As shown in Figure , the optimized molecule of K-1 exhibited a highly twisted conformation when viewed from the side, which favors the solid-state emission. The distance between the two tert-butyl groups is 25.41 Å. When viewed from the top, it was observed that K-1 has a non-planar cavity (Figure ). The distance between the top C-H bond and the bottom C-H bond was 9.18 Å, and the distance between the left and right phenyl group was 10.79 Å. Subsequently, DFT calculations were performed to collect the structural information on K-1 and K-2. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) distributions were depicted, the HOMO was mainly distributed on the triphenylamine (TPA) skeleton, while the LUMO were almost completely situated on the phenylcyano group (Figure ). Due to the strong steric hindrance from the o-methyl group, there was a large torsion angle between the phenyl ring and carbazole, resulting in the almost complete separation of the HOMO and LUMO. In comparison with macrocyclic K-1, the HOMO-LUMO gap of branched K-2 was even more narrowed (Figure ), leading to a red-shifted absorption maximum with respect to K-1, which was in consistent with the experimental results. Next, the one-step energy transfer process between the two AIEgens and PBTB were investigated. As shown in Figure , the absorption band of PBTB was well overlapped with the emission of K-1, therefore the fluorescence dye PBTB was selected as energy acceptor. Consequently, efficient energy transfer process from K-1 to PBTB was confirmed in the cosolvents of water/THF by using fluorescence spectroscopy. Upon excitation at 320 nm, the fluorescence spectra of K-1/PBTB assemblies showed a typical Förster resonance energy transfer (FRET) process with one isoemissive point: the fluorescence peak of energy donor K-1 at about 460 nm decreased, while that of energy acceptor PBTB around 600 nm enhanced with the increase of the PBTB concentrations (Figure ). Furthermore, fluorescence lifetime decay experiments at 460 nm were performed to further verify the energy transfer process for the K-1/PBTB assemblies (Figure and Table ). The decay curve of the K-1 was fitted as a double exponential decay with fluorescence lifetimes of 1 = 0.94 ns and 2 = 3.95 ns. By contrast, the lifetimes in K-1/PBTB assemblies were decreased to 1 = 0.70 ns and 2 = 2.80 ns under the same conditions, indicating efficient energy-transfer was indeed taken place between K-1 and PBTB. The above results suggested that the artificial LHS based on K-1/PBTB system was successfully constructed. To quantitatively evaluate the performance of this prepared LHS, the energytransfer efficiency and antenna effect (AE) were calculated, which were widely used as empirical parameters for the evaluation of light-harvesting ability. In this system, the ΦET was calculated as 82.6% (Equation S1), and the antenna effect was calculated to be 13.1 (Equation S2) at a donor/acceptor ratio of 1000:40 (Figure and Table ). In addition, the energy-transfer efficiency can be gradually increased with the K-1/PBTB ratio from 1000:5 to ). Moreover, the emission spectrum of K-2 effectively overlapped with the absorption spectra of the acceptor PBTB (Figure ), suggesting the possibility of energy transfer from K-2 to PBTB. As depicted in Figure , with addition of PBTB to K-2, the PL intensity of PBTB (acceptor) around 600 nm increased along with the decrease of K-2 (donor) emission at approximately 450 nm when excited at 335 nm in water-THF (19: 1; v/v). In addition, the fluorescence lifetime decay experiments of the light-harvesting system monitored at 450 nm were also performed (Figure ). The results showed double exponential decay with fluorescence lifetimes of 0.60 and 3.11 ns for K-2, which decreased to 0.45 and 2.30 ns after addition of PBTB, indicating the energy transfer from K-2 to PBTB (Table ). Therefore, the above data clearly demonstrated the efficient energy transfer from the K-2 to PBTB. The energy transfer efficiency was estimated to be 77.9% with a molar ratio of donor/acceptor of 1000:40 (Figure and Table ), and the antenna effect was calculated to be 37.2 at such donor/acceptor ratio, indicating the K-2/PBTB could also function as an efficient light harvesting antenna in aqueous environment. Given that the photosynthetic light-harvesting system in nature contains multi-step sequential energy transfer with multichromophoric assemblies, multi-step sequential energy transfer rather than simple one-step energy transfer is more meaningful for ALHS. Therefore, based on the efficient one-step energy transfer achieved by K-1/PBTB, we further investigated the two-step sequential energy transfer process. As depicted in Figure , the absorption region of the triphenylamine-based organic dye Z1 partially overlapped with the emission region of the K-1/PBTB complex, making it possible to realize the two-step FRET process. As shown in Figure , when excited at 320 nm, the emission intensity of K-1/PBTB at 600 nm showed a marked decrease with the gradual addition of Z1. Meanwhile, the maximum emission wavelength red-shifted from 600 to 700 nm, accompanied by a substantial increase in fluorescence intensity. The fluorescence decay experiments showed a decline of the fluorescence lifetime from the K-1/PBTB assemblies (1 = 3.63 ns, 2 = 11.22 ns) to the K-1/PBTB/Z1 assemblies (1 = 2.36 ns, 2 = 7.96 ns) when monitored at 600 nm (Figure and Table ). When the ratio of K-1/PBTB/Z1 reached 1000:40:14, the ΦET was calculated to be 66.4% and the AE was 18.2 (Figure ). Based on the prerequisites for efficient light-harvesting, we speculated that the relatively small overlap between the absorption spectra of Z1 and the emission spectra of PBTB could result in reduced energy transfer efficiency. In general, the above results indicate that K-1/PBTB/Z1 could realize an efficient two-step sequential energy transfer process. Encouraged by the above lightharvesting process of K-1/PBTB/Z1, K-2/PBTB complexes and Z1 were also suitable for construction of two-step energy transfer due to the partial overlap between the fluorescence emission band of the K-2/PBTB complex and the UV-visible absorption band of Z1 (Figure ). As presented in Figure , with the increment of Z1 concentration, the fluorescent intensity of energy donor K-2/PBTB complexes at 590 nm emission gradually decreased and the intensity of acceptor Z1 at 680 nm emission obviously increased. Simultaneously, the fluorescent color of K-2/PBTB/Z1 complex exhibited a significant change from orange to red (inset of Figure ). In addition, compared to the ΦET of K-1/PBTB/Z1, the result of the K-2/PBTB/Z1 at the same ratio was 60.4% (Figure ), exhibiting a small decline. In contrast, the AE values of K-2/PBTB/Z1 was 20.8. Moreover, fluorescence decay profiles were also performed in K-2/PBTB/Z1 system (Figure ). Compared with the lifetimes of K-2/PBTB, the result of K-2/PBTB/Z1 at 590 nm exhibited a significant decrease (Table ).