Completely understanding the working mechanisms of sophisticated supramolecular self-assembly exhibiting competing paths is very important for chemists en route to acquiring the ability of constructing supramolecular systems with controlled structures and designed functions. Here, the self-aggregation behaviors of an N-heterocyclic aromatic dicarboximide molecule 1, boasting two competing paths that give rise to different supramolecular structures and exhibit distinct thermodynamic features, are carefully examined. First, a group of H-aggregates are observed when providing a medium driving force for aromatic stacking, and their formation is manifested as an anticooperative process. When exposed to enhanced strength of aromatic interactions, these H-aggregates are found to transform into J-aggregates via a cooperative assembly mechanism. With the assistance of a mathematic model accommodating two competing polymerization pathways, calculations are conducted to simulate and explain the thermodynamic equilibria of such a unique supramolecular system. The calculation results are highly consistent with the experimental observations, and some important properties are elucidated. Specifically, the anticooperative assembly mechanism generally promotes the formation of low to medium oligomers, whereas the cooperative path is more competent at producing high polymers. If the anticooperative and cooperative routes coexist and compete for the same molecule, the cooperative formations of high polymers are significantly suppressed unless a very high degree of polymerization can be achieved. Such a unique feature of concurring anticooperative and cooperative paths emerges to the H- and J-aggregates of molecule 1 and thus brings about the interesting sequential appearances of the two types of aggregates under conditions of continuously enlarged driving force for self-aggregation. Finally, based on the knowledge acquired from this study and by analyzing the steric features of 1 that influence its supramolecular packing motifs, a slightly modified molecular structure is designed, with which the intermediate H-aggregation state was successfully suppressed, and a single cooperative J-aggregation path is manifested.

An efficient functional mimic of the photosynthetic antenna-reaction center has been designed and synthesized. The model contains a near-infrared-absorbing aza-boron-dipyrromethene (ADP) that is connected to a monostyryl boron-dipyrromethene (BDP) by a click reaction and to a fullerene (C60 ) using the Prato reaction. The intramolecular photoinduced energy and electron-transfer processes of this triad as well as the corresponding dyads BDP-ADP and ADP-C60 have been studied with steady-state and time-resolved absorption and fluorescence spectroscopic methods in benzonitrile. Upon excitation, the BDP moiety of the triad is significantly quenched due to energy transfer to the ADP core, which subsequently transfers an electron to the fullerene unit. Cyclic and differential pulse voltammetric studies have revealed the redox states of the components, which allow estimation of the energies of the charge-separated states. Such calculations show that electron transfer from the singlet excited ADP ((1) ADP*) to C60 yielding ADP(.+) -C60 (.-) is energetically favorable. By using femtosecond laser flash photolysis, concrete evidence has been obtained for the occurrence of energy transfer from (1) BDP* to ADP in the dyad BDP-ADP and electron transfer from (1) ADP* to C60 in the dyad ADP-C60 . Sequential energy and electron transfer have also been clearly observed in the triad BDP-ADP-C60 . By monitoring the rise of ADP emission, it has been found that the rate of energy transfer is fast (≈10(11)  s(-1) ). The dynamics of electron transfer through (1) ADP* has also been studied by monitoring the formation of C60 radical anion at 1000 nm. A fast charge-separation process from (1) ADP* to C60 has been detected, which gives the relatively long-lived BDP-ADP(.+) C60 (.-) with a lifetime of 1.47 ns. As shown by nanosecond transient absorption measurements, the charge-separated state decays slowly to populate mainly the triplet state of ADP before returning to the ground state. These findings show that the dyads BDP-ADP and ADP-C60 , and the triad BDP-ADP-C60 are interesting artificial analogues that can mimic the antenna and reaction center of the natural photosynthetic systems.

Two novel meso-CF3 BODIPY-based fluorescent rotors have been rationally prepared and sensitively respond to viscosity in living cells with fluorescence “turn-on” effect, attributing to the special restricted rotation of meso-CF3...

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