The effects of the introduction of an sp(2)-hybridized nitrogen atom (═N-) and thiophene ring on the structure geometries, frontier molecular orbital energies, and excited state energies related to singlet fission (SF) for some tetracene and pentacene derivatives were theoretically investigated by quantum chemical methods. The introduction of a nitrogen atom significantly decreases the energies of frontier molecular orbitals and hence improves their stabilities in air and light illumination. More importantly, it is helpful for reducing the energy loss of the exothermic singlet fission of pentacene derivatives. For fused benzene-thiophene structures, the (α, β) connection pattern could stabilize the frontier molecular orbitals, while the (β, β) connection pattern can promote the thermodynamic driving force of singlet fission. These facts provide a theoretical ground for rational design of SF materials.

A linear tetracene trimer linked by phenyl groups has been prepared for the first time. The triplet quantum yield formed via intramolecular singlet fission can reach up to 96% in this trimer, which is enhanced significantly compared with that in the dimer. This can be attributed to the stronger electronic coupling between tetracene subunits and more delocalized excitons in the trimer.

A covalently linked tetracene dimer has been prepared and its molecular structure is characterized by (1)H NMR and MALDI-TOF mass spectroscopy, and elemental analysis. The minimized molecular structure reveals that the tetracene subunits in a dimer adopt a "face-to-face" stacked configuration. Its absorption spectrum differs significantly from that of the monomeric counterpart in solution, suggesting the presence of strong interactions between the two tetracene subunits. In solution, the fluorescence spectrum is dominated by a band at around 535 nm, due to an oxidative impurity. In the longer wavelength range, a short-lived lower energy emission can be identified as the intrinsic emission of the dimer. In a polystyrene matrix or at low temperatures, the lifetime of the lower energy emission lengthens and it becomes more prominent. We suggest that the interactions between the two tetracene subunits produce a short-lived, lower energy "excimer-like" state. The fluorescence decays show no observable dependence on an applied magnetic field, and no obvious evidence of significant singlet fission is found in this dimer. This research suggests that even though there are strong electronic interactions between the tetracene subunits in the dimer, singlet fission cannot be achieved efficiently, probably because the formation of "excimer-like" states competes effectively with singlet fission.

Covalently linked perylenetetracarboxylic diimide (PDI) dimers (D1 and D2) and trimers (T1 and T2) with slipped “face-to-face” stacked structure are prepared and their molecular structures are characterized by 1H NMR, MALDI-TOF mass spectroscopy and elemental analysis. The rigid molecular structures of these compounds make it easier to establish a direct correlation between the aggregate structure and the photophysical properties. The minimized molecular structures of these compounds reveal that they are all “face-to-face” stacked aggregates with large longitudinal displacement. Their absorption spectra show red-shifted bands, suggesting the presence of “J” type excitonic coupling between the PDI subunits in these compounds. However, their steady state and time resolved fluorescence spectra revealed that the emission from the “excimer-like” states dominates the fluorescence of these compounds, this is similar to that of “H-type” aggregates and may be ascribed to the “face-to-face” stacked structure. In the fluorescence spectra of these compounds, a minor “J-type” emission can be identified for the compounds with a relatively large longitudinal displacement. An increase in the number of subunits in one aggregate from 2 to 3 also brings about distinctive changes in their photophysical properties, which can be ascribed to the changes in the stacking structure caused by the steric hindrance.

Colorimetric assays have drawn increasing research interest with respect to the quantitative detection of hydrogen peroxide (H 2 O 2 ) based on artificial enzymes because of their advantages with respect to natural enzymes, including design flexibility, low cost, and high stability. Regardless, the majority of the artificial enzymes exhibit low affinity to H 2 O 2 with large Michaelis−Menten constants (K m ). This indicates that the catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to blue-colored oxTMB requires a high H 2 O 2 concentration, hindering the sensitivity of the colorimetric assay. To address this problem, novel reduced Co 3 O 4 nanoparticles (R-Co 3 O 4 ) have been synthesized in this study via a step-by-step procedure using ZIF-67 as the precursor. R-Co 3 O 4 exhibits a considerably enhanced peroxidase-like activity when compared with that exhibited by pristine Co 3 O 4 (P-Co 3 O 4 ). The catalytic process in the case of R-Co 3 O 4 occurs in accordance with the typical Michaelis−Menten equation, and the affinity of R-Co 3 O 4 to H 2 O 2 is apparently higher than that of P-Co 3 O 4 . Furthermore, the density functional theory calculations revealed that the introduction of oxygen vacancies to R-Co 3 O 4 enhances its H 2 O 2 adsorption ability and facilitates the decomposition of H 2 O 2 to produce •OH radicals, resulting in improved peroxidase-like activity. A simple and convenient colorimetric assay has been established based on the excellent peroxidase-like activity of R-Co 3 O 4 for detecting H 2 O 2 in concentrations of 1−30 μM with a detection limit of 4.3 × 10 −7 mol/L (S/N = 3). Furthermore, the R-Co 3 O 4 -based colorimetric method was successfully applied to glucose detection in human serum samples, demonstrating its potential for application in complex biological systems.