Nonlinear Optical Properties Of Dyes With Terminal Amino Group Participating Resonant Structures

Organic optical materials have advantages of designable C-C skeletal structures,large nonlinear optical susceptibilities and fast response time, which have been widely used in the field of linear and nonlinear optics. As an important component of organic optical dyes, those dyes with terminal amino groups involved resonant structures may have important significance in the study of nonlinear optics. Terminal amino groups can connect with heterocycles containing oxygen, nitrogen and sulfur by conjugation structures. The nonlinear optical properties of these dyes change with the conjugated chain length, the type of substituents and terminal amino groups and the number of substituents and terminal amino groups. The research of nonlinear optical dyesare divided into two directions: solutions and films. Some dyes with terminal amino groups participating resonant structures(such as: phenoxaziniums, phenothiaziniums, cyanines, and so on) exhibit excellent third-order nonlinear optical properties in solutions and films. As a time-resolved spectroscopy technology, femtosecond transient absorption spectroscopy have the advantage of high precision and high sensitivity, which have been used to explain the reaction processes of ultrafast photochemical, photophysical and photobiological. By analyzing the transient absorption spectroscopy,the types of transient species, energy transition pathways, excited state lifetimes and other relevant parameters will be clearly exhibited. Therefore, the femtosecond transient absorption spectroscopy test will contribute to explain the photoreaction mechanism of dye solutions and films.Several dyes with terminal amino groups involved resonant structures are designed and synthesized in this paper. UV-visible absorption spectrum, SEM, TEM, AFM, Z-Scan and femtosecond transient absorption spectroscopy techniques are used to study the linear and nonlinear optical properties of films and solutions, the surface morphology of films and excited state lifetimes, this paper mainly divided into three parts:In the first part, a benzo[α]phenoxaziniumdye with a long alkyl chain is synthesized according to literature. Then, the films with different doping ratio(the proportion of dye: 10%, 33%, 40%, 50%, 100%) based on poly(4-vinylphenol) and dyeareobtained by spin-coating, and their optical properties are studied. The UV-vis absorption maximum of 100% dye film appears about 18 nm red shift than the monomer of benzo[α]phenoxazinium in acetic acid. Moreover, a shoulder peak is appeared at 660 nm of 100% dye film. These phenomena can be interpreted as the aggregation of dye in films. Transmission electron microscopy also proved this aggregation. Additionally, the third-order nonlinear optical properties of films are tested by Z-scan technique with a picosecond laser beam at 532 nm, and the third-order nonlinear optical properties transformed from reverse saturated absorptions to saturated absorptions with increasing ratios of dye indoped films.In the second part, one kind of N-tetraalkyl benzo[α]phenoxazinium dye is synthesized, the nonlinear optical property of this dye would not influenced on pH. Nonlinear reverse saturated absorption properties are obtained when Z-scan test are performed for different dye solutions(CH3CN, CH2Cl2 and H2O) at 532 nm.The films with different doping ratio(the proportion of dye: 10%, 50%, 100%) based on PMMA and dye are obtained by spin-coating. UV-vis absorption spectroscopy and TEM test can prove the dye aggregation phenomenon in doped films, but the aggregation is not as obvious as the first part. Doing the femtosecond transient absorption test for these optical films, various nonlinear optical properties are exhibited at different wavelengths, such as: reverse saturated absorption properties are exhibited in 480- 554 nm and saturated absorption properties are exhibited in 554- 780 nm of 10% doped films. Particularly, those films with different doping ratio all exhibit reverse saturated absorption properties at 532 nm, this phenomenon can be explained by the weak dye aggregation effect. Moreover, the kinetic process after excitation(S2â†'S1 and S1â†'S0) and lifetimes of these two excited states(k1 and k2) can be obtained by the data fitting.In the third part, four optical dyes were designed and synthesized. Main structures were composed of terminal amino groups and pyrylium salts, connecting by conjugated chains of different lengths. For the dyes with the same terminal amino groups, UV-vis absorption maximum of dyes with long conjugated chains appear red shift than those dyes with short conjugated chains. In order to obtain the nonlinear optical properties and kinetic process after excitation of these four dye solutions, femtosecond transient absorption tests were done. In particular, at 532 nm, those derivatives with shorter conjugation chains exhibit saturated absorption properties and the derivatives with longer conjugation chains exhibit reverse saturated absorption properties. Moreover, nonlinear optical properties of pyrylium derivatives in acetonitrile solutions are tested by Z-scan technique with a picosecond laser beam at 532 nm. The test results of picosecond Z-scan are consistent with femtosecond transient absorption spectrum at this wavelength.The study of nonlinear optical properties of benzo[α]phenoxazinium films in the first two chapters, filling the gaps in the field of benzo[α]phenoxazinium optical films. In the final chapter, we can control the nonlinear optical properties of dyes by changing the conjugation length. Due to the use of femtosecond transient absorption technique, the nonlinear optical properties of samples can be well explained in each wave band, and the type and lifetime of excited states can also can be obtained by fitting. Femtosecond transient absorption technology provides the possibility to explain the optical process in a very short period of time.