Structure And Optical Properties Of Star-shaped Conjugated Molecule: The Density Functional Theory Study

Recent decades, the nature of the star-shaped molecular structure and chargetransfer through the introduction of the functional groups of the functional regulationto improve the transmission performance and luminous performance is improved, oneof the important means to explore new materials. However, it is not clearly for the starmaterial’s structure, spectroscopic properties and luminescence mechanism, relatedtheoretical studies on this field are still scarce. In this paper we studied and exploredthe molecule structure, Electronic Absorption Spectrum and charge transfer propertiesby using density functional theory(DFT) and time dependent density functionaltheory(TDDFT). It provides the theoretical basis for designing and synthesizing newstar-shaped material. The main works are as follows:(1) The geometries, electronic absorption spectra and charge transfer propertiesof five novel star-shaped compounds with different core (electron-rich core: nitrogen,triazatruxene and triindole; electron-deficient core:1,3,5-triazine, triquinoxaline),styrene as bridge and tetrathiafulvalene (TTF) as a terminal group, have been studiedby using density functional theory (DFT) method. The results show that LUMO levelsand energy gaps can be adjusted effectively via altering core. The time-dependentDFT calculation indicates that there are two absorption bands in300-450nm. Theresults of the transition density matrix and charge difference density reveal that highenergy excitation mainly arises from charge transfer from TTF donor moiety to coreand bridge moiety. The low-lying excitations in electron-deficient core compoundsare predominantly TTF donor-bridge and core charge transfer transition from twointra-branch. This differs from electron-rich compounds, whose low-energytransitions are assigned to prominently intra-branch localized excitation from TTFmoiety. The reorganization calculations show that the hole and electronicreorganization energy are nearly equal except NST, and CST shows the lowestreorganization energy.(2) The geometries, electronic absorption spectra and charge transfer propertiesof eight novel star-shaped compounds with different end group (triphenylamine,carbazole, bisthiophene, tetrathiafulvalene, phenothiazine, coumarin), differentconjugated bridge (styryl, Styryl thiophene, thiophene ethylene) and triazine as core,have been studied by using density functional theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) method. The results show that, the LUMOlevel of TrTE3TTF is the lowest, HOMO energy level is the highest and the bandgapis minimum, has a good hole and electron injection/transport properties. Theelectronic spectra of the eight compounds there are a main absorption bands in thevisible range, which is S0â†'S1Degenerate transition. Accept TrTE3TTF, the test ofseven compounds’ transition properties means that the two and three branch withinthe Ï€â†'Ï€*transition contribution. The stimulate transition density matrix indicatethat TTF end group star molecule there is a strong charge transfer transition, leadingto a low-energy excitation intensity decreases. The emission transition density matrixindicate that the cold exciton of compounds TrTE3TTF and TrTE3DBT mainlyconcentrate in one branch, while the remaining six compounds mainly in twobranches.