This work reports the synthesis and characterization of two blue emitters. Their 3D rigid structures are the appealing feature.

Spiro-OMeTAD is the well-known hole transporting material (HTM) in perovskite solar cells. In this work, its derivatives, namely four D-A shaped triphenylamine or biphenylamine endcapped indenone spirofluorene (SFD-TPA, SFD-OMeTPA, SFD-TAD, and SFD-OMeTAD), were designed and synthesized. With the introduction of electron-donating moieties and the extension of conjugation length, a series of changes in photophysical and electrochemical properties could be detected. Notably, in comparison with the optical gap (2.96 eV) of the reported spiro-OMeTAD, SFD-OMeTAD presents an optical gap as low as 1.87 eV. Moreover, density functional theory simulations were employed to further investigate their geometric and electronic structures. Finally, steady-state photoluminescence measurements proved the efficient charge separation and collection processes at the perovskite/HTM interface. It can be predicted that all four compounds with enhanced sunlight absorption capability and suitable frontier energy levels can be used as hole-transporting materials for perovskite solar cells.

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Light-induced structural transformation of 4-(amyloxy)cinnamic acid (AOCA) on the surface of highly oriented pyrolytic graphite (HOPG) was investigated with scanning tunneling microscopy (STM). AOCA molecules form highly-ordered adlayer on HOPG spontaneously, stabilized by hydrogen bonding between neighboring molecules. After UV-light irradiation onto the adlayer, the ordered adlayer was disrupted and a new disordered structure was observed, which indicated that dimerization of AOCA molecules took place. The STM results reveal the direct evidence for the photoisomerization of cinnamic acid at atom level. Keywords: scanning tunneling microscopy (STM), 4-(amyloxy) cinnamic acid (AOCA), self-assembly, light-induced reaction.With the development of the nanoscience and nanotechnology, scientists try to use single molecule to fabricate electronic device, and the so-called "bottom-up" technology was considered to be one of the effective methods, which constructs molecular electric circuit [1] . Self-assembling method plays an important role in the "bottom-up" technology. The scientists attempted to construct and assemble components from atoms and molecules. The structure of the self-assembled monolayer mainly depends on the chemical structure of molecules used in the SAMs. However, simple external stimulus such as heating, light irradiation and electric and/or magnetic fields can also tune the structures of SAMs. Owing to the potential application in molecular electronics, the studies about molecular assembly have attracted much attention [1] .Scanning tunneling microscopy (STM) provides a powerful tool for addressing two-dimensional molecular assemblies on a solid surface with atomic or submolecular resolution [2][3][4] . The light-induced changes in photochemical reactive adlayers at HOPG surface were investigated previously [5][6][7][8][9] . For example, Schryer et al. [10] studied the cis-trans isomerization of azobenzene derivatives. Qiao et al. [5] studied the polymerization diacetylene compounds in physisorbed monolayers. Cinnamic acid is a typical photoreactive compound. The study of photoinduced structural transformation in a monolayer is crucial to understand the surface chemical reaction and to develop photoresponsive and electronic nanodevices as well as novel nanomaterials [9] . There exist three forms of the compound in its solid crystals, α, β and γ. As shown in Fig. 1, the α-form monomers give the dimeric product of α-truxillic acid, whereas the β-form monomers produce β-truxinic acid, and the γ-form of the monomers is photostable. In a previous paper, we observed the photoinduced structural transformation of 4-(amyloxy)cinnamic acid (AOCA) on an Au(111) surface. A dimerization of the AOCA molecules and structural transition in the adlayer were clearly observed in STM images [8] . It is well known that the adsorption structure has some relationship with the substrate. Therefore, we attempt to study the surface two-dimensional adsorption structure and photoreaction of cinnamic acid derivative on the graph...