Monosubstituted derivatives of pyrene: Comparison of their spectral behaviour in solution and in polymer matrices

Abstract

Spectral properties of monosubstituted derivatives of pyrene were compared in low viscosity solvents such as cyclohexane, chloroform, and methanol, in high viscosity solvents such as heptadecane and polybutene oil, in glassy polymer matrices above T g (atactic polypropylene) and below T g (polystyrene polymethyl methacrylate, polyvinylchloride), and in semi-crystalline low density polyethylene. The derivatives under study were: 1-pyrenylmethanol (I), benzyl-(1-pyrenylmethyl) ether (II), di(1-pyrenylmethyl) ether (III) and 4-(1-pyrenyl)butyl-(1-pyrenylmethyl) ether (IV). Absorption spectra of these probes were not influenced by environment. Emission spectra of III exhibited exclusively excimer emission in low viscosity solvents. Probe IV yielded mainly monomer emission. In viscous solvents and glassy polymer matrices above and below T g, as well as in semi-crystalline polyethylene, monomer emission was exclusively observed for all probes. Distinct differences were observed in emission decay curves. Probes derived from pyrene with a bulky substituent exhibited biexponential decays with a short component (∼10 ns) in viscose solvents and polymer matrices. In semi-crystalline polyethylene, the decay of monomer emission of all probes was monoexponential with a lifetime around 200 ns.