Study On The Structure-Character Relationship Of Fluorescent Organic Ammonium Salts

The generation of fluorescence is related to specific molecular structures and aggregated structures and the understanding of specific molecular structures and aggregate states is important for building fluorescent materials.A rigid structure such as an aromatic ring is a conventional fluorescent group.However,many small molecules having only a simple functional group,such as a tertiary amine,C=C,C?C,C=O,-OH,and an imide,also have fluorescence,and their fluorescence unit and fluorescence mechanism are different from traditional fluorescent molecules:?1?There is no obvious rigid large conjugated group,usually a non-conjugated double bond structure and a group which is easy to form a hydrogen bond;?2?The fluorescence in the dilute solution is weak,and the fluorescence is strong under high concentration or solid state conditions;?3?The research on the fluorescence mechanism has just started,and no consensus has been reached.And research on fluorescent substances containing unconventional fluorescent groups is now focused on polymers and amino acids.Our preliminary work indicates that the ammonium carboxylate salt and the nitrogen-containing heterocyclic imidazoline derivative which do not contain a large conjugated structure also have fluorescence,and the subject will further study the relationship between the structure and the fluorescent properties of these two substances.The fluorescence mechanism was elucidated from the single crystal structure and theoretical calculations,and its application was initially explored.This topic is of great significance for expanding the research range of fluorescent molecules and enriching the mechanism of fluorescence emission.The specific research content of this paper is as follows:1.A series of ammonium salts of monocarboxylic acid were synthesized by neutralization reaction.The effects of raw material structure and external factors on the fluorescence properties of the products were summarized and their luminescence mechanism was explored.Monoacids with different chain lengths?formic acid,acetic acid and propionic acid?were selected to react with ethylenediamine to compare their fluorescence properties;ethylamine,diethylamine and ethylenediamine were selected to react with acetic acid to compare the effects of organic amine on the fluorescence properties of their products;The single crystal of acetic acid-ethylene ammonium salt was cultured to explore the fluorescence mechanism in solid state,and the fluorescence emission mechanism in liquid state was clarified.The effects of temperature and pH value on the fluorescence properties of monocarboxylic acid-ammonium salt and its application in metal ion detection were studied.2.A series of ammonium salt polymers of polybasic carboxylic acids were synthesized,and the effects of structure and external factors on the fluorescence properties of ammonium salts of polybasic carboxylic acids are summarized and their fluorescence mechanism was explored.Ethylenediamine was selected to react with different polybasic carboxylic acids?glycolic acid,propylene tricarboxylic acid and ethylenediaminetetraacetic acid?to compare the fluorescence quantum yields of the three products;the reasons for the difference of fluorescence properties between acetic acid-ethylene ammonium salt and ethylenediamine-ammonium salt were studied,and the effects of temperature and pH value on the fluorescence properties of ethylenediamine-ammonium salt and its application in metal ion.3.A series of compounds containing imidazole rings were selected to explore their fluorescence properties and mechanism.A series of compounds containing an imidazole ring structure,imidazoline,2-methylimidazoline?2MZ?and 2-ethylimidazoline,all have blue fluorescence,and the substituent fatty chain length inhibits the emission of fluorescence.The presence of a unsaturated bond and ring structure in the imidazole ring increases the rigidity and planarity of the molecule,making it possible to generate fluorescence.In addition,the electron donor group?NH-?at the symmetrical position facilitates fluorescence enhancement,which is mainly due to the P-?conjugation,which increases the degree of?electron conjugation.4.The ammonium carboxylate salt system was constructed by reacting 2MZ with acetic acid,and the change of fluorescence properties before and after salt formation was compared to further clarify the effect of ammonium carboxylate structure on fluorescence.1)It was confirmed by ¹H-NMR,ESI-MS and FTIR that 2MZ and acetic acid were successfully combined to form 2MZA in the form of ammonium carboxylate,and the effect of structure on fluorescence properties before and after salt formation is discussed.2)The 2-methylimidazoline and the salt-forming solution can realize the rapid recognition of Fe³⁺with high sensitivity;The change in fluorescence intensity in the range of pH=2.0-5.0increases linearly,and can be developed as a pH sensor for quantitatively detecting an acid-base environment in a wide range of 2.0 to 5.0.In summary,the synthesis of a series of fluorescent small molecules of ammonium carboxylate is simple and the structure is clear.The study of their fluorescence mechanism will contribute to the development of the research of new non-traditional fluorescent compounds and their fluorescence mechanism.It has potential applications in sensors,bioimaging and so on.