Fluorescence and Viscometry Studies of Poly(4-hydroxystyrene) in Solution

Abstract

ABSTRACT:Fluorescence and viscosity of dilute solution of poly(4-hydroxystyrene) (PHS) were measured in methanol in the temperature range 5 to 55°C. The fluorescence spectrum of PHS showed two emission bands at around 308 nm and 356 nm, corresponding to the monomer and the excimer bands, respectively. From the temperature-dependent fluorescence measurements, a plot of the excimer to monomer intensity ratio Idllm versus temperature was obtained, which shows double lines with positive slopes crossing at ca. 35°C. From temperature-dependent viscosity measurements, a plot of the limiting viscosity number ['1] versus temperature was obtained, which shows double lines with negative slopes crossing at ca. 40°C, above which the slope was decreased. These results indicate that there is stronger solvation of solvent molecules to polymer coil at temperatures below ca. 35---40°C, arising from hydrogen bond formation between PHS and methanol molecules.KEY WORDS Poly(4-hydroxystyrene) I 4-Ethylphenol I Excimer I Fluorescence I Polymer Conformation I Polymer Solution I Temperature Dependence I Viscosity I Many vinyl polymers with aromatic chromophores exhibit intramolecular excimer fluorescence in solution. 1 Excimers are excited-state complexes formed by a couple of chromophores placed face to face at a short distance. The formation of an excimer is due to assoc1atwn of two aromatic groups separated by three carbon atoms along the chain, one of which has been electronically excited. 2 It is characteristic for excimer fluorescence to appear in a considerably lower energy region than monomer fluorescence and· to have no mirror image relation to the absorption spectrum. The intramolecular excimer formation for vinyl polymers is governed by both the conformation and configuration of the chains.Excimer formation has been observed in polystyrene 3 -5 and its derivatives such as poly(tX-methylstyrene ), 6 • 7 and poly( 4-methylstyrene),8 but not in such analogous polymers as poly(4-chlorostyrene) and poly(4-bromostyrene ). 9 Jiang et a!. 9 showed that the fluorescence spectrum of poly(4-hydroxystyrene) (PHS) has a vibrational structure and cannot be attributed to the formation of excimer. They insist that the presence of bulky hydroxyl substituents in PHS does not allow parallel arrangement of aromatic rings along with the polymer chain, which is a necessary condition for the excimer formation. However, when Figure 3 in ref 9 is examined, their interpretation does not seem consistent with the view that the monomer fluorescence spectrum is the single mirror image of the absorption spectrum. The fluorescence spectrum in the figure shows the anomalous fluorescence emission band at the longer wavelength than that where the fluorescence emission band corresponding to the mirror image of the absorption spectrum appears. The lower energy band of this fluorescence spectrum 1223

Formation of Intramolecular Poly(4-hydroxystyrene) Dimer Radical Cation

“…This band was quenched by CCl 4 . The monomer and excimer bands of PHS have been reported to appear at 308 and 356 nm in methanol solution, respectively . The emission maximum at 390 nm is considered to be due to the excimers of PHS.…”

Synthesis and self-assembly of a carborane-containing ABC triblock terpolymer: morphology control on a dual-stimuli responsive system

“…In the fluorescence measurements, P5-10 samples showed two distinctive fluorescence bands: One around 308 nm attributed to emission from single repetitive units of PHS and a broad band around 350 nm resulting from excimer emission of PHS. 44 However, the increase in pH to pH > pKa(PHS) causes an abrupt loss of fluorescence, which proves that PHS block is the main contributor to the fluorescence signal. This fluorescence was restored by lowering the pH to pH < pKa(PHS) (Figure 4c).…”

“…After deboronation, PHS and PSC blocks undergo a micro-phase separation in the core, which allows the formation of a more extensive hydrogen bond network among PHS chains, thus increasing the rigidity of the PHS compartments and the fluorescence intensity. 44 Accordingly, we added a small amount of THF to the reaction mixture to increase core plasticity and to promote the rearrangement of PSC domains. In this case, fluorescence intensity increased by 84% (after removal of THF) (Figure 4c and Figure S2).…”