Raman spectra phthalocyanines

Journal of Molecular Structure, 143 (1986) 131-134

131

Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

RAMAN SPECTRA

OF PHTHALOCYANINES

R. AROCA Department

of Chemistry,

University

of Windsor,

Windsor,

Ontario

N9B 3P4(Canada)

ABSTRACT Raman spectra of amorphous phthalocyanine thin films have been studied. Theoretical and experimental correlations in polarization ratios are applied to vibrational assignments of symmetry species and to the problem of molecular orientation in thin solid films.

INTRODUCTION Phthalocyanines(Pc)

are macrocyclic

ring formed by four isoindole increasing stability

interest

in these organic

and outstanding

molecules

containing

units linked by aza nitrogen materials

photoelectrical

inner

The

is due to their high thermal

properties:

their applications

in photovoltaic

optical

in the red that could be modulated

absorption

a 16 menber

atoms.

photoconductivity,

cells', and photoelectrochemical

and

cells';

for practical

applications

in xerography3, storage

and their potential application as a high density optical 4 material . For most applications PC are used as thin solid films where

the material several

forms an amorphous

polymorphic

are now intensively properties

studied3.

perpendicular between

molecular

molecules6.

plane was reported

The angle between to be 30 degrees.

films.

generalized

occurrence

depolarization of symnetry results

the interpretation

More recently,

is a powerful

In a series of reports7, we

under the assumption

in PC films we have measured

of molecular

almost

interactions

Raman spectroscopy

of a number of PC

that "stacking"

is a

and calculated the vibrational

orientation.

for CuPc films are discussed.

0022-2860/86/$03.50

For instance,

n electronic

of the Raman spectra(RS)

and the problem

of

the column axis and the

ratios in thin films to investigate

species

in the understanding

macromolecules.

interactions.

and working

in

aggregation

solid films is related to the

plane due to a strong

tool in the study of intermolecular have presented

between

of induced

have been shown to pile up in a direction

to the molecular

adjacent

question

of these amorphous

of the interactions

in CuPc films CuPc molecules

It has been shown that PCS exist

, and the possibilities

The fundamental

and characteristics

nature and magnitude

solid.

modifications5

0 1986 Elsevier Science Publishers B.V.

assignment

Here, the

132 RESULTS AND DISCUSSIONS PC films were prepared

by vacuum evaporation

NESA (tin oxide glass) plates

Inficon XTM quartz microcomputer were

in a Varian NRC 3115 system at a pressure

Film thickness

5 x lo-7 Torr.

(typically

crystal oscillator.

controlled

system

on a 164 Ar+ laser.

polarizer

and scrambled

Experimental

described

conventiong'lO.

incidence

Scattered

have P polarization. be measured

Porte's

Illumination

along the x-axis.

is always

The plane of

the normal to the thin solid film and the incoming plane.

to the plane of incidence parallel

using a linear

following

plane is the xz-plane.

laser beam) is also the scattering

light polarized

measurements

model 310-21)

the Spex 1403 spectrometer.

z-axis and observation

(plane containing

(y-direction)

light was analyzed

of with an

using a

Polarization

(Spectra Physics

results are described

The scattering

along the positive

elsewhere8.

rotator

before entering

and theoretical

100 to 200 nm) was monitored

Raman shifts were analyzed

carried out using a polarization

mounted

from a tantalum boat onto

(x-direction)

Therefore,

in this geometry:

Light polarized

perpendicular

is said to have S polarization, to the plane of incidence

there are four polarized

and

is said to

components

that can

z(yy)x = SS, z(yz)x = SP, z(xy)x = PS and

z(xz)x = PP. PC metal complexes

may belong

to a C4v point group (in this case the metal

atom is located above or below the molecular when

the metal is on the plane.

are Al(Alg), summarized

Bl(Blg),

B2(BZg)

by Loudon"

The symmetry

and E(Eg).

are identical

consecutive

systems

orthogonal

of the molecular angles as defined

for both groups.

transformation

(molecular,

by Golstein'*

matrices

(a detailed

of two angles:

account

convention

of calculations

ratios(DR)

surface angle B

.

all four polarized

A similar calculation

Eulerian

of

and applications

to

Kamitsos

of AgTCNQ

trigonometric

angle 0 and laser beam-normal

A typical calculation

components

the components

publication).

are found to be simple

This angle is experimentally

the

There are

frame.

in their treatment

the molecular-substrate

ratios

and two

the elements

type is shown in figure 1 for three different

of the B angle. measured

to the laboratory

PCS will be given in a separate

The depolarization

to the substrate

and laboratory)

were used to express

tensors

PC films in which

are needed to transform

derivatives

and Risen13 have used a different

symmetry

derivative Depolarization

for oriented

substrate

transformations

polarizability

a number of metallated

functions

that are Raman active

plane forms an angle 6 with the plane of the substrate.

three coordinate

films.

species

Polarizability

(SP/SS, PP/SS and PS/SS) can be calculated molecular

plane), or to a D4h point group

values

determined,

for B equal

for the Al(A1g) (45, 60 and 75)

and we have

to 45, 60 and 75 degrees.

is given in figure 2 for Bl(Blg)

type vibration.

133 Polarized

spectra

of a CuPc film (ZOO nm) excited The intensity

are shown in figure 3.

A comparison

a 0.5 factor. produces

the following

component

no significant (ii) Calculated would

the 514.5nm

of the SS component

of calculated

correlations.

is independent

with

i) Derived

changes were observed

formulae

indicate

DRs

that the SS

Experimentally,

at B = 45, 60 or 75'.

vibrations

Experiment

less than 0.7.

obtained

types.

for the SS component

DRs show that only totally symmetric

always have a DR value

has been reduced by

and experimentally

of the angle 8 for all symmetry

laser line

(A, or Alg)

reveals that in the -1 -1 with 1339cm , 1528cm

region given in fig. 3, there are only three vibrations -1 band of the SS spectrum is Notable the 1339cm low DR values. -1 The SP and PS when the scattered light is not analyzed. observed at 134lcm -1 , a clear indication that the 1339 band is a spectra show a band at 1344cm consistently

totally symmetric

vibration,

while

the 1344 band is most probably

type since DRs for SP and PS are similar. observed

for a number of vibrations,

symmetric

type.

For instance,

iii) DR values greater

allowing

their assignment

the band at 1484cm-'

substrate

to a non-totally

type vibration

Preliminary

results

with a molecular

for a series of PC films seems to support

made here for DR calculations in PC films.

problem of solvent

Presently,

induced

we are applying

aggregation3

the

and the idea that RS are sensitive

which

polarization

seems to increase

studies

Figura 1

F1sju1-02 1.

23.0 45.0 Idol-submtrata

87.0 angle

g!Ao

to

to the

the orientation

in thin films.

1.0

DR values

These values agree well

angle of 35".

assumptions "stacking"

DR for an E(Eg) symmetry

than 0.7 are

has the following

at f3 = 45": SP/SS = 2.8, PP/SS = 2,3 and SP/SS = 2.7. with calculated

a Bl(Blg)

134

Figure 3 Qoo. CuPc

200nm

Film c-1528

225~-

1200.0

1325.0

1450.0 Wavonumbare

1575.0 (cm-l)

170

REFERENCES

6 7

! 10

R-0. Loutfy, J.H. Sharp, J. Chem.Phys., 71 (1979) 1211-1217. A.J. Bard, L.A. Schechtman, D.R. Dininny, B.L. Wheeler, G. Nagasubramanian, M.E. Kenney, J.A.C.S., 106 (1984) 7404-7410. R.O. Loutfy, A.M. Hor, G. Dipaola-Baranyi, C.K. Hsiao, Photographic SC. and Engineering (in press). P. Kivits, R. de Bont, J. van der Veen, Appl. Phys., A26 (1981) 101-105. C.H. Griffiths, M.S. Walker, P. Golstein, Mol. Cryst. Liq. Cryst., 33 (1976) 149-170. T. Kobayashi, Y. Fujiyoshi, N. Uyeda, Acta Crys., A38 (1982) 356-362. C. Jennings, R. Aroca, A.M. Hor, R.O. Loutfy, J. Raman Spectrosc., 15 (1984) 34137. R. Aroca, P. Cook, Am. Lab., 16 (1984) 138-140. T.C. Damen, S.P.S. Porto, B. Tell, Phys. Rev., 142 (1966) 570-574. J.C. Decius, R.M. Hexter, Molecular Vibrations in Crystals, MC. Graw Hill New York, 1977, pp. 169. Inc., R. Loudon, Adv.Phys., 13 (1964) 423-482. H. Golstein, Classical Mechanics, Addison-Wesley, Massachusetts, 1950, pp. 107. E.1: Kamitsos, W.M. Risen, Jr. J. Chem. Phys., 79 (1983) 477-482.

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