Synthesis Of Large π-Conjugated Triindole And Oligothiophene Derivatives And Their Two-Photon Properties

Organic two-photon absorption (2PA) material is one of the important branches of optical functional materials. In this thesis, we focus on the designing and synthesis of high fluorescent conjugated organic compounds with large 2PA cross section.We take triindole, oligothiophene as the electron donor cores, dimesitylboryl as the electron acceptor, and a series of qudrapolar and octapolar molecules were synthesized. The one and two-photon properties were measured, the main results are as following: 1. The synthesis and characterization of organic compounds.11 of new triindole derivated octupolar compounds with strong fluorescence were reported in this thesis. We also report 6 oligothiophene based quadropolar compounds, The structures and codes of these compounds are as following: Figure 2. Quadrapolar oligothiophene derivatives reported in this thesis.2. The crystal structures determined.New crystal structures of 11 compounds were reported, and 12 crystal structures were newly determined,8 of which are complicated octpoles and quadrupoles.The crystal structure data of the triindole derivatives show that:a. Triindole derivatives are C3 symmetric and has good planerity. The C-C single bonds connected the inner and out benzene rings in triindole are much shorter than normal C-C single bonds, indicating that the triindole core has good conjuctivity. b. The C-C single bonds connected the inner and out benzene rings in 2,7,12-trisubstituted triindole crystal structure is shorter than that in 3,8,13-trisubstituted triindole, indicating that the 2,7,12-trisubstituted triindole is better conjugated.In the crystal structures of oligothiophene derivatives, any two connected thiophene rings direct to opposite direction. In the structure of 4V, all the thiophene rings in are on the same plane. Figure 4. The crystal structure of 4V (up) and 5B (down).3. Linear photo physical properties.The absorption and emission maximum of 2,7,12-trisubstituted triindoles have red shifts from their 3,8,13-trisubstituted isomers. Along with there are more and more thiophene rings, the absorption and emission spectra of oligothiophenes have more and more red shifts, and when there are more than 4 thiophenes, the redshift become neglectable. All target compounds are highly fluorescent.4. Nonlinear photo physical properties.The 2PEF of most target compounds are reported, and also the 2PA cross section. The 2PA spectra we got were as figure 5. Most of the compounds have 2PA cross section larger than 1000 GM and some even 2000 GM. The active cross section of 2-BYT and 2-BET are as large as 1100 GM and 1000 GM. Figuer 5.2PA spectra of some compounds. (THF was used in the left spectra, and toluene in the right)The structure-two-photon property relationships of our compounds are as following:1. The 2PA cross sections of alkenes are larger than the alkynes. The active two-photon cross section is as large as 1100 GM, as it has the largest quantum yield. This is also the largest two-photon active cross section reported in this thesis.2. The calculations and measurements shows that, the two-photon properties of 2,7,12-trisubstituted triindoles are larger than their 3,8,13-trisubstituted analogues. The larger 2PA cross sections in 2,7,12-anologues are corresponding to the better conjugated structures in their crystal structures. The 2PA spectra of 2,7,12- trisubsituted triindoles is red shift from their 3,8,13-anologues.The energy of the peaks of 2PA bands of oligothiophenes are higher than that of the S1 bands, which is the characteristic of the 2PA spectra of quadrupoles. Along with the oligothiophene chain become longer and longer, the maximum of 2PA become stronger and stronger, and the spectra have red shift. However, when there are more than 4 thiophenes, the whole 2PA band become stronger, but the peak value stays the same.