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Photophysical properties of metallonaphthalocyanines experimental and theoretical investigations /

by Soldatova, Alexandra V.

Abstract (Summary)
Michael A. J. Rodgers, Advisor To date the photothermal effects studied in this laboratory have employed tetrapyrroles with first row transition metal centers as exogenous photosensitizers and this, in turn, has sponsored research efforts into the excited state dynamics of such compounds with the intent to formulate an understanding of how such dynamics depend on molecular characteristics. The nature of the central metal ion plays a crucial role in changing the electronic structure and the excited state dynamics of the compounds. Recently there has been increasing interest in metallonaphthalocyanines as photothermal sensitizers for tumor therapy purposes due to the promising results obtained for Ni(II)-5,9,14,18,23,27,32,36-octabutoxy-2,3-naphthalocyanine, NiNc(OBu)8. Within this context our attention has now turned to naphthalocyanines coordinated with different metals to investigate central metal effects on photophysical properties, and in what follows the results of theoretical and photophysical experiments are presented and discussed. In this work results are presented on the photophysical properties of the MNc(OBu)8 family with Co group and Ni group metal ions together with Ru(II), Cu(II) and Zn metal ions and a free base analog. Transient absorption spectrometries with fs and ns resolutions have been employed along with DFT/TDDFT theoretical examinations. These theoretical results provide a complete picture of the nature and energies of all electronic states, allowed and forbidden, between the ground and excited states. The two approaches, experimental and theoretical, are brought together to generate a detailed understanding of the sequence of events that follow photo-excitation and to gain an insight on central metal effects on the photophysical properties. iii The investigation has been carried out with the H2 and Zn complexes as benchmark compounds. These showed the formation of the singlet (?,?*) state that decayed via fluorescence to the ground state and the intersystem crossing to the triplet (?,?*) state. The compound with Pd(II) as the central metal showed the formation (10 ps) of a long lived ?-localized triplet state, which decayed with a 0.9 ┬Ás lifetime and, in the presence of O2, the formation of singlet oxygen via an endoergic energy transfer process. Compounds with Pt(II), Ir(III), Rh(III) and Ru(II) showed similar behavior with pronounced heavy-metal effects. In NiNc(OBu)8 the initially formed S1(?,?*) state deactivated within the time resolution of the instrument (200 fs) to a vibrationally hot T1(?,?*) state. The quasi-degeneracy of the S1(?,?*) and 3(dz2,dx2-y2) states allows for fast intersystem crossing to occur. After vibrational relaxation (ca. 2.5 ps lifetime), the T1(?,?*) converts rapidly (ca. 19 ps lifetime) and reversibly into the 3LMCT(?,dx2-y2) state. The equilibrium state so generated decays to the ground state with a lifetime of ca. 500 ps. The Co(II) complex was shown to return to its ground state via two competing channels: a trip-doublet state that decayed with a 1 ps lifetime and a (d,d) state that repopulated the ground state surface with a 15 ps lifetime. The TDDFT results indicated that the (d,d) state arises from the transition from a fully occupied metal d? orbital to a close-by partially occupied metal dz2 orbital, resulting in a low energy state that has a short lifetime. CuNc(OBu)8 showed ground state repopulation that was completed within a few ns from a degenerate set of trip-doublet 2T1 and trip-quartet 4T1 states via a lower-lying set of LMCT states predicted by the TDDFT calculations. In all, the results of the present investigation reveal fundamental background knowledge of the electronic factors in the photophysical properties of metallonaphthalocyanine macrocycles. To my parents iv v
Bibliographical Information:

Advisor:

School:Bowling Green State University

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:phthalocyanines photochemistry picosecond pulses

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