Theoretical Study On AIE Effect Of C-N Bond-anchored Multi-layer 3D Chiral Molecules

The discovery of novel multilayered 3D chiral molecules marks the birth for new chirality type.They have a sandwich-like three-layer structure and the side chains cannot be freely rotated due to the influence of central layer,they exhibit multicolour fluorescence and aggregation-induced luminescence（AIE）effect.Luminescence is enhanced in aggregation by molecules with AIE,overcoming the effects of concentration quenching in conventional organic luminescent materials.Multilayer 3D chiral molecules have unique structure and AIE,allow they have potential applications in luminescent materials.Since the AIE mechanism has not been clarified,starting from the crystal structure of C-N bond-anchored multilayer 3D chiral molecules,the relevant parameters such as geometric structure of they in different aggregate states are theoretically discussed and obtain the mechanism of the AIE effect for C-N bond-anchored multilayer 3D chiral molecules.The details of this thesis are as follows:1.The theoretical research methods for AIE effect of C-N anchored multilayer 3D chiral molecules are discussed.Using a quantum chemical approach,2-X-1,3-bis（8-（4-Y-phenyl）na-ph-thaalen-1-yl）-1,3-dihydrobenzo[d][1,3,2]diazapho-sphole-2-oxide（A.X=NH₂,Y=H;B.X=i-Pr,Y=H;C.X=NH₂,Y=OMe）as study object,the predicted values of the maximum absorption and emission wavelengths using several functionals for molecules in solution were compared with experimental data and determined using B3LYP-D3（BJ）/LR-PCM/6-31G（d）for the calculations.Comparing the structures of A,B and C by GAFF and density functional theory in vacuum,expliciting that GAFF can be used in molecular dynamics（MD）simulations and QM/MM calculations.Testing the accuracy of the calculations for different QM/MM methods,the result shows that using B3LYP and GAFF lead the simulation more accurate.The scheme was validated by extracting molecular clusters of A from crystals and showing its suitability for theoretical simulations of crystal structures.Base on above tests,the combined quantum mechanical,MD and QM/MM methods applicable to the calculation of AIE effects for A,B and C was obtained.2.The theoretical study of AIE effect for C-N bond-anchored multilayer 3D chiral molecules was analyzed.The geometric and electronic structures of A,B,and C in solution,crystals,and aggregation were analyzed by combinatorial approach.The geometric changes are mainly concentrated on naphthalene and benzene rings,when molecule is excited from S₀to S₁ state.The geometric structure change is small in aggregation and crystal than solution,indicating that aggregation limits the change.The excitation characteristics of S₁ in different states are charge-transfer excitations.The rotational energy barriers of three molecules in gas were investigated.The three-layer structure was stable,but it could not limit the small twist of benzene and naphthalene rings and thus could not prevent the energy consumption generated by them.The non-radiative processes of the three molecules in different states are discussed by Huang-Rhys（HR）factor,and reorganization energy(E_reo).The HR factor and E_reo of the low-frequency vibrational modes are smaller when the molecules in aggregation than solution and these modes have an important role in nonradiative transitions,which are attributed to the twist vibrations of benzene and naphthalene rings.Taken together,the results indicate that aggregation restricts the rotation of the benzene and naphthalene rings of molecules A,B and C while limiting the low-frequency vibrations,resulting in a reduction in the nonradiative transition rate of the molecules then shine in aggregation.3.Clarify the excited state transition characteristics of（1-（7-（8-phenylnaphthalen-1-yl）benzo[c][1,2,5]thi-adiazol-4-yl）naphthalen-2-yl）phosphine oxide.The vertical emission energy of D was calculated with various functionals.The optimal control functional:ωB97XD*（ω=0.132）has the best performance.The UV-visible spectra of D and its same skeleton molecules were simulated using theωB97XD*and compared with the experimental spectra,the results show that this functional is applicable for this class of molecules.The hole-electron parameters and their overlays of D were plotted using hole-electron analysis.The interfragment charge transfer in S₁ state of D was quantitatively analyzed by intramolecular interfragment charge transfer methods.It is determined that the S₁ state excitation characteristics of D exhibit hybridization localization and charge-transfer excitation,the charge-transfer percentage is 44.7%,which is different from the charge transfer excitation of C-N bond-anchored molecules,suggesting that the molecular skeleton has an important influence on excited state charge transitions..From the above study,this thesis determines the theoretical mechanism of C-N anchored multilayer 3D chiral molecule and the AIE was the aggregation differentially restricts the twisting motion of benzene and naphthalene rings together with the low frequency vibration.These work explored the luminescence effect of AIE of C-N bond-anchored multilayer 3D chiral molecules,which will help advance its wide application in luminescent materials.