Jun-Hua Wan

Self-assembly of novel fluorescent silole derivatives into different supramolecular aggregates: fibre, liquid crystal and monolayer

Two novel organogelators based on 2,3,4,5-tetraphenylsilole functionalized with long-chain alkoxydiacylamido platforms (1a and 1b) were synthesized. The silole derivatives induced gelation of only hydrocarbon solvents and showed aggregation-induced emission (AIE) in the gel state, in contrast to very weak emission in solution. The polarized optical microscopic (POM) and field emission scanning electron microscopy (FE-SEM) studies exhibited that the xerogels formed fibrous structures. Hydrogen bonding and π-stacking interactions were the main driving forces for the formation of organogels, based on the FT-IR and absorption investigations. Differential scanning calorimetry (DSC) and POM studies indicated that both compounds 1a and 1b exhibited stable liquid crystalline (LC) phases over a wide temperature range. It is interesting that uniform and well-ordered monolayers were also obtained for both compounds on the HOPG surface. The new silole derivatives are quite unique because they can self-assemble into one-dimensional (fibres), three-dimensional (liquid crystal) and even two-dimensional (molecular monolayer) aggregates.

Cruciform p-n diblock conjugated oligomers for electroluminescent applications

The optoelectronic properties of the cruciform p–n diblock oligomers 1–3 can be independently tuned by the oligofluorene and oxadiazole branches to increase the charge mobility.

Structural modification of thieno[3,4-c]pyrrole-4,6-dione: structure–property relationships and application in solution-processed small-molecule organic solar cells

We present a method for the modification of the structure of thieno[3,4-c]pyrrole-4,6-dione (TPD) to gain two novel acceptors TPN and TIN. And a series of donor–acceptor–donor-type oligomers 3TTPD3T, 3TTPN3T, and 3TTIN3T, based on TPD, TPN and TIN, have been designed and synthesized for solution-processed small-molecule bulk-heterojunction (BHJ) solar cells. The impact of these different central acceptor moieties on their optical, electrochemical properties, morphology, and solar cell performance were studied. Optical and electrochemical data showed that structural modification of TPD exhibited a slight impact on the band gap and HOMO/LUMO energy levels. Atomic force microscopy and grazing incidence wide-angle X-ray scattering studies revealed that the central acceptors of these oligomers played an important role in determine the morphology of solid-state packing. Oligomer 3TTPD3T showed weak crystallinity in a thin film. The larger conjugation plane counterpart 3TTPN3T showed an improved structure order. Surprisingly, the structurally twisted compound 3TTIN3T showed a strong crystalline nature with large crystalline domains of several hundred nanometers. The photovoltaic properties of these oligomers were evaluated by fabricating BHJ devices with PC71BM. 3TTPD3T/PC71BM blends with a weight ratio of 2:1 showed a best power conversion efficiency of 1.87%, with a Jsc of 4.93 mA cm−2, a Voc of 0.87 V, and a fill factor of 44%.

Novel ladder π-conjugated materials--sila-pentathienoacenes: synthesis, structure, and electronic properties.

A novel series of ladder π-conjugated materials--sila-pentathienoacenes (Si-PTA) are synthesized and characterized. Crystal structures of the compounds show that the length of alkyl chains substituting on the thiophene ring has a significant influence on molecular packing. A densely packed structure with an interfacial distance of about 3.66 Å between the adjacent molecules is observed for the compound with shorter alkyl chains. However, a large interfacial distance (7.99 Å) is obtained for another compound because of the insertion of long alkyl chains between two planes. The investigation of the optical and electrochemical properties shows that the silylene bridge incorporated into the pentathienoacene framework exerts a clear effect on the electronic properties by the σ*-π* conjugation. Although only a slight enhancement is observed for the HOMO levels, with respect to that of pentathienoacene, the LUMO levels are significantly lowered. The observed electronic properties are consistent with the theoretical calculations.

Donor–Acceptor Conjugated Macrocycles: Synthesis and Host–Guest Coassembly with Fullerene toward Photovoltaic Application

Electron-rich (donor) and electron-deficient (acceptor) units to construct donor-acceptor (D-A) conjugated macrocycles were investigated to elucidate their interactions with electron-deficient fullerene. Triphenylamine and 4,7-bisthienyl-2,1,3-benzothiadiazole were alternately linked through acetylene, as the donor and acceptor units, respectively, for pentagonal 3B2A and hexagonal 4B2A macrocycles. As detected by scanning tunneling microscopy, both D-A macrocycles were found to form an interesting concentration-controlled nanoporous monolayer on highly oriented pyrolytic graphite, which could effectively capture fullerene. Significantly, the fullerene filling was cavity-size-dependent with only one C70 or PC71BM molecule accommodated by 3B2A, while two were accommodated by 4B2A. Density functional theory calculations were also utilized to gain insight into the host-guest systems and indicted that the S···π contact is responsible for stabilizing these host-guest systems. Owing to the ellipsoidal shape of C70, C70 molecules are standing or lying in molecular cavities depending on the energy optimization. For the 3B2A/PC71BM blended film, PC71BM was intercalated into the cavity formed by the macrocycle 3B2A and provided excellent power conversion efficiency despite the broad band gap (2.1 eV) of 3B2A. This study of D-A macrocycles incorporating fullerene provides insights into the interaction mechanism and electronic structure in the host-guest complexes. More importantly, this is a representative example using D-A macrocycles as a donor to match with the spherical fullerene acceptor for photovoltaic applications, which offer a good approach to achieve molecular scale p-n junctions for substantially enhanced efficiencies of organic solar cells through replacing linear polymer donors by cyclic conjugated oligomers.