Fluorescence And Third-order Non-linear Optical (NLO) Properties Of Polymers Containing Benzothiazole Moieties

Polymer materials with fluorescent and third-order nonlinear optical (NLO) properties have received much attention for they remain good optical properties of small molecules and excellent processabilities of polymers. Many benzothiazole derivates can be covalently bounded to polymer chain as a result of their photophysical and thermal stability. Novel benzothiazole-containing initiators and monomers with fluorescent or NLO properties can be synthesized using chemical modification method. By selecting functional ATRP initiators and monomers, functional polymers can be obtained.In this thesis, we focused on the design, synthesis and characterization of novel polymers containing benzothiazole moieties for fluorescent materials and third-order NLO materials. The fluorescent and third-order NLO properties were studied. The work can be summarized as follows:(1) A novel initiator, 2-benzothiazol-2-yl-5-bromomethyl-phenol (BYBP) containing excited state intramolecular proton transfer (ESIPT) fluorophore was synthesized. Atom transfer radical polymerization (ATRP) of styrene was conducted successfully using BYBP as an initiator. Factors such as the reaction temperature and mole ratio of catalyst to initiator, which could affect the ATRP system, were discussed in the paper. Chain extension was conducted using polymer as the macro-initiator which was characterized via H NMR. The optical property of initiator was well preserved in the obtained polystyrene, and the end-functionalized polystyrene exhibited obvious fluorescent emission at about 530 nm. The Stokes shift was about 190 nm.(2) A new initiator, 2-bromo-2-methyl-propionic acid 4- (2-benzot hiazole-2-yl-vinyl)- phenyl ester (BPBVE) was synthesized for the heterogeneous atom transfer radical polymerization of methyl methacrylate. Factors such as the reaction temperature and mole ratio of catalyst to initiator, which could affect the ATRP system, were discussed in the paper. The functional end group was characterized via UV-vis and ¹H NMR spectroscopy. The rates of polymerizations exhibited first-order kinetic with respect to the monomer, and a linear increase in the number-average molecular weight with increasing monomer conversion was observed for these initiation systems. The polydispersity indices of the polymer were relatively low (1.07-1.23) up to high conversions. In DMF solution the end-functionalized PMMA decreased its fluorescence intensity in the presence of metal cations (Zn²⁺, Co²⁺, Ni²⁺, Pb²⁺, Mn²⁺, Cu²⁺,Fe³⁺,Ag⁺).(3) A benzothiazole-containing monomer, 4-(2-benzothiazole-2-yl-vinyl)-phenyl methacrylate (BVMA) was synthesized. Atom transfer radical polymerization (ATRP) of BVMA was conducted using BPBVE as an initiator. The obtained poly(4-(2-benzothiazole-2-yl-vinyl)-phenyl methacrylate) (PBVMA) was characterized via ¹H NMR, and chain extension with 4-methacryloxy-hexyloxy-4'-nitrostilbene (HNS) was conducted using PBVMA as the macroinitiator. The homopolymer PBVMA in DMF solution emitted blue fluorescence, and the copolymer PMABE-b-PHNS emitted relatively strong orange fluorescence at about 610 nm due to the intramolecular energy transfer. ATRP of BVMA was also conducted using 2-bromo-2-methyl-propionic acid 4-nitrostilbene-hexyloxy ester (BPNHE) as an initiator. The obtained polymer was characterized via ¹H NMR and the fluorescence changed with increase of number average molecular weight (M_n). The polymer with M_n = 15900 emitted white fluorescence in DMF solution. All the rates of polymerizations exhibited the first-order kinetic with respect to the monomer, and a linear increase in the number average molecular weight with monomer conversion increasing was observed. Most of the polydispersity indices (PDIs) of the polymers were below 1.50.(4) A polymethacrylate derivative,poly(4-(2,5-diphenyl-3,4-dihydro-2H-pyrazol -3-yl)-phenylmethacrylate-co-4-methacryloyloxyazobenzene) [PDPMA-co-PMOAB] was synthesized. The structure of the copolymer was characterized by ¹H NMR. The copolymer combined photoluminescence property and photochemical behavior of both triphenyl pyrazoline and azobenzene moieties in the side-chains. The photoluminescence property of the polymer so obtained could be modified through the photochemical isomerization reaction of the photoactive groups.(5) 2-Bromo-2-methyl-propionic acid 4-benzothiazole-2-ylazo-phenyl ester (BPBE), 2-bromo-2-methyl-propionic acid 4-(6-methoxy-ben zot hiazole-2-ylazo) -phenyl ester (BPMBE), and 2-bromo-2-methyl-propionic acid 4-(6-nitro-benzothiaz-ole-2-ylazo)-phenyl ester (BPNBE) were synthesized and acted as the initiators for the heterogeneous atom transfer radical polymerization of MMA. No obvious third-order nonlinear optical property was observed for the obtained polymers. 4-benzothiazole -2-ylazo-phenyl-methacrylate (BAMA),4-(6-methoxy-benzothiazole-2-ylazo)-phenyl-methacrylate (MBAMA), and 4-(6-nitro-benzothiazole-2-ylazo)-phenyl- methacrylate (NBAMA) were synthesized and acted as monomers for normal radical polymerizatio ns. Third-order nonlinear optical property of the monomers and polymers were studied. 4-thiazole-2-ylazo-phenyl methacrylate (TAMA), 4-benzothiazole-2-ylazo-phenyl-methacrylate(BAMA),2-{4'-[[N-(2-methacryloyl)ethyl]-N-ethyl]phenylazo}-5-nitrothi azole (MANT), and 2-{4'-[[N-(2-methacryloyl)ethyl]-N-ethyl]phenylazo}-6-nitroben zothiazole (MANBT) were synthesized and acted as monomers for normal radical polymerizations. Third-order nonlinear optical property of the monomers and polymers were studied.