Molecular electronic structure and semiconduction in phthalocyanines

MOLECULAR ELECTRONIC STRUCTURE AND SEMIGONDUCTION IN PHTHALOCIANINES

TAI SIB GH

Thesis Submitted to Indian Institute of Technologyl Delhi for partial fulfilment of the Degree of

Doctor of Philosophy 1972

ACKNOWLEDMMENT

The problem of the thesis was suggested by Dr. S.C.Mathur. I wish to express my highest sense of gratitude to him for his constant guidance and interest in the problem. My thanks are due to Dr. A.K.Ghatak for his interest in the work. I am very grateful to Professor P.O.

Lb6wdin whose suggestions for the improvement of my research papers have been very helpful in developing the thesis. I will fail in my duty if I do not acknowledge the various suggestions given by Professor M.Gouterman.

The author is indebted to Professor M.S. Sodha and Professor K.L. Chopra who as Chairman of the Department Provided facilities for the present work. I am also thankful

to Dr. Daroga Singh of I.A.R.S. for putting necessary facilities of his Institute at my disposal.

My thanks are due to Mr. D.C.Singh and Mr. Brijesh Kumar for their manifold helps during the course of the work and to Mes s A.M.Dwivedi, B.M.Bahal, S.L.3ansal, A.Swaroop, G.Bose and H.C.Gupta for their friendly encouragement. Thanks are also due to authorities of Computer Centre,

for providing the facilities to

work.

Behind any academic achievement there are many personalities whose help is needed to provide a favourable atmosphere to work. I should like to specifically mention the name of Shri R.N.Shrivastava, Assistant Director,

Frequency Assignment, A.I.R., who in many ways, other than academic, is responsible for this work. In addition, a long list of my friends can be added to this category.

This thesis could have not been completed but for the painstaking and accurate typing by M. T.N.Gupta and the drawing of the figures by W. N.S.Gupta.

The financial assistance for the work was provided by C.S.I.R., India. This financial grant is

gratefully acknowledged.

Object of the Thesis

Phthalocyanines are one of the most important class of organic photo-and semiconductors. Besides, similarities of their molecular structure with that of

chlorophyll. and hemoglobin, the two most important biological molecules, add to the importance of phthalo- cyanines. Therefore, determination of molecular

electronic structure of phthalocyanines is expected to give valuable informations which may be extrapolated

to get some insight ,into the complex biological molecules.

In addition, the molecular electronic structure is very useful to understand the optical and chemical properties of the molecule. Using molecular orbitals and the X-ray crystal structure, one can obtain the energy band

structure of crystalline solids. It is well known that a detailed knowledge of energy band structure can yield informations about charge carrier transport in solids,

Keeping in mind the importance of the calculations mentioned above the various phthalocyanines have been made a target of such calculations for the present work.

C ONT TS

Chapter Page

Object of the thesis 1

I General Introduction and Synopsis 2 II MoleCular Electronic Structure of 10

metal. phthalocyanines

2.1 Theory of molecular orbitals of 11 metal phthalocyanines

2.2 MOs of platinum phthalocyanine 23

2.3 Discussion 25

2.4 IF-electron charge densities for 27 various phthalocyanines

2.5 Spectra-of metal phthalocyanines 28 III Semiconduction in Phthalocyanines 38

3.1 Introduction

39

3.2 General Theory of band structures 3

!-3 3.3

phthalocyanines

3.5 Energy band structure of PtPc

65

•

3.6 Mobility tensors Oki .) 74

3.7

Tables

93

Cormnonl; used notations

AOs atomic orbitals

Ca--) Zn all the elements from calcium to zinc in 3d-series of the periodic table.

HOMO • highest occupied molecular orbitals

LEMO lowest empty molecular orbitals Phthalocyanine