A Series of Hyperbranched Polytriazoles Containing Perfluoroaromatic Rings from AB₂‐Type Monomers: Convenient Syntheses by Click Chemistry under Copper(I) Catalysis and Enhanced Optical Nonlinearity

Abstract

In this paper, four new hyperbranched polytriazoles containing azo moieties, derived from different AB2‐type monomers, were successfully prepared through the “click” chemistry reaction under copper(I) catalysis by modifying the synthetic route. The polymers were soluble in organic solvents and exhibited good second‐order nonlinear optical (NLO) properties. Thanks to the self‐assembly of perfluoroaromatic moieties in the periphery, HP2 showed the best NLO properties, with the d33 value as high as 145.0 pm V−1.

Further improvement of the macroscopic NLO coefficient and optical transparency of hyperbranched polymers by enhancing the degree of branching

“…The whole synthetic route was very similar to our previous case of HPS1. 43 Fluoroborate S2 was used as an azo-coupling reagent to react with S1 to yield the AB 4 -type monomer M1, however, a much longer reacting time (about 40 hours) was required than that for the AB 2 -type monomer (about 12 hours), possibly due to the larger steric hindrance of S1. The polymerization procedure was also very similar to our previous case: rst, under copper(I) catalysis (the CuSO 4 /sodium ascorbate system), the hyperbranched polymeric intermediate, which possessed a large amount of unreacted azido groups in the periphery, was synthesized; and then, the end-capped group, another batch of catalysts and solvent were added to the reaction solution to react with the peripheric azido groups in the intermediate, to yield the nal polymers.…”

“…49 Considering that the d 33 value of an NLO polymer could be much different when measured by different methods or by different testing systems or even at different times, when we tested the SHG coefficients of HP1 and HP2, that of HPS1 was remeasured again, though it has been reported in our previous work. 43 Thus, the NLO coefficients of these three hyperbranched polymers (Table 2) were measured by the same testing system and at the same time.…”

“…25,43,46 The main reason was that the Ar/Ar F self-assembly effect could improve the site-isolation effect as discussed above, and decrease the strong dipole-dipole interactions among chromophore moieties during the poling process.…”

“…40 Fortunately, by modifying the synthetic procedure and using end-capping groups to avoid the self-oligomerization, 40 from 2009, we successfully prepared some soluble azo chromophore containing AB 2 -type hyperbranched polytriazoles (the synthetic route to a typical example, HPS1, is shown in Scheme 1), which demonstrated large NLO effects. [41][42][43] In this work, a similar hyperbranched polymer HP1 was also prepared (Scheme 2), but derived from an AB 4 -type monomer, which could enhance its DB value, according to some excellent previous studies by other scientists. 44,45 In some sense, the AB 4 -type monomer could be considered as the product of click chemistry reaction among three AB 2 -type monomers, therefore, aer click polymerization, the chemical structure of HPS1 and HP1 was the same, except their different degrees of branching.…”

“…As a result, the d 33 value of HP1 was enhanced to be 122 pm V À1 , higher than that of HPS1 (100 pm V À1 ). Based on our previous work, 25,43,46 we further used pentauorophenyl rings as isolation groups instead of the normal phenyl rings in the periphery of HP1 to prepare HP2. As expected, the d 33 value of HP2 was further enhanced to be 136 pm V À1 .…”