Poly(1,4-Naphthylene Sulfide) Oligomers: Electronic and Vibrational Spectra of the Pristine and Oxidized Forms
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N2+BF 4+
""Z-
DMSO, argon it., 2h
/
S
B&
Br I tool. equiv.
5 rotl equiv.
following an electron-transfer chain mechanism (SRN 1) [6,7]. A solution of crude 1-naphtha325 Mat. Res. Soc. Symp. Proc. Vol. 328. ©1994 Materials Research Society
lenediazonium tetrafluoroborate in DMSO is dropped into a solution of a five-fold excess of sodium 4-bromo-l-naphthalenethiolate in the same solvent at room temperature and under an atmosphere of argon. After 2 h the resulting suspension is poured into cold brine and the precipitate thereof filtered, washed with water and dried. After a 4-fold extraction with hot light petroleum (bp 80-100 0 C), chromatography on silica gel [petroleum ether (bp 4060 'C) and gradients with dichloromethane as eluants] furnished the previously unknown lad. Their structure is consistent with the 1H nmr spectrum (taken in CDCI 3 on a Varian GEMINI 200 spectrometer): 4-Bromo-l-naphthyl 1-naphthyl sulfide (la: n=l): yellow solid, mp 115.5-117 'C . lb (n=2), dark yellow solid, mp 185.6-186.6 'C. lc (n=3), orange solid, mp 90-110 0C. ld (n=4), orange/red waxy solid, mp 110-130 'C. Spectra were obtained by the following instruments: Perkin Elmer LAMBDA 9 (uv-visnir), Bruker IFS 66 (ir) and RS 100 (Raman, laser exc. 1064 nm). RESULTS AND DISCUSSION The electronic spectra of compounds la-d are shown in fig. 1. The very weak dependence of the absorption bands on the molecular weight shows that no appreciable conjugation among the aromatic units takes place, as in the case of PPS oligomers [8].
2.0
U o
.. V.N
400
300 nm
Figure 1. Electronic spectra for CH2 C12 solution of compounds: la (-), lb (-Ic Id (-.-)
(- -) and
Fig.2 shows the vibrational spectra of the same compounds, excluding the C-H stretching region. As expected from the complexity and low symmetry of these molecules, many bands are observed in both ir and Raman spectra. The strongest ir band is observed in the region of the C-H wag at about 760 cm-' and has no Raman correspondent band. The strongest Raman bands are observed between 1600 and 1300 cm-' where the ring stretching vibrations of naphthalene derivatives are expected [9]. A detailed analysis of these spectra cannot be developed here but some general points to note are: i) The spectra of la are characteristic of both the 1-monosubstituted (C 0 H7 -S) and 1,4disubstituted (S-C, 0 H6 -Br) naphthalene units which represent the terminal groups in the higher oligomers. On the other hand, the very similar spectra of lc and ld are mainly characteristic of the sulfur disubstituted central units (S-C,, H6 -S). This fact, for instance, is well shown by the fall in intensity of the ir and Raman active band at about 1060 cm-', which can be assigned to an aromatic-Br vibrational mode [10]. However, by passing from lb to lc some frequency change is observed for the ring stretch modes around 1560 and 1370 cm-' as well as in the region of the two adjacent H wag (800 cm-'). In our opinion, it is due to some
326
0a
0
cc
(U E C
M
1500
1250
1000
Wavenunber
750
om-1
500
250
Figur
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