3.Fluorescence Detected Magnetic Resonance of Triplet States Spectroscopy and Photophysics of Self-Organized Zinc Porphyrin Nanolayers.

摘要

Fluorescence detected magnetic resonance (FDMR) has been applied to approx 25-nm-thick porphyrin films,containing ordered domains of zinc tetra-(p-octylphenyl)-porphyrin (ZnTOPP) spin-coated onto quartz slides.Illuminating the films at 1.4 K with 457.9-nm light from a continuous wave Ar~+ laser produces at least two different,Jahn-Teller-distorted,ZnTOPP triplet species,labeled i and ii.Microwave-induced magnetic resonance of i and ii in the absence or presence of an externally applied magnetic field affects the fluorescence intensity of ZnTOPP,thus allowing FDMR.For triplet species i,formed in films spin-coated from toluene solution,the zero-field splitting (ZFS) parameters were determined as D = (316.9 +- 0.1) x 10~(-4) cm~(-1) and E = (32.0 +- 0.5) x 10~(-4) cm~(-1).By exposure of the spin-coated films to chloroform vapor at room temperature,triplet i is converted into species ii,with D = (295 +- 3) x 10~(-4) cm~(-1) and E = (121 +- 3) x 10~(-4) cm~(-1).For the excited triplet state of ZnTOPP in a toluene glass,ZFS parameters with values of D = (295 +- 1) x 10~(-4) cm~(-1) and E = (91 +- 1) x 10~(-4) cm~(-1) are found.From a combined study of the FDMR- and microwave-induced fluorescence spectra,i and ii are identified as unligated and ligated ZnTOPP triplet species,respectively.From the asymmetrically shaped zero-field FDMR signals of i,we conclude that the local crystal field perturbations of the stacked molecules are anisotropic.The FDMR results of the ZnTOPP films are compared with those for a film of zinc tetraphenylporphyrin (ZnTPP),which lacks the octyl substituents,and therefore is nonordered.Upon illumination,the ZnTPP films contain only a single,ligated,triplet species with ZFS parameters very similar to those of ligated ZnTOPP.At approx 5 K,the lifetime of triplet i is considerably shortened compared to that of ZnTOPP in a glass at the same temperature.