Ph.D. Thesis
Title Physical chemical and Raman spectral investigation
of phthalocyanines of copper and aluminum and their thin films
Advisers Dr. Boris A. Kolesov and Prof. Igor K. Igumenov
Thesis Committee Prof. F.A. Kuznetsov; Dr. Buyanova L.M.
Essay
The phthalocyanines have been a subject of a vast amount
of study, both theoretical and experimental. They have been studied
for their possible use as dyes and catalysts. Because of their similarity
to chlorophyll and haemoglobin, they have been extensively studied
as model compounds in biochemistry. However, the most exciting application
of phthalocyanines is that they represent one of the most promising
materials for future molecular opto-electronic devices. In spite of
advances in metal phthalocyanine chemistry, till present there are
no reliable experimental data on thermal properties of phthalocyanines
in condensed and gas phase, and on methods to characterise their films.
The present investigation is aimed at the solution of
the following scientific problems: first, investigation of thermal
properties of free phthalocyanine (a, b-H2Pc)
and its complexes with copper (a, b-CuPc)
and aluminium (AlClPc, AlFPc, (AlPc)2O); second, the development
of scientific foundations for the preparation of oriented films on
various substrates; third, the development of a new method for the
determination of phthalocyanine films orientation by means of Raman
spectroscopy.
The following results were obtained when solving the
listed problems.
1. Copper and aluminium phthalocyanines and free phthalocyanine
have been synthesised and characterised using elemental analysis,
vibrational spectroscopy, X-ray phase analysis. On the basis of the
data obtained by means of high-temperature mass spectrometry, differential
thermal analysis and thermogravimetry in vacuum, the regimes of purification
and separation of phthalocyanines by gradient sublimation in a vacuum
have been proposed.
2. The composition of the gas phase above the free phthalocyanine
and its complexes with copper and aluminium has been studied by means
of high-temperature mass spectrometry. It has been stated that phthalocyanine
decomposition does not occur in the gas phase within the temperature
range studied (up to 700 oC). The vapour pressure of these
phthalocyanines has been determined as a function of temperature by
the Knudsen effusion method, in which the rate of effusion of the
equilibrium vapour through a small orifice was measured. Thermodynamic
parameters of phthalocyanine vaporisation (DHoT
, DSoT
) have been obtained using experimental data P=f(T). These
investigations for phthalocyanine and aluminium phthalocyanines have
been obtained for the first time.
3. On the basis of experimental data obtained, the regimes
of phthalocyanine film deposition have been optimised. By means of
vacuum organic molecular beam deposition, oriented polycrystalline
films of copper phthalocyanine have been obtained. The films thus
obtained have been studied by means of Raman spectroscopy and X-ray
diffraction. It has been stated that at the substrate temperature
within the range 20-160 oC, polycrystalline films are formed,
their structure corresponding to the a-modification of copper phthalocyanine,
while at the temperature of 180-185 oC, b-modification
is observed. 4. In order to develop the technique of the determination
of phthalocyanine film orientation the detail analysis of the Raman
spectra of CuPc was performed. The normal coordinate analysis for
all in-plane gerade modes of copper phthalocyanines (CuPc) has been
carried out. We at first have determined the symmetry of modes based
on the polarized Raman spectra of the oriented CuPc single crystal
and its solution. So far the calculations of phthalocyanine spectra
were not confirmed by the data for isotopically substituted compounds.
In the present work, the isotopic frequency shifts upon 15N
substitution for nitrogen atoms in CuPc have been measured. These
experimental data enabled us to confirm the calculation and to discuss
some details of normal vibrations of CuPc molecule. It was shown that
the bands at frequencies below 200 cm-1
correspond to the crystal modes. The bands at frequencies above 200
cm-1 are assigned to the internal
molecular vibrations.
5. In this work, we have suggested the general approach
to the analysis of the orientation of phthalocyanine thin films by
the method of Raman spectroscopy, using the films of a
and b copper phthalocyanine as an example.
It has been shown that the orientation of thin films may be determined
using the analysis of crystal modes as well as internal molecular
vibrations. The determination of the orientation by the analysis of
external modes is based on the comparison of b-CuPc
single crystal spectra recorded at various polarization of incident
light with the spectrum of film. The crystal modes are directly connected
with crystal structure determining their number and symmetry. However,
given approach does not apply for the analysis of the films of compounds
with unknown crystal structure. In this case, the analysis of internal
molecular vibrations is more a general and universal method. The principle
of the approach based on the analysis of internal molecular vibrations
is the following. The information on structural features of any film
(oriented, partially oriented, disordered) is contained in the matrix
elements of scattering tensors of individual type of vibrations. In
order to obtain such information, it will suffice to measure the
Iii / Iij ratios ( Iii
/ Iij is the ratio of average values of Raman intensities
in parallel and cross polarization of incident and scattering light)
for each vibration types. It was determined that the CuPc films are
oriented so that the XY plane of microcrystallites is parallel to
the substrate surface, the molecule planes in a-CuPc
film forming an angle of about 29o with the normal to the
substrate surface. The molecules in b-CuPc
film form an angle of about 40o.
6. The investigation of the orientation of the polycrystalline
CuPc films deposited on the substrates from quarts, aluminium, copper,
silicon, MoS2, NaCl has been carried out using the proposed
techniques. It was stated that the films deposited on above mentioned
substrates at identical conditions had the same orientation. The results
are of theoretical importance as well as of practical use. The results
of the measurements of the temperature dependence of phthalocyanine
saturated vapour pressure within rather wide temperature range allowed
to obtain reliable quantitative information that served as a basis
to develop optimal regimes of the deposition of thin phthalocyanine
films by OMBD. The application of the technique to determine film
orientation proposed in the present work is not limited to the analysis
of phthalocyanines. This approach can be used successfully to analyse
various molecular films deposited onto any substrates. It may be especially
important in determining the orientation of polymers in Langmuir-Blodgett
and liquid crystal films, which are extensively studied today.