Impact of alkyl chain branching positions on molecular packing and electron transport of dimeric perylenediimide derivatives

Side chains play a critical role in tuning intermolecular interaction and charge transport in organic semiconductors. Here, we have systematically investigated the impact of branching positions of the alkyl side chains on the molecular packing and electron transport properties of a series of bay-linked dimeric perylenediimide(PDI) derivatives by atomistic molecular dynamics simulations in combination with charge transfer rate theory and kinetic Monte Carlo simulations. The results show that despite of different branching positions of the alkyl chains,π–π stacking is effectively inhibited for all the dimeric PDI derivatives. As the branching position moves away from the PDI backbone, the appearance of the alkyl atoms around the PDI backbone will first decrease and then increase. Correspondingly, the short contacts between the PDI moieties are first enhanced and then reduced. In particular, when the branching position is at the third carbon atom, the intermolecular connectivity becomes the most effective and the electron mobility is significantly increased by 2 times.

Tuning the optoelectronic properties of vinylene linked perylenediimide dimer by ring annulation at the inside or outside bay positions for fullerene-free organic solar cells

Among various perylenediimide(PDI)-based small molecular non-fullerene acceptors(NFAs),PDI dimer can effectively avoid the excessive aggregation of single PDI and improve the photovoltaic performance.However,the twist of perylene core in PDI dimer will destroy the effective conjugation.Thus,ring annulation of PDI dimer is a feasible method to balance the film quality and electron transport,but the systematic study has attracted few attentions.Herein,we choose a simple vinylene linked PDI dimer,V-PDI2,and then conduct further studies on the structure-property-performance relationship of four kinds of derived fused-PDI dimers,namely V-TDI2,V-FDI2,V-PDIS2 and V-PDISe2 respectively.The former two are incorporated thianaphthene and benzofuran at the inside bay positions,and the latter two are fused thiophene and selenophene at the outside bay positions,respectively.Theoretical calculations reveal the inside-and outside-fused structures largely affect the skeleton configuration,the former two tend to be planar structure and the latter two maintain the distorted backbone.The photovoltaic characterizations show that the inside-fused PDI dimers offer high open circuit voltage(VOC),while the outside-fused PDI dimers afford large short-circuit current density(JSC).This variation tendency results from the reasonably tunable energy levels,light absorption,molecular crystallinity and film morphology.As a result,PBDB-T:V-PDISe2 device exhibits the highest power conversion efficiency(PCE)of 6.51%,and PBDB-T:VFDI2 device realizes the highest VOC of 1.00 V.This contribution indicates that annulation of PDI dimers in outside or inside bay regions is a feasible method to modulate the properties of PDI-based non-fullerene acceptors.

Tuning Intermolecular Singlet Fission Efficiencies of Perylenediimide Derivatives through Bay Aromatic Substitution

Singlet fission(SF)has potential applications in high-efficiency photo-energy harvesting applications,but its practical application is hindered by the limited number of materials.In this work,we explored the bay aromatic substitution strategy for the design of new perylenediimide(PDI)based SF materials.A series of PDI derivatives with biphenyl or naphthalene units substituted at the bay posi-tions were designed and synthesized to investigate the effects of aromatic substitutes on their photodynamic behaviours.The bay substitutions do not shift the energy level of the PDI core significantly but give rise to different intermolecular coupling strengths in the thin films and affect the intermolecular SF efficiency.Femtosecond transient absorption(fsTA)spectroscopy reveals that appro-priate spacing configuration from the bay aromatic substitution groups enhances the SF yields by promoting the interaction of neighbouring PDI cores.Triplet exciton yields of up to 183%have been obtained from these new PDI derivatives,making them po-tential candidates in future SF-based optoelectronics.

All-Polymer Solar Cells with Perylenediimide Polymer Acceptors

Four polymers based on perylenediimide co-polymerized with thiophene, bithiophene, selenophone and thieno[3,2-b]thiophene were investigated as the acceptor materials in all-polymer solar cells. Two different donor polymers, poly[4,8-bis（5-（2-ethylhexyl）thiophen-2-yl）benzo[ 1,2-b;4,5-b＇]dithiophene-2,6-diyl-alt-（4-（2-ethylhexyl）-3-fluorothieno[3,4- b]thiophene）-2-carboxylate-2,6-diyl] （PTB7-Th） and poly[（5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl）-alt-（3,3＇-di（2- dodecyltetradecyl）-2,2＇;5＇,2＂;5＂,2＇-quaterthiophen-5,5＇＂-diyl）] （PffBT4T-2DT）, with suitably complementary absorption spectra and energy levels were applied and examined. Among all different donor-acceptor pairs studied here, the combination of PTB7-Th：poly[NN-bis（1-hexylheptyl）-3,4,9,10-pery,enediimide-1,6/1,7-diyl-alt-2,5-thiophene] （PDI-Th） exhibited the best power conversion efficiency （PCE） of 5.13%, with open-circuit voltage （Vo：） = 0.79 lV, short-circuit current density （Jsc） = 12.35 mA.cm-2 and fill-factor （FF） = 0.52. The polymer of PDI-Th acceptor used here had a regio-irregular backbone, conveniently prepared from a mixture of 1,6- and 1,7-dibromo-PDI. It is also noteworthy that neither additive nor post- treatment is required for obtaining such a cell performance.

Perylenediimide chromophore as an efficient photothermal agent for cancer therapy

Photothermal agents with improved bioavailabilities can generate heat from near-infrared light, which has been efficiently used for in vivo photothermal therapy （PTT） for cancer, with minimum tissue invasion. Strategies for developing organic near-infrared-absorbing molecules for phototfiermal cancer therapy have drawn intensive attention among academic investigators. However, conventional organic nearinfrared-absorbing molecules may not only have complex synthesis procedures, but also easily suffer from photobleaching under light irradiation. These drawbacks might lead to an increase in the synthesis cost, and elicit a risk of side effects in PTF. Thus, it is essential to devise an organic photothermal agent with stable phototbermal capacity, which involves a facile synthesis process. In this study, incorporating a secondary amine group （donor） in the bay regions of perylenediimides （PDls） could lead to a 150-nm bathochromic shift of the absorption maximum. Next, a modification of poly（ethylene glycol） （PEG） at the periphery of the chromophore renders the targeted macromolecule PDI-PEG highly water-soluble, and capable of intense absorption in the near-infrared region. The self-assembled PDl-based nanoparti- des （PDI-NPs） have a size of 55 nm in aqueous solutions. PDI-NPs with excellent photostability possess a high photothermal conversion efficiency of up to 43% ± 2%. Finally, PDI-NPs allow for efficient in vitro and in vivo photothermal cancer therapy. Meanwhile, PDI-NPs exhibit quite low cytotoxicity and no biotoxicity on major organs in vivo. Thus, these easily-manufactured PDI-NPs can serve as extremely stable photothermal agents for efficient photothermal cancer therapy.

Two novel rhodamine-perylenediimide fluorescent probes:Synthesis, photophysical properties, and cell imaging

In this study, two novel dual-switch fluorescent chemosensors based on rhodamine-peryleneiimide have been designed and synthesized. The dual-switching behaviors of the sensors were based on the structural transformations of rhodamine and an intramolecular photoinduced electron transfer（PET）process from rhodamine to perylenediimide. These probes exhibited excellent sensitivity to protons with enhanced fluorescence emission from 500 nm to 580 nm. The fluorescence changes of probes were reversible within a wide range of p H values from 2.0 to 11.0. Moreover, the sensors exhibited high selectivity, short response time, and long lifetime toward protons. The possible mechanism was investigated by the DFT calculation and-1H NMR. According to the experiment of confocal laser scanning microscopy, these probes could be used to detect the acidic p H variations in living cells.by the Fundamental Research Funds for the National Natural Science Foundation of China （No. 61178057） and for the Central Universities （No. CXLX12_0085）. The characteristic data of compounds were in the Supplementary information.