Photooxidation of Some Metallocenes in a Polymer Matrix

B Mallik

doi:10.3390/10060708

Abstract

The changes in the electronic absorption spectra (UV-Vis) of some metallocene-doped poly(methyl methacrylate) (PMMA) thin films containing chloroform molecules as impurities were studied after photoexcitation in the nitrogen atmosphere. Photoexcitations were made by monochromatic radiation (using a Xe-lamp source and a monochromator) at an interval of few nanometers in the spectral range 210-750 nm. The changes in spectra were studied as a function of photoexcitation time (duration), amount of metallocene in the film and the amount of chloroform molecules present in the film. Occurrence of photoinduced charge-transfer between some metallocenes and chloroform molecules confined in the PMMA thin films was observed, which indicated photooxidation of the metallocenes in the polymer matrix. Photoresponse in the case of ferrocene derivatives was observed to decrease with the increase in the value of para-Hammett constant for the substituent attached to the ferrocene unit and also with increasing half-wave potential for the ferrocene derivatives. Photoeffects on the metallocenes having different central metal atom were studied and it was noticed that the photoeffects on the metallocenes with "18 valence electrons", as in ferrocene and ruthenocene, favored the occurrence of photoinduced charge-transfer between the metallocene and chloroform molecules present in a PMMA film. The photooxidation of a metallocene in a PMMA thin film resulted in an enhanced photoconductivity of the polymeric film.

Highlights

Ferrocene, bis(cyclopentadienyl) iron: Fe(C5H5)2; abbreviated as FcH in this article; the first synthesized [1] organometallic sandwich compound and its derivatives belong to the general class of compounds known as the “metallocenes”
Recent studies in our laboratory [38,39,40] have shown that photoinduced charge-transfer occurs between metallocenes and chloroform molecules confined in poly(methyl methacrylate) (PMMA) thin films i.e. photooxidation of metallocenes in the presence of chloroform molecules is possible in the PMMA matrix
The difference in the electronic absorption spectrum for PMMA film containing chloroform molecules is shown in Figure 1 (b), which indicates that photoexcitation increases the intensity of the electronic absorption spectrum of PMMA film containing chloroform molecules

Summary

Introduction

Bis(cyclopentadienyl) iron: Fe(C5H5); abbreviated as FcH in this article; the first synthesized [1] organometallic sandwich compound and its derivatives belong to the general class of compounds known as the “metallocenes”. Because of the various important applications of metallocenes in technological fields and for their important electrical properties, a program was undertaken in our laboratory to study the possibility of photooxidation of metallocenes in a polymer matrix (film) containing halocarbon solvent molecules. To examine the photooxidation of metallocenes present in the solid polymer matrix containing halocarbon solvent molecules as impurities, a program was undertaken to study spectroscopically the effects of irradiation (UV-Vis) on the metallocene-doped poly(methyl methacrylate) thin films prepared from solvents chloroform and benzene and mixture of these solvents. Recent studies in our laboratory [38,39,40] have shown that photoinduced charge-transfer occurs between metallocenes and chloroform molecules confined in PMMA thin films i.e. photooxidation of metallocenes in the presence of chloroform molecules is possible in the PMMA matrix In this present article the overall results on the topic are discussed

Results and Discussion

Conclusions

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