Study Of Solid-state Fluorescent Properties Of Divinylanthracene Derivatives

In recent two decades, the study on organic photoelectric has grown rapidlywith numerousachievements in organic light-emitting diodes, organic field effecttransistors, organic photovoltaics, sensors and memories. The photophysicalproperties of molecules in solid state are closely related to their aggregatingstructures. Herein, my master’s thesis focuses on the relationship among thefluorescent properties, molecular structures and aggregating structures of organicmolecules, based on two divinylanthracene derivatives.1. The photophysics proproperties of a novel butterfly-like fluorescentmolecule BDPVA, which is designed based on the rational modification ofdistyrylanthracene are investigated. Due to the unique butterfly-like structure ofBDPVA, the molecule is not only slipped but also rotated with respect to itsneighboring one in the close stacking, and ends up with a rotation angle of67°alongthe b axis.Therefore, the excitonic coupling between neighboring molecules isdrastically reduced and the radiative decay rate is kept high.And the supramolecularinteractions help to inhibit the non-radiative decay processes, such as the rotationaland vibrational motions. Additionally the twisted structure of molecules alsoprevents the close overlap of π systems so as to eliminate the effects fromvibronic-vibrational coupling. As a consequence, a BDPVA crystal possesses quite ahigh fluorescent quantum efficiency of0.60.The high fluorescent quantum efficiency enables BDPVA’s potential in thepractical applications. The high-quality single crystalof BDPVA exhibits excellentamplified spontaneously emission properties. The threshold is about200μJ cm-2witha minimum peak width at half height of12nm and a high net gain of69cm-1, whichis comparable with polymer materials. Moreover, the BDPVA-based non-doped light emitting diode has a maximum brightness of24750cd m2, the current and powerefficiencies are also high as9.91cd A-1and7.78lm W-1, respectively. The resultsshow the bright future of BDPVA in the fields of organic solid-state lasers andelectroluminescence devices.2. Study about the effect of protonation on the solid-state fluorescentproperties of molecular clusters is carried out on a pyridine-containing derivativeBP3VA. It is the first time that the insight into the origin of the fluorescenceresponsive to protonation stimuli are provided through the study on the crystals. Inthe isolated state, the protonation of pyridine mainly affects the distribution of thefrontier molecular orbitals, which account for the low-lying vibronic transitions. Sothat, the absorption and fluorescence varied upon protonation. While in themolecular clusters, another factor should be the influenced aggregating structures.The distance between neighboring molecules is reduced owing to the strongintermolecular hydrogen bonds induced by the chloridion. The enhanced excitoniccoupling and electron delocalization lower the transition energy between the firstexcited state and the ground state, ending up with the fluorescence change in crystals.The fluorescence change of BP3VA powder originates from the transformationbetween microcrystals as illuminated by the fluorescence microscope images andwide-angle XRD. Our results may contribute to revealing the intrinsic nature offluorescence change upon acid/alkali stimuli in the solid state.