Experimental and Theoretical Studies of the Photophysical Properties of 2- and 2,7-Functionalized Pyrene Derivatives

摘要

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_3H_6CO_2H(1), Bpin (2; pin = OCMe_2CMe_2O),OC_3H_6CO_2H (3), O(CH_2)_(12)Br (4), C≡CPh (5), C_6H_4-4-CO_2Me (6), C_6H_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_6H_4-4-B(Mes)_2 (13), C≡C-C_6H_4-4-NMe_2 (14), C_6H_4-4-CO_2C_8H_(17) (15), N(Ph)-C_6H_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_3H_6CO_2H (17), Bpin (18), C≡CPh (19), C_6H_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-l-yi)butyric add (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.