Design, Preparation, Properties And Applications Of Broadband Absorbing Optical Materials Based On Squaraine

With the rapid development of optical information technologies and the continuous exploitation of novel energies, especially with the application of various light sources and the development of solar energy, the quantity and quality of photoelectric functional materials in need are increasing day by day. The design, preparation, study and application of optical functional materials with novel structures and excellent performance have become one of hotspots for researchers to pursuit in the world today. Different conjugated organic optical absorbing materials that possess strong and stable optical properties have been reported and increased year by year. Among all the absorbing materials identified, i.e., phthalocyanine, metal complex, polymethine cyanine, polyacetylenes, squaraine, radical dyes and azo optical absorbing materials have been widely applied in the fields of printing and dyeing, photo-detector, biological probe, photodynamic therapy, optical data storage, laser printing, optical-emitting effect transistor, nonlinear optics, infrared photography and solar cells, and even in our daily life.To further explore the influence of the molecular structures, especially the influence of the non-covalent supramolecular self-assembly structures on the optical performance of materials, some azo-dyes and squaraine dyes with different terminal hydrogen-bonding recognition groups are designed and prepared. It is expected to construct different supramolecular nano-architectures based on strong hydrogen bond recognition effect, and to investigate the relationship between supramolecular structure and properties. On the basis of the researches, a novel squaraine dye with excellent optical absorbing performance is identified to detect cysteine real-timely under normal physiological conditions. To improve the thermal and optical stability and to deteriorate the intermolecular aggregation of optical materials, we will explore a generic and effective approach to incorporate nano-sized OV-POSS units into organic optical molecules through covalent bonding connection at molecular levels. At last, to explore the effect of anchoring abilities and conjugated degrees on the photoelectric conversion efficiency of dye-sensitized solar cells, some near-IR absorbing materials with the same chromophores but different substituent groups which possess different binding ability and conjugated degrees are designed and applied in dye-sensitized solar cells, and some conclusions are drawn. The main contents are as follows:1. The general principle of optical absorbing properties, the influencing factors on absorption intensity and absorption peak, and the development of optical absorbing materials home and abroad in recent years were systematically reviewed.2. Some azo-dyes and squaraine dyes with different terminal hydrogen-bonding recognition groups are designed and prepared. They construct different supramolecular nano-architectures based on different hydrogen bond recognition effect, respectively, i.e., random type, linear type and hyper-branching type or ribbon-like type and the self-assembled supermolecular nanostructure can be effectively controlled by tailoring the terminal hydrogen-bonding recognition groups of the amphiphilic molecules. Their absorption and emission spectra and thermal stabilities are significantly affected by supermolecular structures and changed regularly with the increase of the regularity. The relationship between supramolecular structure and properties are characterized and evaluated by FT-IR, SEM, TGA, UV-vis, Z-scan and fluorescent spectra and thermal calculation. For azo dyes, the UV-vis property, fluorescent property, thermal property, and non-linear optical property all change regularly with the structure regularity of the supermolecules formed. The reason may be that the architecture of the ordered supramolecular self-assemblies facilitates to enlarge the larger π-electron delocalization of molecules, to reduce energy gap between the highest occupied (HOMO) and the lowest unoccupied molecular orbits (LUMO) and so to facilitate intermolecular charge transfers. All these result in red-shift of linear absorbance spectra and better nonlinear optical (NLO) properties. While for squaraine dyes, the influence of the supramolecular self-assembly structures on their thermal stability and on the Stokes shift shows an abnormal decrease with the increasing regularity of the self-assembly. The reason may be that the aromatic Huckel "4n+2" rule of central C4O2ring is weakened or destroyed to a certain extent once the formation of hydrogen bonds.3.A new, real-time and sensitive colorimetric sensor, Di-N-methyl-N-hydroxyethyl aniline squaraine (SQ), has been identified and synthesized for the cysteine analysis based on the decrement of its UV absorbance (△4) in the neutral aqueous medium (pH-7.5). The proposed method was applied to analyse synthetic amino acid samples and human serum samples. The results show that the linear range of cysteine detection in aqueous medium at pH-7.5is10-700nmol·L-1with a correlation coefficient (R) of0.9984and a limit of detection (3σ, n=20) of3.9nmol·L-1. The relative standard deviation (R.S.D.) for cysteine detection was lower than4.1%(n=5). The proposed method possesses the advantages of simplicity, rapidity, high selectivity and sensitivity. This makes it possible for the first time the real time detection of cysteine under normal physiological conditions.4. Due to intermolecular charge-transfer and decreasing dipole-dipole and π-π stack interaction between the optical chromophores, optical absorbing materials are easy to form the aggregation to result in unstable property. Here a generic and effective approach for solving the aggregation effect of optical materials in the solid state was explored by designing two kind of squaraine-containing POSS-based hybrids. It is expected that incorporation of "huge" inorganic POSS nano particles into optical materials via covalent bonding connection can effectively decrease the strong dipole-dipole and π-π stack interactions, inhibit the intermolecular charge-transfer between adjacent squaraine molecules and improve the optical, thermal and chemical stability of resultant materials. Both theoretic calculation and experimental results indicate that the molecular design strategy is rational and efficacious. The resultant organic-inorganic hybrid optical materials effectively eliminate the aggregation of organic optical chromophoric groups via hindering intermolecular charge-transfer and decreasing dipole-dipole and π-π stack interaction between the optical chromophores, and exhibit good optical stability, i.e., the absorption peaks of hybrids display only a slight blue-shift even in the solid. Simultaneously, the hybrids also show significantly enhanced thermal and chemical stabilities in comparison with the precursory organic optical materials. The work provides a generic and effective strategy to prepare optical stable materials with high thermal and photo stability and also provides the opportunities for further incorporation of other functional groups, which may allow the building-in of the additional functions to the hybrids in the future.5. To investigate the influence of the structure, especially the anchoring groups and conjugated degrees of the dye on the photoelectric conversion efficiency of dye-sensitized solar cells, some near-infrared absorbing squaraine dyes with the same chromophores, but different substituent groups which possess different binding ability and conjugated degrees, are designed and prepared using di-6-bromo-quilidinyl squaraine and acrylic acid,1-butenoic acid and p-vinyl benzene sulfonic acid as raw materials. The resultant dyes are applied in dye-sensitized solar cells as sensitizers to explore the influence of anchoring abilities and conjugated degrees on the photoelectric conversion efficiency of dye-sensitized solar cells. The results show that the stronger the bonding ability of anchoring groups and the better the conjugation degree of the substituents, the higher the photoelectric conversion efficiency of dye-sensitized solar cells. The reason may be that the structure facilitates and accelerates electron transport and so decreases electron recombination at the interface.