Pyrene is a useful molecular probe due to its relatively long excited state lifetime (t1/2 ≈ 100 ns), the III/I ratio in the emission spectrum that is an indication of the medium polarity, and excimer formation that can be used to assess the medium rheological properties. Pyrene has low solubility in water (0.135mg/L), which limits its usefulness as a probe in high polarity media. 1-hydroxymethylpyrene has slightly higher solubility in water because of a CH2OH group. The aliphatic carbon located between the pyrene ring and the hydroxyl group significantly preserves the useful photophysical properties of pyrene. Adding two methanol groups may increase the solubility in water while preserving the useful photophysical properties of pyrene. To test this hypothesis, 1,6 bis(hydroxymethyl)pyrene was photophysically characterized. It was found that the addition of CH2OH groups incrementally caused a bathochromic shift in absorbance. The peak corresponding to 0S→2S transition shifts from 334nm for pyrene to 341nm and 348nm for hydroxymethylpyrene and 1,6 bis(hydroxymethyl)pyrene, respectively. The observed shifts indicate that the excited electron interacts weakly with the oxygen atoms in the methanol group. The 0S→1S transition remains symmetry forbidden for hydroxymethylpyrene, while this transition probability for 1,6 bis(hydroxymethyl)pyrene increases an order of magnitude with respect to that of pyrene. Due to the stronger coupling between the excited electron and the oxygen atoms the fine structure in the emission spectrum of 1,6 bis(hydroxymethyl)pyrene is lost-i.e. this molecule cannot be used as a lumiprobe to assess a medium polarity. Its rate constant for the inherent unimolecular fluorescence decay in water was found to be 3.01 × 106 s-1. Counterintuitively, the solubility in water of 1,6 bis(hydroxymethyl)pyrene was found to be lower than that of pyrene in water. The photophysical properties of 1,6 bis(hydroxymethyl)pyrene in solvents of low polarity will be reported as well.

Effects of methanol group(s) on the photophysical properties of hydroxymethylpyrene and 1,6 bis(hydroxymethyl)pyrene

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.