Solvent and substituent effects on the fluorescent properties of coelenteramide analogues
作者:Ryota Saito、Takashi Hirano、Haruki Niwa、Mamoru Ohashi
DOI:10.1039/a701156c
日期:——
Coelenteramide 1 is the light emitter in aequorin
bioluminescence. To
establish the fluorescent character of 1, the fluorescence properties of
1 and a series of its analogues, 3a–f, possessing a substituent R
[= CF3, F, H, OCH3, OH,
N(CH3)2] at the para-position on the
5-phenyl group have been investigated in solvents of various polarity.
The fluorescence emission maxima of 1 and 3d–f, possessing an
electron-donating group R [= OCH3, OH,
N(CH3)2] shift to lower energy with increasing
solvent polarity, while those of the analogues 3a–c
(R = CF3, F, H) are independent of the solvent
polarity. The linear correlation between the fluorescence maxima of 1
and 3d–f and the solvent polarity scales can be explained by
formation of the singlet excited state with a charge-transfer (CT)
character. The quantum yields of CT fluorescence of 1 and 3d–f
have been found to be higher than those of 3a–c. These results
indicate that the solvatochromic fluorescence of 1 originates from the
CT excited state and the existence of an electron donating hydroxy group
on the 5-phenyl group is essential for determining a wavelength and a
high fluorescence quantum yield of aequorin bioluminescence.
腔肠素1是海萤素生物发光中的发光体。为了确定1的荧光特性,在各种极性的溶剂中研究了1及其一系列类似物3a-f的荧光特性,这些类似物在5-苯基基团的对位上具有取代基R(= CF3、F、H、OCH3、OH、N(CH3)2)。1和3d-f的荧光发射最大值具有电子供体基团R(= OCH3、OH、N(CH3)2),随着溶剂极性的增加,其最大值向较低能量移动,而类似物3a-c(R= CF3、F、H)的荧光发射最大值与溶剂极性无关。1和3d-f的荧光最大值与溶剂极性尺度之间的线性相关性可以用具有电荷转移(CT)特征的单线态激发态的形成来解释。1和3d-f的CT荧光量子产率高于3a-c。这些结果表明,1的溶剂致色荧光来自CT激发态,5-苯基基团上存在电子供体羟基对于确定海萤素生物发光的波长和高荧光量子产率至关重要。