Theoretical Studies For The Effects Of The Intermolecular Interactions On The Optoelectronic Properties Of Small Organic Molecules

As organic materials are more and more widely used in optoelectronic devices,it is important to investigate the optoelectronic properties of organic molecules.Compard with crystals with a long-range ordered structure,organic materials are usually constituted of single molecules which stack in a certain way.Thus,the interactions of molecules have great effect on the various properties of organic materials.In this dissertation,we mainly studied the three primary intermolecular interactions,i.e.,the hydrogen bond,the π-π stack and the dipolar interaction by using the theoretical calculation method.And the study can be divided into three parts:the effects of the intermolecular hydrogen bond on the fluorescence quenching process;the effects of the conjugation and the π-π stack on the charge transfer;the effects of the dipole layer on the optoelectronic device.In the first part,we chose the fluorenone-methanol(FN-MeOH)complex as a model,optimized the molecular geometry according to different electronic state and calculated the corresponding potential energy.By comparing the vertical excitation energies of the fluorenone-methanol complex and fluorenone molecule,we found that the intermolecular hydrogen bond would induce the shift of the vertical excitation state.We focused on the charge transfer process along the hydrogen bond in the excited states.We constructed the potential energy profiles and surfaces of the charge transfer states by using the relaxed scans.Based on the analyzing of the computational results,we demonstrated that the charge transfer would enhance the non-radiative transition.After that,we similarly studied the other two systems:the 4-(dimethylamino)benzonitrile-water/methanol(DMABN-H2O/MeOH)complex and the pyridine-water(Py-H2O)complex.In the second part,according to the Marcus electron transfer theory and the quantum mechanics model,we studied the two important parameters in the electron hopping rate:the reorganization energy and the transfer integral.We chose four small organic molecules with similar conjugated structure,and calculated the electron distribution and the reorganization energy of the single molecule.Based on the definition of the reorganization energy and the relationship between the conjugacy and the reorganization energy,we found that the greater the conjugacy,the stronger the ability of gain and loss of charge.Since the transfer integral is related to the frontier orbital energy and the energy level would be affected by the intermolecular interaction,we optimized the bimolecular structure of the vertical and the parallel arrangement,and calculated the transfer integral.According to the calculation results,we found that theπ-π stack would enhance the charge transfer.In the third part,we studied the mechanism of the dipole layer which is used to modify the electrode in the organic optoelectronic device by reference to a double-layer surface charge distribution(equivalent,opposite,uniform)model in the electrostatics.In view of the mechanism of the dipole layer,we chose nine kinds of small organic molecules with similar structure and different dipole moment.Eight of them have the carboxyl group which can react with the dangling bond on the surface of the metal-oxide electrode and form the orderly dipole layer structure.By calculating the dipole moment of the nine kinds of molecules,we compared the effects of the different functional groups on the permanent dipole moment.After that,we selected two kinds of them which have the similar magnitude dipole moment but in opposite direction to construct solar cells and OLEDs with simple device structure.By comparing of the performance of the device,we demonstrated that one can adjust the function of the dipole layer by changing the functional group of the molecule,and verified the calculation results.