Department of Chemistry, Durham University, South Road, Durham DH1 3LE, United Kingdom.
J Am Chem Soc. 2011 Aug 31;133(34):13349-62. doi: 10.1021/ja2006862. Epub 2011 Aug 5.
Pyrene derivatives substituted at the 2- and 2,7-positions are shown to display a set of photophysical properties different from those of derivatives substituted at the 1-position. It was found that, in the 2- and 2,7-derivatives, there was little influence on the S(2) ← S(0) excitation, which is described as "pyrene-like", and a strong influence on the S(1) ← S(0) excitation, which is described as "substituent-influenced". In contrast, the 1-substituted derivatives display a strong influence on both the S(1) ← S(0) and the S(2) ← S(0) excitations. These observations are rationalized by considering the nature of the orbitals involved in the transitions. The existence of a nodal plane passing through the 2- and 7-positions, perpendicular to the molecular plane in the HOMO and LUMO of pyrene, largely accounts for the different behavior of derivatives substituted at the 2- and 2,7-positions. Herein, we report the photophysical properties of a series of 2-R-pyrenes {R = C(3)H(6)CO(2)H (1), Bpin (2; pin = OCMe(2)CMe(2)O), OC(3)H(6)CO(2)H (3), O(CH(2))(12)Br (4), C≡CPh (5), C(6)H(4)-4-CO(2)Me (6), C(6)H(4)-4-B(Mes)(2) (7), B(Mes)(2) (8)} and 2,7-R(2)-pyrenes {R = Bpin (9), OH (10), C≡C(TMS) (11), C≡CPh (12), C≡C-C(6)H(4)-4-B(Mes)(2) (13), C≡C-C(6)H(4)-4-NMe(2) (14), C(6)H(4)-4-CO(2)C(8)H(17) (15), N(Ph)-C(6)H(4)-4-OMe (16)} whose syntheses are reported elsewhere. Furthermore, we compare their properties to those of several related 1-R-pyrene derivatives {R = C(3)H(6)CO(2)H (17), Bpin (18), C≡CPh (19), C(6)H(4)-4-B(Mes)(2) (20), B(Mes)(2) (21)}. For all derivatives, modest (0.19) to high (0.93) fluorescence quantum yields were observed. For the 2- and 2,7-derivatives, fluorescence lifetimes exceeding 16 ns were measured, with most being ca. 50-80 ns. The 4-(pyren-2-yl)butyric acid derivative (1) has a long fluorescence lifetime of 622 ns, significantly longer than that of the commercially available 4-(pyren-1-yl)butyric acid (17). In addition to measurements of absorption and emission spectra and fluorescence quantum yields and lifetimes, time-dependent density functional theory calculations using the B3LYP and CAM-B3LYP functionals were also performed. A comparison of experimental and theoretically calculated wavelengths shows that both functionals were able to reproduce the trend in wavelengths observed experimentally.
2- 和 2,7-位取代的芘衍生物显示出与 1-位取代衍生物不同的一组光物理性质。研究发现，在 2-和 2,7-衍生物中，对“芘样”的 S(2)←S(0)激发的影响很小，而对 S(1)←S(0)激发的影响很大，这被描述为“取代基影响”。相比之下，1-取代衍生物对 S(1)←S(0)和 S(2)←S(0)激发都有强烈的影响。这些观察结果可以通过考虑涉及跃迁的轨道的性质来合理化。在芘的 HOMO 和 LUMO 中，穿过 2-和 7-位并垂直于分子平面的节点平面的存在，在很大程度上解释了 2-和 2,7-位取代衍生物的不同行为。在此，我们报告了一系列 2-R-芘衍生物{ R = C(3)H(6)CO(2)H (1)，Bpin (2；pin = OCMe(2)CMe(2)O)，OC(3)H(6)CO(2)H (3)，O(CH(2))(12)Br (4)，C≡CPh (5)，C(6)H(4)-4-CO(2)Me (6)，C(6)H(4)-4-B(Mes)(2) (7)，B(Mes)(2) (8)}和 2,7-R(2)-芘衍生物{R = Bpin (9)，OH (10)，C≡C(TMS) (11)，C≡CPh (12)，C≡C-C(6)H(4)-4-B(Mes)(2) (13)，C≡C-C(6)H(4)-4-NMe(2) (14)，C(6)H(4)-4-CO(2)C(8)H(17) (15)，N(Ph)-C(6)H(4)-4-OMe (16)}的光物理性质，其合成方法在别处报道。此外，我们将它们的性质与几个相关的 1-R-芘衍生物{R = C(3)H(6)CO(2)H (17)，Bpin (18)，C≡CPh (19)，C(6)H(4)-4-B(Mes)(2) (20)，B(Mes)(2) (21)}进行了比较。对于所有衍生物，都观察到了适度（0.19）到高（0.93）的荧光量子产率。对于 2-和 2,7-衍生物，测量到超过 16 ns 的荧光寿命，大多数为 ca.50-80 ns。4-(芘-2-基)丁酸衍生物（1）具有 622 ns 的长荧光寿命，明显长于市售的 4-(芘-1-基)丁酸（17）。除了吸收和发射光谱以及荧光量子产率和寿命的测量外，还使用 B3LYP 和 CAM-B3LYP 函数进行了时间依赖密度泛函理论计算。实验和理论计算波长的比较表明，这两种功能都能够重现实验中观察到的波长趋势。
