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

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.

Substitution of Metallocenes with [2.2]Paracyclophane to Enable Confocal Microscopy Imaging in Living Cells

“…The spectrum of 1 closely resembles those of other 1-pyrene derivatives with π-conjugated substituents, for example, 1-phenylethynylpyrene. [19] Thus, in analogy to previous reports, the low-est absorption band is assigned to a "pyrene-like" transition, similar to the strongly allowed S 2 ← S 0 transition in unsubstituted pyrene. This assignment is further supported by the results of TD-DFT calculations.…”

“…The elongation of the aromatic system increases the HOMO (π orbital) energy and lowers the LUMO (π* orbital) energy, and this leads to a substantial redshift of the HOMO-LUMO transition compared with that of pyrene, for which a similar HOMO-LUMO excitation gives rise to a band (S 2 ←S 0 ) at λ = 334 nm. [19] Information concerning the higher excited states of 1 is given in the Supporting Information. Compound 1 is strongly luminescent both in dilute solution and in a polymer film.…”

Regioselective Substitution at the 1,3- and 6,8-Positions of Pyrene for the Construction of Small Dipolar Molecules

“…17 Following this inspiration, the 1,3-diphenylpyrene (3) was successfully synthesized in 85 % yield from 7-tert-butyl-1,3-diphenylpyrene, which is a key step for building dipolar architectures along the Z-axis. 18 The detailed synthetic procedure is illustrated in Scheme 1. Further bromination of 3 afforded 1,3-dibromo-6,8-diphenylpyrene (4) in high yield (79 %).…”

An Electron‐Poor C64 Nanographene by Palladium‐Catalyzed Cascade C−C Bond Formation: One‐Pot Synthesis and Single‐Crystal Structure Analysis

“…The π‐extended PAH 1 displayed distinct absorption spectral features with remarkably high molar absorptivities in the visible range (Figure 3). Similar to other two‐dimensional PAH scaffolds, such as pyrenes,28 coronenes,13a or hexabenzocoronenes,29 the absorption spectrum of 1 is not dominated anymore by the lowest‐energy S 0 –S 1 transition ( λ max =584 nm, ɛ max =141 200  m −1  cm −1 ) but by a higher‐energy absorption band at λ max =489 nm, which is characterized by well‐resolved vibronic progressions and a very high molar extinction coefficient of 278 300  m −1  cm −1 . According to TD‐DFT calculations, the transition dipole moments of these two main transitions are aligned along the short and long molecular axes of the central pyrene core (Figure 3, right).…”