No abstract

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.

A new and synthetically versatile strategy has been developed for the phosphorescence color tuning of cyclometalated iridium phosphors by simple tailoring of the phenyl ring of ppy (Hppy = 2‐phenylpyridine) with various main‐group moieties in [Ir(ppy‐X)2(acac)] (X = B(Mes)2, SiPh3, GePh3, NPh2, POPh2, OPh, SPh, SO2Ph). This can be achieved by shifting the charge‐transfer character from the pyridyl groups in some traditional iridium ppy‐type complexes to the electron‐withdrawing main‐group moieties and these assignments were supported by theoretical calculations. This new color tuning strategy in IrIII‐based triplet emitters using electron‐withdrawing main‐group moieties provides access to IrIII phosphors with improved electron injection/electron transporting features essential for highly efficient, color‐switchable organic light‐emitting diodes (OLEDs). The present work furnished OLED colors spanning from bluish‐green to red (505–609 nm) with high electroluminescence efficiencies which have great potential for application in multicolor displays. The maximum external quantum efficiency of 9.4%, luminance efficiency of 10.3 cd A−1 and power efficiency of 5.0 lm W−1 for the red OLED (X = B(Mes)2), 11.1%, 35.0 cd A−1, and 26.8 lm W−1 for the bluish‐green device (X = OPh), 10.3%, 36.9 cd A−1, and 28.6 lm W−1 for the bright green device (X = NPh2) as well as 10.7%, 35.1 cd A−1, and 23.1 lm W−1 for the yellow‐emitting device (X = SO2Ph) can be obtained.