| Summary: | 碩士 === 國立中央大學 === 化學研究所 === 89 === The synthesis, structure, and photochemical behavior of the trans isomers of 4-(N-phenylamino)stilbene (1c), 4-(N-methyl-N-phenylamino)stilbene (1d), 4-(N,N-diphenylamino)stilbene (1e), and 4-(N-(2,6-dimethylphenyl) amino)stilbene (1f) are reported and compared to that of 4-aminostilbene (1a) and 4-N,N-dimethylaminostilbene (1b). The introduction of N-phenyl substituents to 4-aminostilbenes leads to a more planar geometry about the nitrogen atom, a red shift of the absorption and fluorescence spectra, and a less distorted central double bond and a larger charge-transfer character in the fluorescent state. Consequently, the N-phenyl derivatives 1c-1e have low photoisomerization quantum yields and high fluorescence quantum yields at room temperature, which is contrast to 1a, 1b, and any other previously reported unconstrained 4-monosubstituted trans-stilbenes. The isomerization of 1c and 1d is a singlet-state process, whereas it is a triplet-state process for 1e, presumably due to a higher singlet-state torsional barrier. The excited state behavior of 1f resembles 1a and 1b instead of 1c-1e as a consequence of the less planar amine geometry and weaker orbital interactions between the N-phenyl and the aminostilbene groups. Such an N-phenyl substituent effect is also found for 2 , 3 , 4 and 5 and appears to be general for other stilbenoid systems. The nature of this effect can be described as the “amino-conjugation effect”.
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