Phenyl-substituted 2,2′:6′,2″-terpyridine as a new series of fluorescent compounds—their photophysical properties and fluorescence tuning
作者:Toshiki Mutai、Jin-Dong Cheon、Shinpei Arita、Koji Araki
DOI:10.1039/b102685m
日期:——
Several phenyl-substituted 2,2â²:6â²,2â³-terpyridines (tpy) were synthesized and it was found that 4â²-phenyl tpy (ptp, 3) exhibited the most effective fluorescence, whose quantum yield was up to 0.64 in cyclohexane. For further study on tuning the fluorescence properties of ptp, different substituents were introduced into the p-position of the phenyl group. While Br- 10, Cl- 11, and CH3-ptp 12 showed their absorption and fluorescence in the same region as 3, those of NH2- 14 and Me2N-ptp 15 were observed at much longer wavelengths. In addition, fluorescence maxima of 14 and 15 showed large (>130 nm) solvent dependence. The difference between ground and excited state dipole moment (Îμ) for 15 was estimated to be 15.2 D by the LippertâMataga equation, indicating the intramolecular charge transfer (ICT) process. Semi-empirical MO calculation (MOPAC/AM1) demonstrated that the HOMO-1, HOMO and LUMO of 3, 10â12 were mainly localized on the phenyl (Ïph), tpy (Ïtpy) and tpy (Ï*tpy) part, respectively, indicating that the lowest energy absorption band of 3, 10â12 was the local excitation (ÏtpyâÏ*tpy). In the
case of 14 and 15, which have an electron-donating substituent, Ïph instead of Ïtpy became the HOMO. Thus, the lowest energy absorption of 14 and 15 was an ICT transition (ÏphâÏ*tpy), and a large red shift of the fluorescence occurred. In these compounds, the energy level of Ïph is controlled without affecting that of Ïtpy and Ï*tpy, suggesting a novel approach for tuning the color of fluorescence.
合成了几种苯基取代的2,2':6',2''-三联吡啶(tpy),发现4'-苯基tpy(ptp,3)具有最有效的荧光,其在环己烷中的量子产率高达0.64。为了进一步研究调节ptp的荧光性质,将不同的取代基引入苯环的p位。Br-10,Cl-11和CH3-ptp 12显示与3相同的吸收和荧光区域,而NH2-14和Me2N-ptp 15的吸收和荧光则在更长的波长处被观察到。此外,14和15的荧光最大值显示了大于130 nm的溶剂依赖性。根据Lippert-Mataga方程,15的基态和激发态偶极矩差(Δμ)估计为15.2 D,表明存在分子内电荷转移(ICT)过程。半经验MO计算(MOPAC/AM1)表明,3、10-12的HOMO-1、HOMO和LUMO主要分别定域在苯基(πph)、tpy(πtpy)和tpy(π*tpy)部分,表明3、10-12的最低能量吸收带是局部激发(πtpy-π*tpy)。对于具有电子给体取代基的14和15,πph而非πtpy成为HOMO。因此,14和15的最低能量吸收是ICT跃迁(πph-π*tpy),并发生了大幅度的荧光红移。在这些化合物中,πph的能级可以在不影响πtpy和π*tpy能级的情况下进行调控,这为调节荧光颜色提供了一种新方法。