Synthesis And Near Infrared Absorption Performance Of Squaraine Dyes

Squaryliums have a good absorption in near infrared region (NIR) especially beyond the wavelength of 800nm as near infrared absorbing dyes. At this region, they have high absorption intensity and narrow absorb bandwidth. All those performance are just fitted to laser protection and stealth. Focused on the dire need of laser stealth materials, we propose the squaraine dyes as NIR absorption material to be used in the laser stealth technology, and the research was done on the preparation and near infrared absorption properties of six kinds of squaryliums.Based on the structure design of dyes,we adjused molecular structure to design a series of compounds. Finally we choosed six of them as subject investigated and simulated the IR spectrum and NMR spectrum, computed the basic thermodynamics by Hyper Chem and ascertained synthetic route. Using m-aminophenol as the precursor, we got the target product by a series of synthesis process including nitratlon reaction, nitroreduction, chain reaction on benzene, nucleophilic substitution at Nitrogen, synthesis of benzoxazintone and condensation between squric acid and benzoxazintone.The ratio of solution, reaction temperature, reaction time, type and amount of catalyst and recrystallization solution were studied in this paper to find the influence on the productivity and crystal morphologies of squaryliums. IR, NMR and SEM results show that the obtained compounds are the required product.The result shows that the optimal reaction temperature was 108℃and reaction time was 37~53h. By contrast, symmetrical squaryliums needed less time for preparation than unsymmetrical squaryliums. Compared with quinoline, using pyridine as catalyst, less time was needed but the reaction rate was much lower. Procuctivity was between 36~46% under the optimal reaction condition. Recrystallizated by acetone can get purest product. Crystal presented different morphologies such as feathery, neddle and strip shapes.On basis of traditional reaction, microwave synthesis, a new way of preparation, was used in squarylium preparation to save time and improve efficiency. The results shows that the best microwave power was 900W and the right microwave time was 20 min. At this condition, productivity was 23.7%.NIR absorption performance shows that N,N-diaminomethyl and N,N-diamino- ethyl increased the chain length and then increase polyenoidsystem, inductivity. Adding methyl onto the bridge chain amplified molecular absorption anisotropy and steric atabilizer then reduced absorption intensity. The results show that NIR absorption come from electronic transition in chain partition structure. Intensity of unsymmetrical squaryliums are much smaller than symmetrical squarylium about 20%~35%. Unsymmetrical squaryliums has absorption band at 380~780nm.The influence of external environment on NIR performance was studied using NIRSQ-01 and NIRSQ-05 as the subject. The result shows that polar solvent can reduce absorption intensity of symmetrical squaryliums, and a blue shit of the optical absorption was observed. The best testing condition was 0.01g/ml, less than 50℃.There are two kinds of squaryliums satisfacted using in laser stealth were synthesised. Theirλmax near 1.06μm and has sharp absorption. Adding N,N-diaminoethyl as terminal group or N,N-diaminomethyl as terminal group leading methyl into bridge chain just NIRSQ-01 and NIRSQ-05 have sharp absorption near 1.06μm and can be used in laser stealth material.