Kinetic Analysis for the Effect of Intramolecular Hydrogen Bonding on Photophysical Properties of<i>N</i>-Hydroxyalkyl-1,8-naphthalimides
作者:Kazuhiko Matsubayashi、Chisato Kajimura、Hideo Shiratori、Yasuo Kubo、Toshitada Yoshihara、Seiji Tobita
DOI:10.1246/bcsj.20090330
日期:2010.9.15
N-Methyl-, N-(2-hydroxyethyl)-, N-(2-methoxyethyl)-, N-(3-hydroxypropyl)-, and N-(3-methoxypropyl)-1,8-naphthalimide (1, 2a, 2b, 3a, and 3b, respectively) were prepared and their photophysical properties examined. The UV and IR spectra of 2a and 3a in dichloromethane showed the presence of intramolecular hydrogen bonding between the carbonyl group and the hydroxy group. In addition, the fluorescence intensities of 2a and 3a in dichloromethane were found to be about two times larger than those of 1, 2b, and 3b. Furthermore, the fluorescence lifetimes of 2a and 3a, determined by picosecond single photon counting, were about two times longer than those of 1, 2b, and 3b. The rate constants of the intersystem crossing (kisc) for 2a and 3a, calculated based on the quantum yields of the intersystem crossing (Φisc) determined by the time-resolved thermal lensing technique, were about one half of those obtained for 1, 2b, and 3b, while the rate constants of fluorescence emission (kf) and internal conversion (kic) were minimally affected by the presence of intramolecular hydrogen bonding. Enhancement of the fluorescence quantum yield and the lifetime of 2a and 3a was thus explained by a decrease in the efficiency of the intersystem crossing from 1(ππ*) to 3(nπ*), that results from an increase in the energy of the 3(nπ*) level due to the presence of intramolecular hydrogen bonding.
合成了 N-甲基、N-(2-羟乙基)、N-(2-甲氧基乙基)、N-(3-羟丙基) 和 N-(3-甲氧基丙基)-1,8-萘酰亚胺 (分别为 1、2a、2b、3a 和 3b),并考察了它们的光物理性质。2a和3a在二氯甲烷中的紫外和红外光谱显示了羰基和羟基之间的分子内氢键的存在。此外,2a和3a在二氯甲烷中的荧光强度大约是1、2b和3b的两倍。此外,利用皮秒单光子计数法测定的2a和3a的荧光寿命大约是1、2b和3b的两倍。根据时间分辨热透镜技术测定的系间窜越量子产率(Φisc)计算得出,2a和3a的系间窜越速率常数(kisc)约为1、2b和3b的一半,而荧光发射速率常数(kf)和内转换速率常数(kic)则基本不受分子内氢键的影响。因此,2a和3a的荧光量子产率和寿命的增强可归因于从1(ππ*)到3(nπ*)的系间窜越效率的降低,这是由于分子内氢键的存在导致3(nπ*)能级的能量增加所致。