Theoretical Investigation On Intramolecular Electron Transfer Properties Of Photosensitizer Materials

Energy shortage and environmental pollution issues are becoming huge threats to human beings,and sustainable development of economy and society without destruction of natural resource and environment has attracted widely attention.Solar energy is regarded as one of the most crucial basic energy resources due to its abundant,pollution-free,easy-to-excavate properties.As the key photoelectronic material,photosensitizers can effectively achieve the solar-to-electric power conversion with the advantages of rapid response,low cost,high storage density,ease of modification,large-area fabrication,and thus exhibit a promising application prospect in solar cells,photosensors,and biomedicine fields.In this thesis,the intramolecular electron transfer?IET?properties of several kinds of photosensitizer materials were investigated by using the density functional theory?DFT?and time-dependent DFT?TD-DFT?approach,based on“Donor?D?–?-bridge–Acceptor?A?”design concept and relevant experimental findings.The research results of this thesis can not only explain the previous experimental results and elucidate the internal IET process and photoelectric conversion mechanisms,but also provide initial theoretical predictions and scientific evidences in the designing and screen of novel complexes as efficient photosensitizer materials.Based on the molecular geometry of the reference complex[?bpy?₂-Ru?pytp?Co?tren?]⁵⁺?where bpy=bipyridine,pytp=3-?pyridin-2-yl?-[1,2,4]triazino[5,6-f][1,10]phenanthroline,tren=tris?2-aminoethyl?amine?,a series of heterodinuclear Ru?II?-Co?III?complex by substituting the 2,2-dipyridyl ligands on donor subunit utilizing the phthalocyanine derivative ligands?Z?-N-?1H-isoindol-1-ylidene?-2H-isoindol-1-amine with tert-butyl groups in different positions were designed,and the photo-induced IET properties in acetonitrile?MeCN?solution were investigated.O ur results showed that all heterodinuclear Ru?II?-Co?III?complexes display Ru?Co metal-to-metal electron transfer?MMET?in the visible region.The photosensitivity involving spectral response range and absorption intensity,and IET rate,are improved by introducing?Z?-N-?1H-isoindol-1-ylidene?-2H-isoindol-1-amine as donor ligands.The Ru?Co IET rate in the newly designed complexes shows at least one order of magnitude larger than that in[?bpy?₂-Ru?pytp?Co?tren?]⁵⁺.Based on the molecular geometry of the most efficient sensitizer SM315 at present,a series of Zn centered porphyrin sensitizers by changing the?-bridge subunit in consideration of the effects from?-bridge length,heteroaromatic unit,longitudinal conjugation,and relative position of functionalized groups on the optical and electrical properties were designed,and the ground-and excited-state properties in tetrahydrofuran?THF?solution were investigated in detail.O ur results are shown as follows:For Zn centered porphyrin sensitizers,the increase in?-bridge length by adding phenyl group distances the electron distribution of LUMO away from anchoring group and sharply decreases the effective electron excitation at the long wavelength region.The introduction of heteroaromatics in?-bridge,especially electron-deficient units,stabilizes LUMO levels and improves the light-harvesting capability and donor-to-acceptor IET characteristic significantly.The extension of longitudinal?-conjugation in?-bridge broadens the B band and slightly strengthens and redshifts the Q band but results in undesired orbital overlap.Repositioning Phenyl/Thiophene group away from carboxylic acid enlarges the energy gap but yield more effective long-range IET processes with more electron,longer distance,lower orbital overlap,and moderate transfer rate.The results of this chapter highlighted the significant effect of the functionalized?-bridge on the IET properties of Zn centered porphyrin sensitizers.Based on the molecular geometry of the C u?I?-based sensitizer C3,a series of heteroleptic Cu?I?-based sensitizers were designed by modifying the donor subunit,in which three aspects including the steric-hinerance effect,?-conjugation effect,heteroatoms and heteroaromatic units effect were taken into consideration,and the IET properties in dichloromethane?DCM?solution were investigated.We evaluated the effects of functionalized donor and?-bridge subunits on the IET process of photoelectronic functional material moleculars by analyzing the molecular geometries,electronic structures,molecular orbitals,UV-Vis absorption spectrum,light-harvesting efficiency?LHE?,and IET parameters,such as the IET rate,transferred charge,electron transfer distance,etc.Our results showed that the heteroleptic Cu?I?-based complexes are inclined to form distorted pseudotrigonal pyramidal configurations with four-coordinated geometry index?₄ ranging from 0.905 to0.914.The absorption spectra of C u?I?-based complexes covers³00.0-600.0 nm region,and the lowest excitation states are crucial for efficient electron excitation and separation.Suitable energy levels of C u?I?-based complexes render them thermodynamically favorable for efficient electron injection into semiconductor and regeneration from electrolyte.Relative to?-conjugation,heteroaromatic groups introduced into ancillary ligands can significantly improve the property of C u?I?-based complexes by decreasing HOMO-LUMO gaps,red-shifting spectral range,strengthening absorption intensity,boosting light-harvesting efficiency,and promoting interfacial electron injection.Specifically,Cu?I?-based complex with dithiole-functionalized group exhibits outstanding optoelectronic property.