Synthesis And Properties Of Perylene Diimides Derivatives With Bay-Derived Cyclo-Tin-Conjugation And Polyploids

Organic solar cells?OSCs?have attracted much attention in recent years.The main projects to improve the OSC performance are designing new donor and acceptor electron materials.The fullerene-based acceptor materials have some disadvantages of the difficulty in modification,high cost and weak visible light absorption capacity.Due to the large conjugation,perylene diimides?PDI?derivatives exhibit such advantages of low price,easy modification,and strong visible light absorption,which are beneficial to the OSCs as the electron acceptors.However,PDIs have special property of strong?-?stacking between the intermolecular,which increases the exciton recombination rate.To weaken molecular stacking,the proposed strategy is twisting the spatial structure,and ensuring the electron transport properties.Based on the concept of introducing heteroatom to construct the new PDI derivatives,two metal tin ring-fused compounds?PDI-Sn and 2PDI-Sn?are designed and synthesized.The new compounds PDI-Sn and 2PDI-Sn have a larger conjugated structure,which give the reduced LUMO energy levels?-4.1 eV and-4.2 eV,respectively?,and red-shifted absorption spectra in the visible region.As a heavy atom,metal tin brings a triplet excited state effect,and its singlet oxygen yield increases from 13.0%and 7.8%to 48.5%and 40.4%,respectively.The lifetime values of the excited triplet state is also increased from the original nanosecond level to the microsecond level?about 18?s?,which are much longer than those of singlet excitons.All these results indicate that PDI-Sn and 2PDI-Sn are the promising acceptor materials for high efficiency OSCs.Then,we have designed and synthesized the polyploids 3PDI and 4PDI,which are directly connected to the bay-position and ortho-position of the PDI.The two polyploids have large extinction coefficients and increased visible light absorption range.The extinction coefficients of 3PDI and 4PDI are 98800 and 82800 M^-1cm^-1,respectively.And the visible light absorption edges of 3PDI is expanded to 600 nm and 4PDI for 640 nm.The LUMO energy levels of the two are-3.97 eV and-4.18 eV,respectively.The properties of enhanced visible light absorption capacity,matched potential energy levels,and enhanced electron withdrawing capabilities mean that these two molecules have the ability to act as electron acceptor materials for high efficiencies in OSCs.