PHOTOPHYSICAL BEHAVIOR OF ZINC(II) TETRAPHENYLPORPHYRIN IN HIGHLY CONSTRAINING MICROENVIRONMENTS - ANOMALOUSLY LONG-LIVED EXCITED-TRIPLET IN THE HYDROPHOBIC CLUSTERS OF AMPHIPHILIC POLYSULFONATES

A small amount of zinc(II) tetraphenylporphyrin (ZnTPP) was covalently incorporated into sodium polysulfonates modified with cyclododecyl (Cd) (60 mol %) or lauryl (La) (61 mol %) groups. The ZnTPP species are confined within the hydrophobic clusters in the amphiphilic polysulfonates in aqueous solution. In the Cd cluster, the ZnTPP chromophores exhibited unusual photophysical behavior, including delayed fluorescence with an anomalous spectral pattern, strongly blue-shifted phosphorescence, and extraordinarily long lifetime of the triplet-excited state in aqueous solution at ordinary temperatures. Temperature dependencies of the delayed emissions and the triplet decays imply that the ZnTPP species are ''pinned down'' to constrained configurations in the Cd duster, leading to the unusual photophysical behavior. The highly constraining microenvironment in the Cd cluster tends to be loosened in the temperature range 60-80 degrees C, and the pinning down effect vanishes at >90 degrees C. No such unusual photophysical behavior due to highly constraining space was recognized for the La cluster.