Photochemical Sciences Ph.D. Dissertations

Photophysical Properties of Metallonaphthalocyanines: Experimental and Theoretical Investigations

Date of Award

2006

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Michael Rodgers

Abstract

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. The nature of the central metal ion plays a crucial role in changing 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 turned to naphthalocyanines coordinated with different metals to investigate central metal effects on photophysical properties.

In this work results are presented on the photophysical properties of the MNc(OBu)8family 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 have been employed along with DFT/TDDFT theoretical examinations. These theoretical results provide a complete picture of the nature and energies of 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.

The H2 and Zn complexes showed formation of the S1(π,π*) state that decayed via fluorescence to the ground state and the intersystem crossing to the T1(π,π*) state. PdNc(OBu)8showed formation (10 ps) of a long lived π-localized triplet state, which decayed with a 0.9 µs lifetime. Compounds with Pt(II), Ir(III), Rh(III) and Ru(II) showed similar behavior with pronounced heavy-metal effects. In NiNc(OBu)8the initially formed S1(π,π*) state deactivated within the time resolution of the instrument to a vibrationally hot T1(π,π*) state. After vibrational relaxation, the T1(π,π*) converts rapidly and reversibly into the 3LMCT(π,dx2-y2) state. The equilibrium state so generated decays to the ground state. The Co(II) complex returns to its ground state via two channels: a trip-doublet state and a (d,d) state. CuNc(OBu)8showed ground state repopulation from a degenerate set of trip-doublet (2T1) and trip-quartet states via a lower-lying set of LMCT states predicted by the TDDFT calculations.

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