Design And Synthesis Of Novel Fluorescence Organic Molecules For Solid State Optical Applications

The main purpose of this research is to develop novel organic fluorescence dyes with high solid-state quantum yield or large two-photon absorption (TPA) cross section. We have designed and synthesized more than 60 new organic molecules, including oligo(phenylene vinylene) (OPV), indolic squaraine dyes. Both spectroscopic and theoretical methods have been employed to investigate the structure-property relationship. New strategies have been developed for design of TPA dye with high cross sections.The main results are as below:1. More than 60 new fluorescence dyes were designed and synthesized, including OPV, squaraine,5,11-dihydroindolo[3,2-b]carbazole (ICZ), boron-dipyrromethene (BODIPY) and tetraphenylporphyrin. These new molecules provide us a library of new materials for the structure-property relationship research.2. Through a combined experimental and theoretical investigation, we demonstrated that that halogenation can have positive impact to the solid state fluorescence and electrochemiluminescence (ECL) properties of OPV derivatives, which is in contrast to the conventional halogenation effects. The chlorinated OPV molecule exhibits a very high solid fluorescence quantum yield (91%), and the brominated molecule gives the highest ECL emission intensity. We have used different theoretical calculation methods (TDDFT, NTO and NBO) to provide insights to the physics behinds the observed positive halogenation effects.3. We have explored the preparations and applications of the organic micro-particles from four different OPV molecules. We firstly demonstrated micro-particles with different shape can be prepared, by analyzing their spectroscopic properties, we identified the material suitable for biological applications, which is OPV-C1. In the later section, we studied the OPV-C1 particle as in vivo fluorescent tracer, and studied their distribution, basic toxicity and metabolism in organism.4. Through a combined experimental and theoretical investigation, we demonstrated that the chlorine substitution at different positions affect the molecules spectroscopic properties through the different participation of Cl atom to the natural transition orbital and different e electron-vibration coupling effects. We have used theoretical calculation methods (TDDFT, NTO and NBO) to gain insights to the physics behinds the observed effects. Compared the solid fluorescent properties and the crystal packing structure, we confirm that the molecular conformation in crystal is crucial for high solid emission. The twist conformation can suppress the aggregation induced fluorescent quench and promote the solid fluorescence5 Through a combined experimental and theoretical investigation, we demonstrated that there are significant differences between Acetal OPV and aldehyde containing OPV in fluorescence quantum yeild, fluorescence lifetime, two-photon absorption (TPA) cross section and Raman spectra. This system can be potential used in the hydrogen ions detecting and imaging.6. We developed a new theoretical strategy for screening organic molecules with large TPA cross section. This method is based on morphology analysis of the natural transition orbitals (NTO) directly associated with the TPA transition. The in silico screening of indolic squaraine dye (ISD) derivatives has led to the discovery of a small molecule with TPA cross section as large as 8000 GM. We demonstrated that the designed molecule showed excellent properties in both in-vitro and in-vivo two photon excited fluorescence imaging applications.7. We have synthesized and characterized three new indole-squaraine dyes (ISDs). We perform systematic theoretical and experimental investigation on the chemical reactivity of the ISDs in both solution and on the surface of SBA-15. A new method for enhancing ISD’s chemical stability is discovered.