Aniline Schiff Base: Polymorphs And Properties

In the past decades,organic solid materials have been applied in organic light-emitting diodes,organic solid-state lasers and sensors because of their outstanding characteristics.At the same time,scientists devote themselves to improving performance of luminescent materials.The way of tuning the luminescent properties is changing the molecular structure at the early stage.In recent years,a new way of achieving tunable luminescence was discovered by changing arrangement of molecules,i.e.forming organic polymorphs.The polymorph-dependent emission properties not only propose a method of preparing tunable and controllable luminescent materials,but also put an insight into the relationship between molecular packing mode at the microscopic level and the optical properties.In this thesis,we synthesized two Schiff base compounds and formed polymorphs of them.The relationship of these polymorphs between crystal structure and luminescent properties was disclosed by a series of systematic studies.The applications of these materials were explored.1,In chapter ?,we synthesized an aniline Schiff base and prepared three kinds of polymorphs.They were distinguished by shape and luminescence.The blocked-shaped polymorph is non-emissive,while the needle-like and plate-like polymorphs display bright green and yellow emissions,respectively.These polymorphs possess obviously different molecular conformations and packing modes,which have influences on luminescent properties.The non-luminescent polymorph shows a unique response,i.e.?turn on? of green emission,to the vapors of aliphatic acids with two or three carbons in the main chain,while the luminescent polymorphs almost do not respond to these acids.We propose a new mechanism different from the common protonation mechanism that the acetic acid molecules enter blocked-shaped crystal and interact with molecules through weak hydrogen bonds,which makes some of the initially twisted molecules become more planar and,meanwhile,further restricts the molecular vibration.Both factors are beneficial to the luminescence.Many vapors were tested to investigate the responsive behavior,and then polymorph-dependent acid response is achieved for the first time.The properties indicate that the material benefits the further design of novel acid sensors and the development of safety protection of file information.2,In chapter ?,an N,N-dimethyl-p-phenylenediamine Schiff base compound with AIE property have been obtained.We prepared two polymorphs: yellow emissive crystal 1Y and orange emissive crystal 1O.1Y and 1O hold the similar packing modes but adopt different molecular conformation,displaying conformation-dependent emission color.Ultra-long rod-like orange crystals can be prepared and show excellent function of low-loss optical wave-guiding.Furthermore,both polymorphs exhibit typical amplified spontaneous emissions properties,which indicate the potential as laser media in organic solid-state lasers.In summary,we have synthesized two Schiff base compounds with polymorph-dependent luminescence.The crystal structures and optical properties were investigated carefully,which disclosed the relationship between luminescent properties and molecular conformation/packing mode in some way.The thesis not only offers a reference for intensively studying relationships of organic solid materials between structure and property,but also provides a new insight into design of new functional organic materials.