Construction Of Polycyclic Aromatic Hydrocarbons Containing Seven-membered Rings Based On Perylene

Curved polycyclic aromatic hydrocarbons（PAHs）,containing seven-membered rings,have drawn considerable attention due to their structural dynamic behavior,electronic properties,aromaticity and rich stacking modes.The insertion of seven-membered ring not only can cause negative curvature in the conjugated molecular framework,but also significantly change the electronic structure and physical properties through such specific defect-doping.At present,seven-membered aromatics show great potentials in applications such as organic light-emitting,organic semiconductor and stimulus-response systems.However,it is difficult to introduce seven-membered ring into polycyclic aromatic hydrocarbons,and the studies of these compounds are even in infancy.Therefore,in-depth understanding of these types of molecule is still undergoing and more functions and applications are expected.The paper has conducted design and synthesis of new conjugated molecules（BDBP and Per-TA-OH）with seven-membered carbon rings incorparted,which showed interesting topology asnegative saddle-shaped structures.The corresponding electronic structures and physical properties are investigated.The main contents as follows:1)By using dibromo-substituted perylene as starting material,compound BDBP containing a seven-membered carbon ring was efficiently constructed through successive Suzuki coupling,bromination and intramolecular palladium-catalyzed C-H arylation reaction.Compound BDBP showed reversible redox properties with two reversible oxidation processes and one reversible reduction process,which also exhibited fluorescence quantum yields in solution up to 86%.This may be due to rigid structure after the insertion of seven-membered ring in such conjugated peperylene moity,which cause non-radiative transitions deactivated.In addition,this type of compounds also show narrowed band gap.2)Chemical oxidation of BDBP,provided its radical cation and dication BDBP²⁺.The evolution of electronic structure,physical properties and aromaticity,compared to nutrual compound,were then studied.Results demonstrate that BDBP and BDBP²⁺have a trans saddle-shaped framework,with two enantiomers in the molecules.Interestingly,BDBP exhibited homochiral molecular arrangements,while BDBP²⁺were slip stacking of enantiomers.Besides,The seven-membered ring could maintains their conformation during oxidations.3)By using dibromo-substituted perylene as the starting molecule,another type of aromatics with sulfur-doped heteroazulene units（Per-TA-OH）was constructed through Pd-catalyzed C-H arylation reaction.The intrduction of thiazulene unit furthermore purtub the electronic structure and corresponding physical properties of conjugated seven-membered polycyclic hydrocarbon.Compared to its unfused precursor Per-Th-2a,compound Per-TA-OH showed a larger red shift with respect to the electronic absorption and emission.This is related to the molecular conjugation have extended conjugation and the reduction of HOMO-LUMO energy gap,resulting from the embedding of the thioazulene unit.To be noted,Per-TA-OH exhibiting dual-emission,which is desirable for functional materials of curved polycylic aromatics.