No abstract

Controlled regulation of the switchable behavior of the supramolecular network is central to the potential application in the molecular scale nanodevices. In this work, it is reported that the reversible accommodation of the guest molecules in the nanoporous supramolecular network can be regulated by the UV/visible light. The nanoporous complex template of TCDB/4NN-Macrocycle(trans,trans,trans,trans) with photosensitive units is well-defined. After the UV irradiation, the template can be switched on to encapsulate coronene molecules due to the formation of a new photoisomer(trans,cis,trans,cis) and switched off to expel coronene from the inner cavities under the visible light. The photoregulated switchable multicomponent supramolecular guest-host network provides a novel strategy for fabricating the functional nanodevices at the molecular scale.

Fullerenes have attracted a great deal of attention since their discovery [1] because of their unique physical and chemical properties and potential applications.[2] Many applications require the deposition of fullerenes onto a variety of surfaces including metals [3][4][5][6] or semiconductors. [7] The fabrication of ordered arrays of fullerenes on solid surfaces is of interest from both scientific and technological viewpoints. It has been demonstrated that fullerenes can form well-ordered arrays on metal or semiconductor surfaces under ultrahigh vacuum (UHV) conditions at low temperatures. [8][9][10][11][12] The arrangement is determined by the size and symmetry of the fullerenes and rigidly maintains its shape. On the other hand, C 60 is highly mobile at room temperature (RT) even when adsorbed on metal surfaces, and has no preferential orientation unless cooled to low temperatures. [13][14][15][16][17][18][19][20] Therefore, a well-decorated surface, which serves as a molecular template and provides binding sites, is important and necessary for the fabrication of highly ordered arrays of fullerenes at RT. Open porous networks obtained by metal-organic coordination, [21] the formation of hydrogen bonds, [8] or even van der Waals interactions [22][23][24] have been successfully used to direct the formation of ordered fullerene arrays. In this way the interfullerene distance and symmetry of the arrangement are solely determined by the molecular template and can be changed by adjusting its structure. More importantly, interactions between fullerenes can also be modified with this strategy.We have designed and synthesized a tetraacidic azobenzene molecule NN4A (Figure 1a) that exclusively forms KagomØ open networks with two types of cavities that have different size and symmetry at the liquid-solid interface. These cavities are capable of accommodating fullerene molecules as guest species. Herein, we examine the site selectivity of the networks for different fullerenes, a feature which has not been observed for other systems at liquid-solid interfaces. Azobenzene derivatives are typical photochromic compounds that have a wide range of potential applications, including for optical switching, holographic storage, light harvesting, long-term energy storage, and nonlinear optical materials. [25,26] The attractive photosensitive properties of azobenzene compounds have resulted in them being utilized as photoswitching units to control the structure and function of supramolecular systems. [27][28][29][30][31] Thus, the use of azobenzene units in the host matrix could allow for further control of the host-guest architectures.When deposited onto a graphite surface, NN4A forms a well-ordered open network with a KagomØ structure which is correlated to molecular geometry and network symmetry. [32,33]

The macrocyclic compounds consisting of photosensitive units as parts of the frame have been extensively studied to mimic photoregulated functions in nature. In this paper, controlled assembly of well-ordered arrays of photosensitive macrocyclic rectangles is demonstrated by using a host-guest molecular template. 4NN-Macrocycle molecules are observed to photoisomerize from trans-trans-trans-trans (t,t,t,t) to a range of isomers including trans-trans-trans-cis (t,t,t,c) and trans-cis-trans-cis (t,c,t,c) isomers after irradiation of UV light. The photoisomers are also observed to affect the guest-host network characteristic appreciably. In the STM observations we can distinguish three (t,t,t,t) conformational isomers, three (t,t,t,c) conformational isomers, and one (t,c,t,c) isomer, which self-assemble into different adlayers with TCDB on a HOPG surface. This study provides a facile approach to study the photoisomerization processes of the azobenzene groups and the conformational photoisomers.

Transparent, conductive, and flexible multiwalled carbon nanotube (MWCNT)/graphene hybrids with two three-dimensional microstructuresan interconnected network and a double-layer structurewere prepared. The conductivity and performance of MWCNT/graphene films can be controlled by different microstructures. A photoswitch using a layered heterostructure of a CdTe quantum dot on an interconnected MWCNT/graphene (IN-MWCNT/graphene) electrode shows an enhanced reversible photocurrent with a higher on/off ratio than that of double-layer structures (DL-MWCNT/graphene). Electrochemical capacitors using a IN-MWCNT/graphene network also exhibit an outstanding rate capability and good cycling stability due to a large surface area and high porosity. Results indicate that the IN-MWCNT/ graphene hybrid with porous structures and strong π-interaction is an excellent conductive network for multifunctional flexible devices. The performance of MWCNT/graphene hybrid films can be further optimized by the improved interface and microstructures.

An enhanced photoinduced reversible switching of graphene oxide-azobenzene (GO-AZO) hybrid was investigated as a highly sensitive photoswitch. The internal short-range ordered crystalline structure of GO-AZO hybrid was advantageous to charge transfer. The AZO moieties on GO underwent a rapid trans-cis photoisomerization upon ultraviolet irradiation due to the electron interaction between AZO and GO. The GO-AZO hybrid film showed an enhanced reversible photoswitching performance with high on/off ratio of 8 and fast response time less than 500 ms. The high sensitivity of GO-AZO switch arises from the intramolecular donor-acceptor architecture with efficient charge transfer.

Graphene quantum dot (GQD) is an emerging class of zero-dimensional nanocarbon material with many novel applications. It is of scientific importance to prepare GQDs with more perfect structures, that is, GQDs containing negligible oxygenous defects, for both optimizing their optical properties and helping in their photovoltaic applications. Herein, a new strategy for the facile preparation of "pristine" GQDs is reported. The method we presented is a combination of a bottom-up synthetic and a solvent-induced interface separation process, during which the target products with highly crystalline structure were selected by the organic solvent. The obtained organic soluble GQDs (O-GQDs) showed a significant difference in structure and composition compared with ordinary aqueous soluble GQDs, thus leading to a series of novel properties. Furthermore, O-GQDs were applied as electron-acceptors in a poly(3-hexylthiophene) (P3HT)-based organic photovoltaic device. The performance highlights that O-GQD has potential to be a novel electron-acceptor material due to the sp(2) hybridized carbon atom dominant structure and good solubility in organic solvents.

In this paper, an azobenzene derivative containing two diacetylene groups is synthesized and its self-assembly at a surface investigated using scanning tunneling microscopy (STM). Both the azo-benzene and diacetylene groups are photoactive, and the results show that surface assemblies of the targeted compound undergo polymerization following irradiation at 254 nm and reversible isomerization following alternating irradiation at 365 nm and with visible light. This is the first report of a STM investigation observing both photopolymerization and photoisomerization simultaneously for the same molecular assembly at an interface. The target molecule allows one to induce sequential and reversible structural changes to surface assemblies via multiple optical treatments, and is thus of both fundamental interest for surface science and engineering. These results provide experimental and theoretical guidance for the fabrication of future molecular optoelectronic devices.