Synthesis, oxidation and photophysical properties of novel derivatives of acyclic aromatic amines

Article abstract of DOI:10.1135/cccc20071255

Conjugated acyclic arylamine derivatives, N-(4-methylphenyl)-N-(2-methyl-1- phenylpropyl)amine and N-(4-methoxyphenyl)-N-(2-methyl-1-phenylpropyl)amine, have been synthesized and characterized. Their photophysical properties have been investigated in polar methanol and non-polar cyclohexane solutions, and in PS and PMMA polymer matrices. The influence of the environment polarity as well as of the substituent in para-position of the aryl on the absorption, emission spectra and the fluorescence quantum yield has been studied. In the absorption and emission spectra, the observed absorption and emission band maxima were red shifted and the observed quantum yield was higher in the polar solution in comparison with the non-polar solution or polymer matrices. The distance of short- and long-wavelength absorption maxima in the methoxy derivative was larger and the emission band was red shifted in comparison with the methyl derivative. Chemical and photochemical oxidation of the prepared amines gives unstable nitroxides. High intramolecular quenching was observed in polymer matrix after photochemical oxidation of the amines.

Full text of DOI:10.1135/cccc20071255

Novel Derivatives of Acyclic Aromatic Amines
1255
SYNTHESIS, OXIDATION AND PHOTOPHYSICAL PROPERTIES
OF NOVEL DERIVATIVES OF ACYCLIC AROMATIC AMINES
Csaba KÓSA , Jaroslav MOSNÁČEK *, Adela BÍLEŠOVÁ , Peter KASÁKa4,b,
a1
a2,
a3
a5
a6
a7
Juraj KRONEK , Martin DANKO and Jozef KOLLÁR
a
Polymer Institute, Slovak Academy of Sciences, Dúbravska cesta 9, 842 36 Bratislava,
Slovak Republic; e-mail: upolkosa@savba.sk, upolmosj@savba.sk, upolbila@savba.sk,
upolgazo@savba.sk, upolkron@savba.sk, upoldan@savba.sk, upoljkol@savba.sk
Department of Organic Chemistry, Faculty of Natural Sciences, Comenius University,
42 15 Bratislava, Slovak Republic
1
2
3
4
5
6
7
b
8
Received Decem ber 14, 2006
Accepted Jun e 26, 2007
Con jugated acyclic arylam in e derivatives, N-(4-m eth ylph en yl)-N-(2-m eth yl-1-ph en yl-
propyl)am in e an d N-(4-m eth oxyph en yl)-N-(2-m eth yl-1-ph en ylpropyl)am in e, h ave been syn -
th esized an d ch aracterized. Th eir ph otoph ysical properties h ave been in vestigated in polar
m eth an ol an d n on -polar cycloh exan e solution s, an d in PS an d PMMA polym er m atrices.
Th e in fluen ce of th e en viron m en t polarity as well as of th e substituen t in para-position of
th e aryl on th e absorption , em ission spectra an d th e fluorescen ce quan tum yield h as been
studied. In th e absorption an d em ission spectra, th e observed absorption an d em ission ban d
m axim a were red sh ifted an d th e observed quan tum yield was h igh er in th e polar solution
in com parison with th e n on -polar solution or polym er m atrices. Th e distan ce of sh ort- an d
lon g-wavelen gth absorption m axim a in th e m eth oxy derivative was larger an d th e em ission
ban d was red sh ifted in com parison with th e m eth yl derivative. Ch em ical an d ph otoch em i-
cal oxidation of th e prepared am in es gives un stable n itroxides. High in tram olecular quen ch -
in g was observed in polym er m atrix after ph otoch em ical oxidation of th e am in es.
Keyw ord s: Am in es; Nitroxides; Oxidation s; Ph otoch em istry; Fluorescen ce spectroscopy.
Free n itroxyl radicals are of great im portan ce for several reason s. Th ey play
an im portan t role in th e m ech an ism of ligh t an d partially h eat stabilization
of polyolefin s. In th is case, stable free n itroxyl radicals are form ed from
1
th eir precursors – sterically h in dered am in es (HAS) – durin g stabilization .
Th e free n itroxyl radical can in fluen ce ph otoch em ical an d ph otoph ysical
processes due to its param agn etic effect. In term olecular quen ch in g of ex-
cited sin glet an d triplet states of probes was observed in th e presen ce of free
2
n itroxyl radicals . In th e n in eties, a specific group of probes with n itroxyl
3
–6
radical boun ded in th e m olecule h as been syn th esized an d in vestigated
.
Th e form ation or decay of th e free radical, followed by ESR m easurem en ts,
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1255–1268
©
2007 Institute of Organic Chemistry and Biochemistry
doi:10.1135/cccc20071255

1
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Kósa et al.:
is associated with on /off switch in g of th e ch rom oph ore em ission as a result
of in tram olecular quen ch in g. Gen erally, th e efficien cy of in tram olecular
quen ch in g in th ese probes depen ds on th e size of th e lin ker, wh ich con -
3
–6
n ects th e ch rom oph ore with radical cen ter, an d on th e m edium
.
In recen t years, an in ten sive study of free n itroxyl radicals was prom pted
by th e n ew polym erization m eth od, livin g free radical polym erization
(
LFRP). Th is tech n ique offers th e con trol of m olecular weigh t an d m olecu-
lar weigh t distribution (polydispersity) in th e radical polym erization as well
7
,8
as a possibility of preparation of polym ers with required design . In m ost
cases, 2,2,6,6-tetram eth ylpiperidin e-1-oxide (TEMPO) is used in com bin a-
tion with peroxide as a polym erization in itiator9 . Its >N–O–R form can
be used as un im olecular in itiator with out usin g peroxides. However, som e
problem s are still to be overcom e. For exam ple, applicable m on om ers are
lim ited m ain ly to styren e derivatives. High polym erization tem peratures
–12
(
above 110 °C) are required for polym erization . To overcom e th ese prob-
lem s, differen t structures of n itroxyl radicals an d/or its >N–O–R form were
1
3–15
studied
. Com m on m eth od of preparation of th ese in itiators is from ap-
propriate h in dered am in es.
In our approach , we in ten d to study ph otoph ysical properties of two n ew
arom atic am in es. At th e sam e tim e, a study of ch em ical an d/or ph otoch e-
m ical oxidation to n itroxides was plan n ed. Due to direct con jugation of th e
arom atic rin g with th e free electron pair of n itrogen , a m arked in tra-
m olecular quen ch in g of fluorescen ce could be ach ieved.
EXPERIMENTAL
Measurem en ts
Film s were prepared by castin g from ch loroform solution s (1 m l con tain in g 1 m g of am in e
an d 20 m g of polym er) on 2.5 × 4 cm glass plates. Th e plates were covered with a Petri dish
to slow solven t evaporation . Th is procedure resulted in film s with good optical quality. After
separation of film s from glass plates by dippin g in to distilled water, th e film s were dried
un der vacuum to rem ove residual solven t.
For irradiation , a m edium pressure m ercury arc in a Spectram at apparatus (Ivoclar A.G.,
Sch aan , Liech ten stein ) with th e wh ole spectrum was used.
NMR spectra (δ, ppm ; J, Hz) were recorded on a Varian 300 MHz spectrom eter (Varian ,
Germ an y). UV spectra were recorded on
Sh im adzu, Japan ). Steady-state em ission spectra were recorded on a Perkin –Elm er MPF4
spectrofluorim eter (Perkin –Elm er, Norfolk (CT), U.S.A.), wh ich was con n ected th rough in ter-
a Sh im adzu UV1650PC spectroph otom eter
(
1
9
face an d A/D con verter to a m icrocom puter for data collection . Em ission of solution s was
m easured at th e righ t an gle in a 1 × 1 cm cell. Solution s were deaerated by bubblin g with
argon for 10 m in im m ediately before m easurin g. Th e em ission spectra of doped polym er film s
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1255–1268

Novel Derivatives of Acyclic Aromatic Amines
1257
were m easured in th e presen ce of air usin g a fron t-face arran gem en t in special sam ple
h older at 45°.
Th e quan tum yield of m eth an ol an d cycloh exan e solution s was determ in ed usin g an th ra-
cen e as stan dard an d assum in g its low sen sitivity to th e m edium . An th racen e was used as
stan dard owin g to its solubility an d com patibility with differen t m atrices used. For our pur-
pose, th is kin d of com parison was sufficien t. Th e quan tum yields were determ in ed accord-
in g to Eq. (1)
∞
AS
A
IF (v)dv



1 – 10
10



S
∫
∫
0
∞
ΦF = ΦF
(1)
S
1 −
IF
(
v
)d
v
0
S
wh ere ΦF is th e quan tum yield of an th racen e as a stan dard, wh ich was assum ed to be 0.25
2
0
S
F
for all en viron m en ts . For relative quan tum yield, th e value of Φ for an th racen e was set at 1.
∞
∞
S
In tegrals
IF (v)dv an d
I (v)dv are th e areas un der em ission curves of th e probe an d stan -
dard, respectively, A an d A are absorption s of th e probe an d stan dard at th e excitation
∫
0
∫
0
F
S
wavelen gth . An th racen e was excited at 356 n m .
Ch em icals
Ben zaldeh yde, 4-m eth ylan ilin e, 4-m eth oxyan ilin e, isopropylm agn esium ch loride (2 M eth er
solution , Aldrich ), Sc(OTf)3 (Fluka), eth yl acetate (Ch em apol), 70% meta-ch loroperoxy-
ben zoic acid (m CPBA, Aldrich ), Na CO (Slavus, Bratislava), Na SO (Mikroch em , Bratislava),
2
3
2
4
CaH2 (Lach em a, Prah a) an d isoh exan e (Hexol, Slovn aft) were used as received. Eth an ol
Cen tralch em , Bratislava) was redistilled for th e syn th esis of im in es an d used as received for
(
crystallization s. Toluen e (Cen tralch em , Bratislava) for reaction s un der an h ydrous con dition s
was distilled from sodium , but for extraction it was used as received. Dich lorom eth an e
(
Slavus, Bratislava) was dried over CaH2.
Syn th esis
Th e studied com poun ds were syn th esized usin g m ultistep reaction s accordin g to Sch em e 1.
O
H
EtOH
reflux
C
+
H2N
H3C
R
CH N
R
CH3
CH
CH NH
H3C
CH3
CH
CH
i-PrMgCl
Sc(OTf)3
m-CPBA
R
N
O
R
or hν
unstable
3, R = CH3
4, R = OCH3
decomposition
SCHEME 1
Syn th esis of am in es 3 an d 4 an d th e respective n itroxides
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Kósa et al.:
N-(4-Methylphenyl)-N-(1-phenylmethylidene)amine (1)
Com poun d 1 was syn th esized accordin g to th e publish ed procedure16. Ben zaldeh yde (10.6 g,
0
.1 m ol) was added to th e solution of p-toluidin e (10.7 g, 0.1 m ol) in eth an ol (50 m l). Th e
reaction m ixture was refluxed for 30 m in an d th e solven t was evaporated. Th e residue was
purified by distillin g off th e un reacted ben zaldeh yde an d crystallization from eth an ol. Th e
product was obtain ed in 61% yield as yellow crystals, m .p. 27–29 °C (ref.16 30–32 °C). H NMR
1
(
300 MHz, CDCl ): 8.38 (s, 1 H, CH); 7.84 (m , 2 H, HAr); 7.39 (m , 3 H, HAr); 7.13 (m , 4 H,
3
1
3
HAr); 2.31 (s, 3 H, -CH ). C NMR (75 MHz, CDCl ): 159.3 (CH=N); 149.3 (CAr-N); 136.2
3
3
(
CAr); 135.6 (CAr); 131.1 (CArH); 129.6 (2 × CArH);128.6 (4 × CArH); 120.7 (2 × CArH); 20.9 (-CH3).
N-(4-Methoxyphenyl)-N-(1-phenylmethylidene)amine (2)
Com poun d 2 was syn th esized sim ilarly to com poun d 1 16. Th e crude product was filtered off
an d recrystallized from eth an ol. Th e gray plates of pure product were obtain ed in 74% yield,
1
6
1
m .p. 69.5–71 °C (ref. 69–70 °C). H NMR (300 MHz, CDCl ): 8.47 (s, 1 H, CH); 7.88 (m ,
3
1
H, HAr); 7.87 (m , 1 H, HAr); 7.45 (m , 3 H, HAr); 7.23 (ddd, 2 H, J = 8.7, 6.6, 2.4, HAr); 6.92
1
3
(
(
ddd, 2 H, J = 8.7, 6.6, 2.4, HAr); 3.01 (s, 3 H, -OCH ). C NMR (75 MHz, CDCl ): 158.4
3 3
CH=N); 158.2 (CAr-N); 144.8 (CAr); 136.3 (CAr); 131.0 (CArH); 128.7 (2 × CArH); 128.5 (2 ×
CArH); 122.1 (2 × CArH); 114.3 (2 × CArH); 55.4 (-OCH ).
3
N-(4-Methylphenyl)-N-(2-methyl-1-phenylpropyl)amine (3)
Com poun d 3 was syn th esized accordin g to th e publish ed procedure17,18. To a solution of
com poun d 1 (0.2 g, 1 m m ol) in dry toluen e (1 m l) was added Sc(OTf)3 (0.49 g, 0.1 m m ol)
an d th en isopropylm agn esium ch loride (0.2 g, 2 m m ol) dropwise at –5 °C. Th e reaction m ix-
ture was stirred at room tem perature for 5 h in Ar atm osph ere an d th en th e reaction was
stopped with aqueous solution of am m on ium ch loride. Th e m ixture was extracted with tolu-
en e, dried over an h ydrous sodium sulfate an d th e solven t was evaporated un der vacuum . Af-
ter purification by silica colum n ch rom atograph y usin g toluen e as an eluen t, a h igh ly
1
viscous yellow liquid was obtain ed in 84% yield. H NMR (300 MHz, CDCl ): 7.27 (d, 4 H,
3
J = 4.2, HAr); 7.19 (m , 1 H, J = 4.2, HAr); 6.86 (d, 2 H, J = 8.0, HAr); 6.41 (d, 2 H, J = 8.0, HAr);
4
6
.08 (d, 1 H, J = 6.0, CH-N); 3.97 (bs, 1 H, NH); 2.15 (s, 3 H, -CH ); 2.01 (m , 1 H, J = 6.0,
3
1
3
.6, CH); 0.96 (d, 3 H, J = 6.6, -CH ); 0.90 (d, 3 H, J = 6.6, -CH ). C NMR (75 MHz,
3
3
CDCl ): 145.3 (CAr); 142.6 (CAr); 129.5 (2 × CArH); 128.1 (2 × CArH); 127.2 (2 × CArH); 126.7
3
(
(
2 × CArH); 126.2 (CAr); 113.4 (CArH); 64.1 (CH-N); 34.8 (CH); 20.3 (-CH ); 19.7 (-CH ); 18.6
3 3
-CH ). For C17H21N (239.4) calculated: 85.31% C, 8.84% H, 5.85% N; foun d: 85.31% C,
3
8
.85% H, 5.87% N. MS, m/z (rel.%): 239 (50), 196 (100), 180 (15), 118 (35), 91 (40), 77 (15).
N-(4-Methoxyphenyl)-N-(2-methyl-1-phenylpropyl)amine (4)
Com poun d 4 was syn th esized sim ilarly to com poun d 3, but on ly 0.05 m m ol (0.25 g) of
Sc(OTf)3 was added an d th e reaction tem perature was kept at –5 to 0 °C. A h igh ly viscous
1
yellow liquid was obtain ed in 88% yield. H NMR (300 MHz, CDCl ): 7.28 (d, 4 H, J = 4.5,
3
HAr); 7.21 (m , 1 H, J = 4.5, HAr); 6.66 (ddd, 2 H, J = 9.0, 3.6, 2.4, HAr); 6.44 (ddd, 2 H, J =
9
.0, 3.6, 2.4, HAr); 4.03 (d, 1 H, J = 6.0, CH-N); 3.85 (bs, 1 H, NH); 3.66 (s, 3 H, -OCH ); 2.01
3
1
3
(
(
m , 1 H, J = 6.0, 6.9, CH); 0.97 (d, 3 H, J = 6.9, -CH ); 0.90 (d, 3 H, J = 6.9, -CH ). C NMR
3 3
75 MHz, CDCl ): 151.8 (CAr-O); 142.9 (CAr); 142.2 (CAr); 128.3 (4 × CArH); 127.4 (2 × CArH);
3
1
1
26.8 (CArH); 114.9 (CArH); 114.5 (CArH); 64.8 (CH-N); 55.9 (-OCH ); 35.1 (CH); 19.8 (-CH );
3 3
8.8 (-CH ). For C17H21NO (255.4) calculated: 79.96% C, 8.29% H, 5.49% N; foun d: 79.38% C,
3
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1255–1268

Novel Derivatives of Acyclic Aromatic Amines
1259
8
7
.37% H, 5.29% N. MS, m/z (rel.%): 255 (50), 212 (100), 197 (23), 168 (37), 134 (30), 91 (35),
7 (15).
Oxidation of Amine 3
To a solution of am in e 3 (0.2 g, 0.84 m m ol) in dry CH Cl (1 m l), a solution of m CPBA
2
2
(
2 equiv., 0.41 g, 2.38 m m ol) in dry CH Cl (2 m l) was added at 0 °C. Th e reaction m ixture
2 2
was stirred at room tem perature un der argon atm osph ere for 12 h . Th e reaction m ixture
was extracted 4 tim es with a saturated solution of sodium carbon ate. Organ ic ph ase was
dried over an h ydrous sodium sulfate an d th e solven t was evaporated. Th e presen ce of
n itroxide derivatives was proved by ESR m easurem en ts (Fig. 1). However, th e prepared
n itroxides were un stable as described below. Decom position products were n ot ch aracterized.
Oxidation of Amine 4
Com poun d 4 (0.3 g, 1.17 m m ol) was oxidized sim ilarly as described above. After purifica-
tion by colum n ch rom atograph y usin g h exan e/eth yl acetate (10:1) as an eluen t, isopropyl
ph en yl keton e (33%) an d bis(4-m eth oxyph en yl)diazen eoxide (30%) as a m ajor decom posi-
tion products were obtain ed.
1
Isopropyl phenyl ketone. H NMR (300 MHz, CDCl ): 7.97 (dd, 2 H, J = 6.9, 1.8, HAr); 7.55
3
(
m , 1 H, HAr); 7.46 (ddd, 2 H, J = 6.9, 7.8, 1.8, HAr); 3.56 (m , 1 H, J = 6.9, CH); 1.22 (d, 6 H,
J = 6.9, 2 × CH ). MS, m/z (rel.%): 148 (8), 105 (100), 77 (37), 51 (14), 27 (4).
3
1
Bis(4-methoxyphenyl)diazeneoxide. H NMR (300 MHz, CDCl ): 8.27 (m , 4 H, HAr); 6.98 (m ,
3
4
H, HAr); 3.89 (s, 3 H, OCH ); 3.88 (s, 3 H, OCH ). MS, m/z (rel.%): 258 (100), 121 (52), 107
3 3
(
43), 92 (20), 77 (25), 64 (15).
FIG. 1
ESR spectra of th e reaction m ixture after oxidation of am in e 3 with m CPBA in toluen e (c =
–
2
1
× 10 m ol/l)
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Kósa et al.:
RESULTS AND DISCUSSION
Synthesis
Am in es 3 an d 4 were obtain ed in h igh yields an d purity by n ucleoph ilic ad-
dition of isopropylm agn esium ch loride usin g Sc(OTf) as a catalyst in dry
3
toluen e an d in ert atm osph ere. Th e catalyst Sc(OTf)3 is very h ygroscopic;
th e presen ce of water can decrease th e reaction yield even below 30%. Half
am oun t of Sc(OTf) was sufficien t for preparation of th e m eth oxy derivative
3
in com pared th e m eth yl derivative because of its h igh er reactivity. In both
cases, an excess of organ om agn esium ch loride is n eeded. Actually, on ly h alf
of th e available R groups are usually used in th e addition of an RMgX to
1
7
aldim in es .
Both am in es 3 an d 4 were oxidized in dry CH Cl with m CPBA (2 equiv.).
2
2
After work up of th e crude reaction m ixture, brown oil was obtain ed. Th e
presen ce of n itroxyl radicals in th e m ixture was determ in ed by EPR
spectroscopy (Fig. 1). However, purification by colum n ch rom atograph y on
silica gel or alum in a led to decom position . Sim ilarly, EPR spectroscopy sh ows
decom position of th e n itroxides in crude product m ixture durin g its
storin g. Th is in stability can be caused by th e presen ce of h ydrogen on th e
2
1,22
α-carbon to n itrogen
.
Th e decom position products form ed after oxidation of am in e 4 an d sepa-
rated by colum n ch rom atograph y usin g h exan e/eth yl acetate (10:1) as an
1
eluen t, were iden tified by H NMR an d m ass spectroscopy. Th ey were foun d
to be isopropyl ph en yl keton e an d bis(4-m eth oxyph en yl)diazen eoxide
(
Sch em e 2). Beside th e decom position products, startin g am in e was also re-
covered. Decom position products form ed after oxidation of am in e 3 were
n ot separated, but on th e base of TLC sim ilar decom position products as for
am in e 4 are expected.
O
H3C
O
O
N
CH3
N
O
H3C
CH3
SCHEME 2
Isopropyl ph en yl keton e an d bis(4-m eth oxyph en yl)diazen eoxide, th e respective decom posi-
tion products after am in e 4 oxidation
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1255–1268

Novel Derivatives of Acyclic Aromatic Amines
1261
Absorption and Emission Spectra of 3 and 4
Absorption spectra of am in es 3 an d 4 in m eth an ol an d cycloh exan e
solutions as well as in PS and PMMA polym er m atrices are shown in Figs 2
and 3, respectively. Th e spectra exh ibit two m axim a in both solven ts an d
polym er m atrices. Th e in fluen ce of en viron m en t polarity an d th e
substituen t in para-position of th e an ilin e rin g on th e absorption spectra
was observed. Th e sh ort-wavelen gth ban ds of th e m eth oxy derivative are
blue sh ifted com pared with th e m eth yl derivative. On th e oth er h an d, th e
lon g-wavelen gth ban ds of th e m eth oxy derivative are sh ifted to h igh er
wavelen gth s (red sh ift) com pared with th e m eth yl derivative. Th e tren d is
th e sam e in both solven ts an d polym er m atrices (Tables I an d II). Com pari-
son of th e absorption spectra of solution s in polar m eth an ol an d n on -polar
cycloh exan e sh ows a sligh t red sh ift of th e spectra for both com poun ds in
m eth an ol solution (Table I, Fig. 2). Sim ilarly, in m ore polar PMMA m atrix
th e UV absorption spectra of both com poun ds are red sh ifted com pared
with th e spectra observed in less polar PS m atrix (Table II, Fig. 3).
Th e em ission spectra of th e studied com poun ds were in vestigated in
deaerated m eth an ol an d cycloh exan e solution s an d in th e presen ce of air in
PMMA an d PS m atrices. For excitation , ligh t with th e wavelen gth equal to
th e lon gest absorption ban d of th e respective probe was selected. Th e rela-
FIG. 2
–
4
UV absorption spectra of am in es 3 an d 4 in m eth an ol an d cycloh exan e solution s (c = 1 × 10
m ol/l)
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1255–1268

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Kósa et al.:
tive quan tum yield was calculated from th e in tegrated observed em ission
spectra usin g an th racen e as a stan dard. Th e em ission ban d m axim a an d rela-
tive quan tum yields are presen ted in Figs 4, 5 an d Tables I, II. As sh own in
th e observed em ission spectra (Fig. 4) an d Table I, th e am in e em ission is
stron gly in fluen ced by th e substituen t in para-position of an ilin e rin g as
well as by en viron m en t polarity. Th e em ission spectrum of th e m eth oxy
derivative is red sh ifted com pared with th e m eth yl derivative in both sol-
ven ts (Fig. 4, Table I). An in crease in solven t polarity leads to th e sh ift of
th e em ission ban d m axim um to h igh er wavelen gth s (Fig. 4, Table I). A sim i-
lar in fluen ce on em ission spectra of th e am in e derivatives by m atrix polar-
TABLE I
Absorption an d em ission ch aracteristics of am in es 3 an d 4 in solution s
Meth an ol
Cycloh exan e
Am in e
λabs, n m
λem , n m
Φrel
λabs, n m
λem , n m
Φrel
3
4
250; 304.5
246.5; 315
355
371
0.4
247; 302
337
355
0.2
0.65
244; 313.5
0.55
FIG. 3
Lon ger UV absorption ban ds of am in es 3 an d 4 in PS an d PMMA m atrices (c = 1 m g/20 m g
polym er)
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Novel Derivatives of Acyclic Aromatic Amines
1263
ity an d substituen t was observed in PS an d PMMA m atrices. Th e em ission
spectrum of th e m eth oxy derivative is red sh ifted com pared with th e m eth yl
derivative in both polym er m atrices (Fig. 5, Table II) an d th e ban d m axi-
m um is m ore red sh ifted in m ore polar PMMA in com parison with th e PS
m atrix. In th e case of m eth yl derivative in th e PS m atrix, th e lon gest ab-
sorption ban d an d th e em ission ban d partially overlap.
Th e fluorescen ce quan tum yields of am in e derivatives were calculated ac-
cordin g to Eq. (1) relative to an th racen e as a stan dard. Th e results in dicate
th e in fluen ce of th e en viron m en t polarity as well as th e substituen t ch arac-
ter (Tables I an d II). As it can be seen from th e results (Table I), a sligh tly
TABLE II
Absorption an d em ission ch aracteristics of am in es 3 an d 4 in polym er m atrices
PS
PMMA
Am in e
λabs, n m
λem , n m
Φrel
λabs, n m
λem , n m
Φrel
3
4
240.5; 305.5
238.5; 317.5
333
362
<0.01
0.04
251; 306.5
247.5; 318
336
366
0.05
0.06
FIG. 4
Em ission spectra of am in es 3 an d 4 in deaerated m eth an ol an d cycloh exan e solution s (c =
–
5
1
× 10 m ol/l)
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Kósa et al.:
h igh er fluorescen ce quan tum yield was observed for both am in es 3 an d 4 in
m eth an ol th an in cycloh exan e. Ch an gin g of m eth yl group in para-position
of th e an ilin e rin g for th e m eth oxy group leads to an in crease in th e quan -
tum yield in both solven ts. Th e effect of th e substituen ts sh ows th e sam e
ten den cy in polym er m atrices as in solution s; h owever, th e quan tum yields
are about ten tim es lower th an in solution (Table II). Even th ough th e em is-
sion spectra in polym er m atrices were m easured in th e presen ce of air, th e
explan ation of lower quan tum yields in com parison with th e solution
caused on ly by efficien t fluorescen ce quen ch in g by oxygen absorbed in th e
polym er m atrix does n ot seem satisfactory. Oxygen con cen tration as well
as m obility in th e polym er m atrix is m u ch lower th an in solu tion . Th us,
an oth er possible explan ation could be th e form ation of n itroxides durin g
irradiation of th e polym er m atrices in air. Th e form ed peroxides could
cause very efficien t in tram olecular quen ch in g due to direct con jugation
with th e arom atic system . Durin g excitation with m on och rom atic ligh t in
spectrofluorim eter, a ch an ge in color of th e m easured polym er film from
colorless to red was observed. EPR spectra m easured after th is color ch an ge
of PS film con tain in g am in e 4 sh owed th e presen ce of n itroxyl radicals.
Com parin g th e polym er m atrices, lower quan tum yields were observed in
th e less polar PS m atrix th an in polar PMMA. In th e case of m eth yl deriva-
tive m easured in PS, th e calculated quan tum yield is stron gly in fluen ced
also by a large overlap of lon gest-wave absorption an d em ission ban ds.
FIG. 5
Em ission spectra of am in es 3 an d 4 in PS an d PMMA m atrices (c = 1 m g/20 m g polym er)
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Novel Derivatives of Acyclic Aromatic Amines
1265
Irradiation of Amine 4
As already m en tion ed above, th e n itroxides form ation was detected after
irradiation of am in e 4 in th e polym er film with m on och rom atic ligh t in
spectrofluorim eter. Th at is wh y we decided to follow th e ch an ges in UV-VIS
an d FT IR spectra of am in e 4 in th e PS m atrix at various irradiation tim es.
As sh own in Fig. 6, th e form ation of a sm all absorption ban d with m axi-
m um at 505 n m was observed durin g irradiation with wh ole th e spectrum
of a m edium -pressure m ercury arc. We assum e th is ban d could belon g to
th e form ed arom atic n itroxides.
No sign ifican t ch an ges, wh ich could in dicate decom position of arom atic
structure of th e studied com poun d, were observed in th e area below 350 n m
in absorption spectra. Th e con tin ued irradiation gave just very sm all
ch an ges in th e absorption m axim um at 505 n m , accom pan ied by an in -
crease in absorption in th e area from 370 to 450 n m , in dicatin g som e fast
con secutive reaction s of th e form ed n itroxides. UV absorption spectra of
th e dark reaction m ixtures of th e form ed n itroxides are depicted in Fig. 7.
We can see a slow decrease in th e absorption m axim um at 505 n m accom -
pan ied by an in crease in absorban ce below 450 n m . No sign ifican t ch an ge
was observed in th e absorption m axim um of th e studied com poun d in th e
area below 350 n m . Th is can in dicate th at durin g th e dark reaction th e
FIG. 6
UV-VIS spectra of am in e 4 in PS film irradiated at am bien t tem perature in air for differen t tim e
periods (c = 1 m g/20 m g polym er)
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form ed n itroxides slowly react with polym er m atrix. Th e reaction can be
m uch faster durin g irradiation in air, wh ere various radicals from PS can be
form ed th at can react with th e form ed n itroxides.
For com parison , an UV spectrum of am in e 4 in PS irradiated with m on o-
ch rom atic ligh t in spectrofluorim eter is given , in wh ich th e presen ce of
n itroxides was proved by EPR. As we can see, th e sam e absorption m axi-
m um at 505 n m is observed in th is spectrum .
In FT IR spectra th e on ly ch an ge in th e area of am in e ban ds at 3424 cm –1
was observed. Th us a sligh t decrease in absorban ce after 40-m in irradiation
of am in e 4 in PS film an d alm ost com plete disappearan ce of th e peak after
2
0-m in irradiation with m on och rom atic ligh t in spectrofluorim eter was
observed.
FIG. 7
UV-VIS spectra at differen t tim es of th e dark reaction of PS film con tan in g pre-irradiated
am in e 4 or irradiated with m on och rom atic ligh t (c = 1 m g/20 m g polym er)
CONCLUSIONS
Acyclic arylam in e derivatives, 3 an d 4, h ave been syn th esized in good
yields an d purity. Ph otoph ysical properties of th e am in es were studied in
polar m eth an ol an d n on -polar cycloh exan e solution s as well as in PS an d
PMMA m atrices. Th eir spectral ch aracteristics are in fluen ced by polarity as
well as by th e ch aracter of th e substituen t in para-position of th e an ilin e
rin g. Th e com poun ds exh ibit th e two absorption m axim a, wh ich are
sh ifted in depen den ce on th e en viron m en t polarity an d type of th e
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Novel Derivatives of Acyclic Aromatic Amines
1267
substituen t. Fluorescen ce of both am in es is red sh ifted in m eth an ol an d
PMMA m atrix.
Ch em ical oxidation of am in es 3 an d 4 gave th e respective un stable
n itroxides, wh ich decom pose durin g purification an d storage.
Ph otoch em ical oxidation of th e am in es was observed in polym er m atrices.
Th e form ed n itroxides dram atically decrease th e fluorescen ce quan tum
yields of th e studied am in es by in tram olecular quen ch in g in polym er m atrix
com pared with solution s. Preparation of m ore stable am in e derivatives with
alkyls in th e α-position to n itrogen can give n itroxides with switch in g
on /off th e ch rom oph ore em ission as a con sequen ce of h igh in tram olecular
quen ch in g.
The authors thank APVT grant agency for the financial support of this work through project
No. 51-004904. NMR measurements provided by the Slovak State Programme Project No.
2
003SP200280203 are gratefully acknowledged as well.
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