Regioselective photoaddition of amine to styrylthiophenes
T. I. Ho,* C. S. Ho, S. M. Shin and K. Pa
Department of Chemistry,National Taiwan University,Taipei, Taiwan
The photochemistry of styrylthiophene(ST) and its derivatives with amines
is investigated. Exciplex emission for tertiary amines and 3-ST systems
have been observed. Photochemical addition of tertiary and secondary amines to
2-ST are non-regioselective. Photoaddition of ammonia to 2-ST sensitized
by dicyano benzene is regioselective. The difference in the photochemical
behaviour is compared.
The reductive fluorescence quenching of para-substituted trans-3-styrylthioplienes
[X=OCH3, CH3, CH(CH3)2, H, F, Cl, Br, CN] by tertiary amines (triethylamine
TEA, diisopropylmethylamine DIPEA, diisopropylmethylamine DIPMA) were studied.
Exciplexes emission are observed in non-polar solvents. Figure 1a shows
the fluorescence spectra of 3-styrylthiophenes and triethylamine (TEA)
exciplexes in n-hexane. Figure 1b shows the fluorescence spectra of
3-styrylthiophenes and diisopropylmethylamine (DIPMA) exciplexes in benzene.
Figure 1c shows the fluorescence spectra of 3-styrylthiophenes and
diisopropylethylamine (DIPEA) exciplexes in benzene. The data are summarized
in Table 1.
Table 1 Maximum emission of 3-(4'-X-)StT - amine exciplexes
in benzenea and n-hexaneb
|DIPEAa|| DIPMAa ||TEAb|
|3-(4'-X-)StT ||l(max) ||l(max)|| lmax |
|X=OCH3 ||414.5||- ||- |
|X=CH3|| 433.0 ||436.2 ||426.2 |
|X=CH(CH3)2 ||434.0 ||437.5 ||427.0 |
|X=H ||442.0 ||450.5 ||438.7 |
|X=F ||453.0 ||446.5 ||427.5 |
|X=Cl ||439.0 ||459.3 ||441.0 |
|X=Br ||499.2 ||- ||449.0 |
|X=CN ||2.48 ||436.2 ||480.0 |
Photochemical addition of tertiary amines
Amine adduct 3 : 4 ratio 1 : 1 nonregioselective
3 + 4 27% yield
Photochemical addition of secondary amines
7 : 8 = 4.5 : 1
10 : 11 = 3.7 : 1 (~5% yield)
Photochemical addition of ammonia
Nucleophilic addition of NH3 only occurs at 15.