Li Yuren,Yan Lihe,Si Jinhai,Liang Zezhou,Huang Wenbo,Ma Heping,Hou Xun
The nonlinear optical limiting (OL) property of tin phthalocyanine porous organic frameworks (Sn-Pc-POFs) dispersion in the nanosecond regime was studied, which showed excellent dispersibility and stability as well as a low OL threshold. To clarify the nonlinear optical response mechanisms in the material, the energy level structure of Sn-Pc-POFs was simulated using the density functional theory calculation, and the photoinduced carrier dynamics was studied using femtosecond time-resolved transient absorption spectroscopy. The results indicated that the large absorption cross section and long lifetime of the excited state were responsible for the excellent OL property of the material.
Topological Photonics, exploring the topologically nontrivial states in photonics, is a fast-progressing research topic. Topological flat bands, fascinating features in topological photonics, have attracted much attention recently. Metal-phthalocyanine (MPc) molecular semiconductors are formed by molecular chains, offering a great platform to study topological states in low dimension. Previous work shows that the MPc molecular chain could be used to realize one-dimensional topological excitons based on the two-level systems. Therein, the topological flat band is a key feature in this type of topological excitons. Here, we have synthesized tin-phthalocyanine (SnPc) nanosheets. The ultraviolet–visible (UV–vis) and photoelectric experiments on these SnPc nanosheets are performed to characterize the one-dimensional topological flat bands. We demonstrate the strong evidence that the two photocurrent peaks at the wavelengths of 455 and 850 nm could originate from the topological flat bands within the B- and Q-spectral regions, respectively, according to our excitonic model. In addition, the photocurrent is improved by up to two orders using the nanosheets compared to the raw materials. Moreover, the previous excitonic model consisting of two-level systems is further generalized to incorporate both the B- and Q-bands by using three-level systems, interpreting the UV–vis spectra and the photocurrent peaks properly. The combination of our experimental and theoretical research shows that the stable and high broadband photoelectric performance of the SnPc nanosheets not only provides a new material platform for the organic photodetectors but also opens up a new research avenue for the observation of the topological flat band using molecular materials.
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