1.12 mmol) was added to a stirred mixture of 4-N-carbazolyl-
2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)methyl radical (200
mg; 0.29 mmol), AlCl3 (100 mg; 0.75 mmol), and CS2 (8 mL) at
reflux in an anhydrous atmosphere. The mixture was further
refluxed (2 h) and then poured into an excess of diluted aqueous
HCl acid and treated with CHCl3. The organic solution, dried and
evaporated to dryness, gave a residue which was chromatographed
in silica gel with chloroform to give radical 6• (206 mg; 89%):
mp 359 dec (DSC); IR (KBr) 3061 (w), 1678 (s), 1624 (m), 1593
(s), 1575 (s), 1554 (s), 1523 (m), 1478 (m), 1359 (m), 1290 (m),
1257 (s), 1217 (m), 1182 (m), 1137 (m), 858 (m), 815 (s), 799
(m), 757 (m); UV (CHCl3) λmax/nm (ꢀ/L mol-1 cm-1) 263 (51 700),
293 (18 800), 328 (20 400), 373 (28 700), 555 (1900); MS (EI)
768.2 (M+); CI-HRMS calcd for C35H18Cl8NO2 767.878666, found
m/z 767.888208.
[2,6-Dichloro-4-(3,6-dichloro-N-carbazolyl)phenyl]bis(2,4,6-
trichlorophenyl)methyl Radical Adduct (7•). (1) From [4-(N-
Carbazolyl)-2,6-dichlorophenyl]bis(2,4,6-trichlorophenyl)-
methane (1). (a) [2,6-Dichloro-4-(3,6-dichloro-N-carbazolyl)phenyl]
bis(2,4,6-trichlorophenyl)methane (7). A mixture of 1 (160 mg,
0.23mmol) and CH2Cl2 (3 mL) in a three-necked flask equipped
with a septum and thermometer was cooled (0 °C) with vigorous
stirring while SO2Cl2 (0.5 mL; 6 mmol) was added dropwise at
such rate that the temperature did not exceed 2 °C. Then the cooling
bath was removed, and the reaction mixture was stirred (2.5 h) at
rt. The mixture was washed with water, dried, and evaporated to
dryness to give a residue which was purified by chromatography
on silica gel eluting with hexane/chloroform (3:1) to give 7 (140
mg; 81%): mp 329 °C (DSC); IR (KBr) 3075 (w), 1594 (s), 1576
(s), 1543 (s), 1476 (s), 1435 (s), 1372 (s), 1315 (m), 1278 (s), 1229
374 (30 900), 445 (sh) (3550), 558 (sh) (2400), 586 (2800); CI-
HRMS calcd for C31H12Br2Cl8N m/z 841.680518, found 841.679882.
(2) From (4-N-Carbazolyl-2,6-dichlorophenyl)bis(2,4,6-trichlo-
rophenyl)methyl Radical Adduct (1•). To a mixture of adduct 1•
(200 mg; 0,29 mmol), silica gel (1.17 g), and anhydrous CH2Cl2
(8 mL) was added dropwise a solution of N-bromosuccinimide (100
mg; 0.58 mmol) in CH2Cl2 (10 mL) and the mixture stirred
vigorously (5 h) at rt in the dark. The mixture was filtered, and the
solution was washed with water, dried, and evaporated to dryness.
The residue was chromatographed in silica gel with hexane and
30% CHCl3 to give adduct 3• (198 mg; 80%).
[2,6-Dichloro-4-(3,6-dicyano-N-carbazolyl)phenyl]bis(2,4,6-
trichlorophenyl)methyl Radical Adduct (4•). (a) [2,6-Dichloro-
4-(3,6-dicyano-N-carbazolyl)phenyl]bis(2,4,6-trichlorophenyl)-
methane (4). A mixture of 3,6-cyano-9H-carbazole27 (300 mg; 1.38
mmol), TTM (600 mg; 1.08 mmol), anhydrous Cs2CO3 (600 mg;
1.84 mmol), and DMF (5 mL) was stirred at reflux (2 h) in an
inert atmosphere and in the dark. The resulting mixture was poured
into an excess of diluted aqueous HCl acid, and the precipitate was
filtered off. The solid was chromatographed in silica gel with CH2-
Cl2 to give tris(2,4,6-trichlorophenyl)methane (250 mg; 41%)
identified by IR and 4 (153 mg; 19%): IR (KBr) 3075(w), 2220
(s), 1730 (w), 1630 (w), 1597 (s), 1576 (m), 1542 (s), 1482 (s),
1458 (m), 1435 (w), 1372 (m), 1335 (w), 1291 (m), 1242 (s), 1189
(w), 1175 (w), 1142 (w), 1077 (w), 1027 (w), 998 (w), 902 (m),
863 (m), 856 (m), 817 (s), 808 (s), 678 (w) cm-1; CI-HRMS calcd
for C33H1335Cl637Cl2N3 m/z 734.855869, found 734.856913.
(b) Radical Adduct 4•. A mixture of 4 (100 mg; 0,14 mmols)
and powdered sodium hydroxide (250 mg) in ethyl ether-dimethyl
sulfoxide (15 mL; 2:1) was shaken (48 h) at rt. The mixture was
filtered into a solution of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone
(55 mg; 0.20 mmol) in ethyl ether (20 mL), and the solution was
stirred in the dark (2 h). The mixture was diluted with chloroform
and washed with H2O, dried, and evaporated to dryness, giving a
residue which was chromatographed in silica gel with chloroform
to give adduct 4• (70 mg; 70%): mp 379 °C dec (DSC); IR (KBr)
3062 (w), 2220 (s), 1630 (m), 1597 (m), 1577 (s), 1553 (s), 1524
(s), 1481 (s), 1457 (m), 1370 (m), 1358 (m), 1333 (w), 1292 (m),
1241 (s), 1183 (m), 1137 (m), 1083 (w), 1028 (w), 997 (w), 925
(m), 894 (w), 857 (m), 817 (s) cm-1; UV (CHCl3) λmax/nm (ꢀ/L
mol-1 cm-1) 373 (28 200), 425 (sh) (5370), 499 (1700), 552 (1450);
CI-HRMS calcd for C33H1235Cl637Cl2N3 m/z 733.848044, found
734.893018 (M+ + H).
[2,6-Dichloro-4-(3,6-diethyl-N-carbazolyl)phenyl]bis(2,4,6-
trichlorophenyl)Methyl Radical Adduct (5•). (a) [2,6-Dichloro-
4-(2,6-diethyl-N-carbazolyl)phenyl]bis(2,4,6-trichlorophenyl)-
methane (5). A mixture of 3,6-diethylcarbazole (300 mg; 1.35
mmol), TTM (500 mg; 0.9 mmol), anhydrous Cs2CO3 (500 mg;
1.5 mmol), and DMF (8 mL) was stirred at reflux (2 h) in an inert
atmosphere and in the dark. The resulting mixture was poured into
an excess of diluted aqueous HCl acid, and the precipitate was
filtered off. The solid was chormatographed in silica gel with
hexane/chloroform (9:1) to give 5 (115 mg; 17%): mp 281 °C
(m), 1141 (m), 1076 (m), 1024 (m), 900 (s), 856 (s), 804 (s) cm-1
;
1H NMR (CDCl3, 300 MHz) δ 6.85 (s, 1H), 7.28 (d, J ) 2.1 Hz,
1H), 7.30 (d, J ) 2.1 Hz, 1H), 7.33 (d, J ) 8.8 Hz, 2H), 7.40-
7.44 (m, 5H); 7.54 (d, J ) 2.1 Hz, 1H); 8.03 (d, J ) 2.1 Hz, 2H);
UV (chloroform) λmax /nm (ꢀ/L mol-1 cm-1) 302 (25 500), 339
(4400), 353 (4600) nm; MS (IE) 753.5 (M+).
(b) Radical Adduct 7•. A mixture of 7 (100 mg; 0.13 mmols),
powdered sodium hydroxide (300 mg), and diethyl ether-dimethyl
sulfoxide (15 mL; 2:1) was shaken (48 h) at rt. The mixture was
filtered into a solution of iodine (250 mg) in diethyl ether (20 mL),
and the solution was stirred in the dark (2 h) and then washed with
excess of aqueous solution of sodium hydrogen sulfite and H2O,
dried, and evaporated to dryness, giving a residue which was
(27) Patrick, D. A.; Boykin, D. W.; Wilson, W. D.; Tanious, F. A.;
Spychala, J.; Bender, B. C.; Hall, J. E.; Dykstra, C. C.; Ohemeng, K. A.;
Tidwell, R. R. Eur J. Med. Chem. 1997, 32, 781-793.
J. Org. Chem, Vol. 72, No. 20, 2007 7531

Velasco et al.
purified by column chromatography on silica gel with hexane/
chloroform (1:2) to give adduct 7• (72 mg; 72%): mp 334 °C dec
(DSC); IR (KBr) 3070 (w) 1578 (s), 1555 (s), 1524 (s), 1474 (s),
1444 (m), 1371 (m), 1316 (m), 1279 (s), 1229 (m), 1183 (m), 1138
(m), 1076 (m), 1065 (m), 1024 (m), 924 (m), 857 (s), 804 (s), 754
(m) cm-1; UV (CHCl3) λ max/nm (ꢀ/L mol-1 cm-1) 374 (32 400),
447 (sh) (2950), 556 (sh) (2200), 586 (2450); CI-HRMS calcd for
C31H12Cl10N m/z 751.779602, found 751.782961.
(2) From [4-(N-Carbazolyl)-2,6-dichlorophenyl]bis(2,4,6-
trichlorophenyl)methyl Radical Adduct (1•). A mixture of adduct
1• (43 mg, 0.063 mmol) and CH2Cl2 (4 mL) in a three-necked flask
equipped with a septum and thermometer was cooled (0 °C) and
vigorous stirring, while SO2Cl2 (0.1 mL; 1.23 mmol) was added
dropwise at such rate, that the temperature did not exceed 2 °C.
Then, the cooling bath was removed and the reaction mixture was
stirred (5 h) at rt. The mixture, washed with water, dried, and
evaporated to dryness, gave a residue which was purified by
chromatography on silica gel eluting with hexane to give adduct
7• (23 mg; 43%).
[2,6-Dichloro-4-(3,6-dibromo-N-carbazolyl)phenyl]bis(2,4,6-
trichlorophenyl)methane (3). To a mixture of 1 (0.175 g; 0.25
mmol), silica gel (1 g), and anhydrous CH2Cl2 (7 mL) was added
dropwise a solution of N-bromosuccinimide (0.091 g; 0.51 mmol)
in anhydrous CH2Cl2 (8 mL) and stirred vigorously (5 h) at rt in
the dark. The mixture was filtered, and the solution was washed
with water, dried, and evaporated to dryness. The residue was
chromatographed in silica gel with hexane and CHCl3 (30%) to
give 3 (0.145 g, 70%).
[2,6-Dichloro-4-(3,6-dicyano-N-carbazolyl)phenyl]bis(2,4,6-
trichlorophenyl)methane (4). A solution of radical adduct 4• (200
mg, 0.29 mmol) and L-ascorbic acid (102 mg, 0.58 mmol) in a
mixture of THF/H2O (12 mL, 10:1) was stirred at rt (48 h) and
then poured into an excess of diluted aqueous HCl acid and
extracted with CHCl3. The organic solution, washed with H2O, dried
over Na2SO4 anhydrous, filtered and evaporated, gave a residue
which was chromatographed on silica gel with a mixture of hexane/
chloroform (2:1) to give 4 (162 mg; 81%).
[2,6-Dichloro-4-(3,6-diacetyl-N-carbazolyl)phenyl]bis(2,4,6-
trichlorophenyl)methane (6). A mixture containing 1 (400 mg;
0.59 mmol), AlCl3 (157 mg; 1.18 mmol), and CS2 (28 mL) was
stirred at reflux in a P2O5 atmosphere. Acetyl chloride (0.1 mL;
1.48 mmol) was added and evolution of gas was observed. After 2
h of reaction, the solvent was evaporated and the crude was treated
with an ice/water/HCl mixture and extracted with chloroform. The
organic layer was dried and evaporated to dryness and the resulting
residue was chromatographed in silica gel with chloroform to give
6 (360 mg; 80%): mp 352 °C (DSC); 1H NMR (300 MHz; CDCl3)
δ 8.31 (d, J ) 1.8 Hz, 2H), 8.16 (dd, J1 ) 8.7 Hz, J2 ) 1.8 Hz,
2H), 7.59 (d, J ) 1,8 Hz, 1H), 7.47-7.42 (m, 5H), 7.32 (d, J )
1.8 Hz, 1H), 7.31 (d, J ) 1.8 Hz, 1H), 6.88 (s, 1H), 2.76 (s, 6H,
CH3) ppm; IR (KBr) 3072 (w), 1678 (s), 1625 (w), 1593 (s), 1575
(m), 1541 (m), 1480 (m), 1458 (w), 1434 (w), 1421 (w), 1371 (m),
1359 (m), 1335 (w), 1303 (w), 1288 (w), 1258 (s), 1216 (w) 1192
(w) 1174 (w), 1141 (w) 1077 (w), 1024 (w), 996 (w), 959 (w),
901 (m), 855 (m), 835(w), 816 (m), 806 (m), 677 (w), 655 (w),
619 (m) cm-1; UV (chloroform) λmax /nm (ꢀ/L mol-1 cm-1) 263
(53 200), 296 (35 000) nm; MS (IE) 769.6.
[2,6-Dichloro-4-(3,6-diethyl-N-carbazolyl)phenyl]bis(2,4,6-
trichlorophenyl)methane (5). (a) From [2,6-Dichloro-4-(2,6-
diacetyl-N-carbazolyl)phenyl]bis(2,4,6-trichlorophenyl)methyl
Radical (6•). A mixture of HgCl2 (250 mg) and metallic Zn (3 g),
HCl (0.3 mL) and water (5 mL) was stirred at rt (15 min) to generate
an amalgam. Concentrated aqueous HCl acid (4 mL) and adduct
6• (100 mg; 0.13 mmol) were added, and the mixture was stirred
vigorously (2 h) and then allowed to stand (12 h). Toluene (9 mL)
was added, and the mixture was stirred to reflux (48 h). The
resultant phases were separated, the aqueous phase was extracted
with diethyl ether, and the combined organic phases were washed
with water, dried, and evaporated to dryness. The residue was
filtrated trough silica gel with hexane to give 5 (34 mg; 35%).
(b) From [2,6-Dichloro-4-(3,6-diacetyl-N-carbazolyl)phenyl]-
bis(2,4,6-trichlorophenyl)methane (6). A mixture of HgCl2 (0.250
g), metallic Zn (3 g), water (5 mL), and concentrated aqueous HCl
acid (0.3 mL) was stirred at rt (15 min) to generate an amalgam.
Concentrated aqueous HCl acid (4 mL) and then 6 (150 mg; 0.20
mmol) were added, and the mixture was stirred vigorously (2 h)
and left deposited (12 h). Toluene (9 mL) was added, and the
mixture was stirred to reflux (24 h). The resultant phases were
separated, the aqueous phase was extracted with ether, and the
combined organic phases were washed with water, dried, and
evaporated to dryness. The residue was filtrated trough silica gel
with hexane to give 5 (105 mg; 71%).
Acknowledgment. Financial support for this research was
provided by the Ministerio de Educacio´n y Ciencia (Spain)
through Grant No. CTQ2006-15611-C02-02/BQU. S.C. grate-
fully acknowledges the Generalitat de Catalunya for a predoc-
toral grant, and M.L. thanks the Institut d’Investigacions
Qu´ımiques i Ambientals de Barcelona (CSIC) and the European
Social Fund for his I3P fellowship. We also thank the EPR
service of the Institut d’Investigacions Qu´ımiques i Ambientals
de Barcelona (CSIC) for recording the EPR spectra.
Supporting Information Available: Cyclic voltammograms
(Figures S1-S12) and EPR spectra (Figures S13-S18) for new
radical adducts 2•-7•. DSC diagrams for radical adducts 2•-7•
(Figures S19-S24). Details of computational methods, Cartesian
coordinates, computed total energy of optimized structure of radical
adduct 1•. 1H NMR (Figures S25-S30) and infrared spectra (Figures
S31-S42) for new diamagnetic compounds 2-7 and infrared
spectra for 2•-7•. This material is available free of charge via the
Internet at http://pubs.acs.org.
JO0708846
7532 J. Org. Chem., Vol. 72, No. 20, 2007