Optical spectra of Ni porphin, Pd porphin and free base porphin in single crystal triphenylene

Acts, Vol. 32A, pp. 1083to 1088. Pergamon Press,1976. Printedin Northern Ireland

Spectrochimica

Optical spectra of Ni porphin, Pd porphin and free base porphin in single crystal triphenylene* JOSEPH BORANDY and BORIS F. KIM Applied Physics Laboratory, The Johns Hopkins University, 8621 Georgia Avenue, Silver Spring, MD 20910, U.S.A. (Received 27 May 1975) Abstract-Polarized optical absorption spectra and luminescence spectra of palladium porphin, nickel porphin, and porphin free base doped into triphenylene host crystals have been obtained. The da metalloporphin spectra obtained hers allow a aomparison to be made with other metalloporphin spectra reported previously from this laboratory and suggest a general description of the polarized absorption spectra of metalloporphins in this host. The observation of many spectral lines which ocour at the same wavelength in absorption and fluoresoencesuggests thet bend I of free base porphin may be of greater complexity than previously thought. INTRODUCTION

and only absorption

in Nip.

Luminescence

ob-

Most spectroscopic studies of porphyrins have been

served in the NiP sample turned out to be a CUP

done either of solutions or of polycrystalline

impurity.

ples of porphyrins (usually

called

Shpol’skii

primary disadvantages polarization

sam-

spectra).

and VO while the high resolution FBP spectra are

of the

of special

of these methods is that the

characteristics

be obtained directly.

One

interest

in light

of recent

resonance

Raman spectra of FBP [7] which indicate that band

of the spectra cannot

This leboratory

These studies allow the d3 metdlopor-

phins to be compared with each other and to Zn, Cu

in frozen normal hydrocarbons

IV contains at least 3 pure electronic transit’ions.

has recently

reported optical spectra of zinc porphin (ZnP) [l], copper porphin (VOP)

(CUP) [2], and vanadyl

[2] in host crystals

material

is crystalline

EXPERIMENTAL

porpbin

of triphenylene.

This

at room temperature

and

polarized spectra were easily obtained. Shpol’skii

or quasiline absorption

and lumine-

scence spectra of free base porpbin (FBP) palladium reported

porphin by

(PdP)

Russian

[3] and

[4] at 77OK have been

workers.

EAS~WOOD and

GOUTERMAN [5] obtained phosphorescence

spectra

of PdP in nonane and report &,, and &?Iabsorption peaks

for NIP

glycolate). cence

of

in MPEG

(methylphthalylethyl-

CALLIS et aE. [6] also observed fluoresPdP

in

MMA

(methylmetbacrylate).

Quasiline spectra of nickel porphins

(Nip)

do not

appear to have been published. As part of our continued

effort in the spectros-

copy of porphyrins, we have obtained the polarized optical absorption spectra, a.s well as luminescence spectra, of FBP and the d* metalloporphins, and Nip, stals.

incorporated

Absorption

in FBP,

into triphenylene

PdP

host cry-

and fluorescence were observed

absorption

and phosphorescence

* Work supported by the Naval Sea Command under contract KO0017-72-C-4401.

in PdP, Systems

The absorption and luminescence spectra were taken photographically on e one-meter, f/8 JarrellAsh Spectrograph with a first order resolution of 0.15 A and dispersion of 7.5 &mm and on 8 60 cm, f/8 spectrograph having resolution and dispersion of 0.5 A and 16 &mm, respectively. Kodak contrast process film and high speed i.r. film were used. The spect,ra, of iron and neon were used for wavelength measurements. Luminescence was excited with a GE AH-6 mercury discharge lamp. Triphenylene is an orthorhombic crystal with a space group of P2,2,2, [8]. The crystals grow in the form of needles with the long dimension being the crystallographic c-axis. Small crystals of triphenylene doped with FBP, PdP, and NIP having good optical quality were grown by evaporation techniques. The crystals were typically 1 mm X 1 mm in cross section and 6 mm in length. The porphin compounds were purchased from the Mad River Chemical Company (now defunct). The crystals were immersed directly into liquid nitrogen or liquid helium for the low temperature observations. The c-axis of the crystal was vertical and ?r and o polarization means that the electric vector of the incident light wss parallel and perpendicular to c, respectively. Single crystal samples were used in all cases but polarized luminescence spectra were not taken.

1083

J. BOHANDY and B. F. Kriv~

1084 RESULTS

Q.

(a) Free base porphin single crystals

proximately

Many

was considerable.

125 sharp absorption

served in the vicinity

Ap-

lines were ob-

of bands I and II.

While

the cm-’

strongest

P-polarized

1325 cm-l,

graphic

sharp absorption lines were polarized with respect to the c-axis of triphenylene.

Furthermore,

were several lines on the long wavelength band I which were predominantly Approximately

there side of

o-polarized.

region between

of PdP

exposures

6172 A and

while

1281

vibration.

in MMA,

at 4.2’K

fluorescence in PdP/TP.

In

long photo-

did not

reveal any

No attempt was made to

observe delayed fluorescence at room temperature. A

relatively

strong

served in NiP/TP

110 sharp fluorescence lines were

vibrations

e-polarized

in are

CALLIS et al. [B] report room tempera-

of bands III

but not all, of the

and 1411 cm-l

in

respectively.

Although

ture fluorescence

Many,

prevalent

these same vibrations are 1014, 1352 and

only broad, diffuse bands were seen in the region and IV.

lines are apparent vibration

1028 cm-l

is the strongest

NiP/TP,

these sharp lines had a width on the order of 1 A,

seen in the spectral

vibronic

with a 385 cm-r

both polarizations.

The increase in spectral resolution with the use of doped

band.

PdP/TP

comparison

phosphorescence

at 4.2’K.

was

However,

with the phosphorescence

ob-

a careful of CuP/TP

[2] showed that the NIP spectrum was actually a

7158 A. Obvious multiplets were not observed in CUP impurity. PdP/TP exhibited a strong phosthe single crystal sample, contrary to SEVCE~ENEO phorescence at 77OK and 4.2%. Figure 3 shows et al. [3] who report triplets in the quasiline absorptypical spectra. Only broad bands were seen at 77’K tion snd fluorescence spectra of FBP in octane. with the peaks of these bands at vibretional freNote, however, that triplets were observed in the

quencies which correspond to vibrations reported

fluorescence spectra of polycrystalline

for PdP in octane [4].

FBP/TP

[9].

Furthermore,

samples of

there are slight dis-

O-Ophosphorescence

A 180 cm-l splitting of the band at15,282

cm-1 (6642 A)

crepancies in fluorescent wavelengths

of the single

at 77OKwas not observed. Such a splitting was seen

crystal

of FBP/TP

in PdP in nonane by EASTWOOD and GOUTERMAN

and

the

and

polycrystalline

polycrystalline

samples

samples

had

somewhat

[5].

At 4.2’K,

multiple&

consisting of sharp lines

in the spectrum

in place of the bands.

broader lines. This could be due to a concentration

appear

effect.

There appears to be a quintet of lines (separated

The most interesting and important

point to be

by approximately

19, 32, 38 and 13 cm-l)

which

made regarding the free base specta can be seen in

repeat at 397, 805, 1334, 1605 and 2002 cm-r from

Fig.

the O-O

1 which shows absorption and fluorescence One sees that many

spectra in the region of band I.

of the lines (28 to be exact) occur at the samewavelength in absorption

and fluorescence.

Assuming

transition

lines are week, Tables

1 and 2 list the absorption

phorescence

singlet electronic state, this implies that all of these

with the FBP/TP,

lines are from

not been tabulated.

pure electronic

transitions.

The

Some of the

and are not shown in

Fig. 3 nor listed in Table 2.

that fluorescence occurs from the lowest excited

presence of these lines made it very difficult to pick

at 15329 cm-‘.

however,

lines of PdP/TP

and

and phos-

NiP/TP.

As

many of the weaker lines have A complete

list is available

upon request.

out vibrational frequencies because of the ambiguity in the O-O

transition.

The

stronger

and fluorescence lines of FBP/TP Tables

1 and 2.

absorption

DISCUSSION

absorption

are tabulated

in

Transitions which occur in both

and fluorescence are marked

with an

asterisk.

Figure 4 shows a “stick” PdP/TP

and NiP/TP,

CuP/TP

and VOP/TP

The polarized

which were reported previ-

NiP in triphenylene (PdP/TP are shown features

[l, 21. Both Pd and Ni

have ds electron configurations absorption

in Fig.

2.

spectra

of PdP

and NiP/TP)

One sees that

of the two metalloporphins

and

at 77’K the gross

are similar

similar spectra.

and should have

Figures 2 and 4 show this to be

true, in general, but PdP exhibits many more and much sharper lines.

In fact, one can see that aside

from linewidth and spectral resolution,

but that much sharper lines and greater resolution

metalloporphins

are observed in PdP.

other and suggests

As with the other metallopor-

spectra of

along with those of ZnP/TP,

ously from this laboratory (b) PdP and NIP

diagram of the st,ronger

transitions in the polarized absorption

have

all of the

gross similarities

a general description

each

of the

phins in this host [ 1, 21, there are some unpolarized

spectra of metalloporphins

lines and lines on the long wavelength

vicinity of the Q,, band, there is a strong o-polarized

side of the

in triphenylene.

to

In the

lf

W

$615 5608 5564 5.528 5429 5397 5369 5355 5286 5262 5247 $201 5172 5142 5113 5105 5077 5032 5015 4966 4921

5216,

: W 10 2 W

I;:

: 3 1

W i 2 10 LO W 3

W

I

1?1;04 17827 17968 18085 18414 18524 18620 18669 18913 18999 19053 19222 19329 19442 19552 19583 19691 19867 19935 20131 20315

77°K

r4

.

(a) PdP lines at 5436, 5323, and 4981 were not polarized.

w W W 10 W 1 4 w 1 10 8 W 1 W 3 W

5583 5522 5477 5420 5414 5373 5309 5197 5180 SO68 SOS9 SO43 5007 4991 4962 4872

17&l? 18104 18253 18445 18465 18606 18831 19237 19300 19726 19761 19824 19966 20030 20148 20520

I

P#,TP(~)

I

0

$157,

.J 5452 5346 5085 4980

5130.

I 10 1 8 5

Nip/T

5093,

18;37 18701 19661 20073

0

5025,

A 5404 5297 5227 5123 SO36

77’K 18;OO 18875 19126 19513 19851

n I 10 1 1 8 8 l&3 6&2* 15326 6523.1 6506.7* 15365 6496.0, 15390 6486.5* 15412 6472.7* 15445 6470.1 15451 15619 6400.5 6397.4* 15627 6373-l* 15687 6364.2* 15708 6359.5’ 15720 6252.6 15989 6230.9* 16045 6228. .5* 16051 6226.0’ 16057 6223.1’ 16065 6218.9* 16075 6101.3 16385 6030.0 16579 5957.4 16781 16984 5886.3 5876.3 17013 5872.1 17025 5839.3 17121 5811.9 17201 5808.8 17210 17236 5801.3 5748.1 17392 5742.3 17410 5718.7 17482 5710.8 17506 5498.6 17543 5641.0 17722 5635.8 17739 5630.6 17755 5564.3 17967 5538.6 18050

a

: 2 2 2 1 10 1 4 4 4 1 10 2 7 2 0 2 10 3 3 5 2 7 4 s 2 2 5 7 8 7 2 6 4 10 2 3 3 6191.1* 5914.6 5858.7 5797.5 5792.9 5785.2 5672.6 5668.7 5625 .O

A

16148 16903 17064 17244 17258 17’184 17624 17636 17773

n *

FBP/TP - 4.2OK

Table 1. Energy levels and relative intensities of PdP, Nil?, and FBP in triphenylene

I 8 8 2 3 4 5 8 3 3 tx * * 6057.3 5930.7 5887.7 5867.8 5832; S 5825.1 5816.0 5778 t 5 5776.3 5765.0 57S9.9 5753.6 5?39:6 5735.9 5731.3 5730.7 5690.4 5683.0 5664.0 5657.0 5652.5 5647.7 5644.5 5620.0

6446.2* 6422.6* 6407.?* 6384.3* 6378.1* 6376.7. 6315.9* 6300.9 6266.6. 6211.5*

x

l&9 15566 15602 15659 15674 15678 15829 15866 15953 16095 16180 16196 16504 16857 16980 17037 17141 17162 17189 17301 17307 17341 17357 17376 17418 17429 17443 17445 17569 17591 17650 17672 17686 17701 17711 17789

u

2” 3 4 31 4

1’0 2 10 2 2 2 4 5 4 5 5 5 S 7 3 2 2 2 2 2 2

I 44 10 10 1 1 1 10

1086

J. BOHANDY and B. F. KIM Table 2. Luminescence spoct;ra of PdP and FBP in triphenylene

PdP/TP - 4.2'K A I 6521.8 153;9** 10 7 6529.9 15310 9 6532.0 15305 3 6535.0 15298 3 6537.1 15293 1 6540.8 15284 6545.6 15273 8 4 6550.3 15262 3 6552.3 15258 6562.1 15235 5 6566.8' 15224 2 6571.9 15212 1 6638.0 15061 1 6695.3 14932** 1 6703.5 14914 2 6717.8 14882 2 6734.8 14844 1 6858.8 14576 1 6863.1 14567 2 6883.4 14524** 1 6892.9 14504 1 W 6908.2 14472 7143.3 13995** 2 7153.1 13976 5 1 7156.7 13969 7159.7 13963 1. 7169.5 13944 4 7189.1 13906 1 7195.6 13894 1 7284.7 13724** 2 7294.2 13706 5 7298.0 13699 1 7304.5 13686 1 4 7310.7 13675 7331.0 13637 1 7337.7 13625 1

PdP/TP - 77°K h I 6542 15;82 10 6720 14877 2 6886 .I4518 3 7024 14233 1 7174 13935 5 7303 13689 6 7531 13275 W 7708 12970 W

FBP/TP - 4.2'K x I 16;96 6504.3 16181 ; 6506.3* 16148 7' 6515.0 16095 10 6520.5 16076 4 6523.2* 2 6553.9* 16063 16057 1 6582.8 16051 3 6606.3 16049 2 6650.8 16044 6 6662.6 16040 3 6679.6 15953 5 6697.8 15829 6704.2 5 15813 2 6709.5 15720 8 6722.1 15709 4 6723.7 15687 6757.8 2 15678 1 6776.2 ',15675 1 6800.5 15659 3 6805.9 15627 3 6834.4 15608 3 6852.2 15602 10 6858.0 15566 4 6876.3 15534 5 6878.3 15528 3 6885.8 15508 8 6902.8 15488 2 6907 .O 15481 3 6912.0 15476 3 6915.4 15458 2 6921.0 15452 1 6946.6 15445 7 7031.4 15438 7 7058.1 15411 5 7085.9 15390 8 7146.2 7157.6

x 6172.5* 6178.2* 6191.1* 6211.4* 6218.7' 6223.7* 6225.9* 6228.S* 6229.2 6231.1* 6232.5 6266.6* 6315.8* 6322.3 6359.4* 6363.9* 6373.0* 6376.4* 6377.9* 6384.4* 6397.2* 6405.2 6407.8* 6!22.6* 6435.6 6438.2 6446.4* 6454.6 6457.7 6459.7 6467.2 6470.0* 6472.6* 6475.9 6486.9* 6496.1*

15v370 15368 15345 15332 15326 15254 15187 15133 15032 15005 14967 14926 14912 14900 14872 14869 14807 14753 14701 14689 14628 14590 14578 14538 14535 14519 14483 14474 14464 14456 14445 14391 14218 14164 14109 13989 13967

I 4 3 2 2 2 8 2 3 2 2 2 2 2 2 3 2 2 3 3 2 2 4 3 3 3 4 6 2 4 ? 2 2 2 2 2 4 3 _

*Seen in absorption and fluorescence. **Leading line of a repeating quintet. See text. line,

denotedby Q,",and & strong rr-polarized line,

et al. [ll]

who report a 30 cm-l

denoted by Q,,“, with a separation QOy-QoG on the On the basis of arguments order of 200 cm-l.

PdP in m-octane.

given in [2], this energy difference between QO’ and

1300 cm-l

Qo2 is interpreted as a crystal field reduction of the

further to the blue.

usual DJh metalloporphyrin

strong

symmetry

the subsequent removal of degeneracy. for Q,,*-Q,” is approximately 79 cm-1

for

respectively.

ZnP,

CUP,

Support

to D,, with The value

300,210,180,163 VOP,

NiP

and

for this interpretation

and PdP, has

0

spectrum

One

has

doublet

can

for

a

strong

line

approximately

Q,,’ and a weaker line 400 cm-l

from

approximately

separation

In the spectral region of QI, the

The r spectrum consists of a

whose

separations

from

1000 and 1350 cm-l,

easily

see that

these

coalesce into the structureless

Qoy are

respectively.

features

woulcl

Q0 and Q1 bands

usually observed in unpolarized room temperature

who report a

solution spectra.

Indeed,

109 cm-1 separation between Qoy and Q,,” for ZnP

phinltriphenylene

dissolved in solution yield such

in n-octane crystals and very recently by CANTERS

spectra.

been given by CANTERS et al. [lo]

crystals

of metallopor-

However, one sees evidence that the metal

1087

Optical spectra of Ni porphin, Pd porphin and free baso porphin

;-.

,.“,

,.,

.~(%

_,

,,

model: ‘It was hoped that further experimental

formation O-O

band of PdP/TP

4.2’K,

multiplets

earlier.

in-

on this point could be obtained but the at 77“K was not split and at

were

observed

as

The lack of phosphorescence

is consistent with experimental

[5] and theoretical

[12] work on nickel porphyrins. planation

discussed in NiP/TP

The tentative

[12] for the lack of luminescence

ex-

in Ni

porphyrins was the existence of low energy excited states of d-d character lying between the lowest 3(a, r*) state and the ground state. A point worthy of FBP/TP

of discussion in the spectrum

is the observation of 28 lines at identical

wavelengths

in absorption

and fluorescence.

Al-

though many of these lines appear to the red of the region of band

I, there are 9 such lines in the

vicinity of band I from 6172.5 A to 6231.1 A. of these lines are strong transitions. reasonable

assumption

that

Five

Under

fluorescence

the

occurs

from the lowest excited electronic state [13], this

NIP

means that these lines arise from pure electronic transitions.

If these multiple electronic transitions

originate from one site, this is not consistent with presently accepted porphyrin theory [14], in which band Fig. 4. A “stiok” diagram of the stronger absorption lines of some metalloporphins in triphenylene at 77°K.

I contains

Although

only

one electronic

transition.

there is evidence that multiple sites do

occur in these samples, giving multiple transitions,

can have a substantial effect on the high resolution

a large number of nonequivalent

sites.

spectra of metalloporphyrins

tiple

the

studied.

ZnP

(Although

and PdP

which have now been

have the sharpest

photographic

lines.

recording of spectra pre-

site

question

selective excitation It

electronic

it seems unlikely that there are such must

await

experiments

has been pointed

out

The mul-

outcome

of

now in progress.

[I51 that

chlorin

is a

clude accurate measurements of spectral width and

common impurity in porphin and fluoresces to the

intensity,

red of band I of porphin.

visual estimates indicate that ZnP, PdP

and FBP

have comparable

widths.)

Linewidths

It is possible that many

of the lines in the vicinity

of band I are due to

of VOP are somewhat less sharp but the resolution

chlorin and other impurities.

is still high.

LUTZ [7] made a study of band IV of FBP by reson-

CUP and NIP have broad lines with

very little detail other than the general polarized

ance Raman

features mentioned above.

band

The

vibrational

phosphorescence

frequencies spectrum

observed

of PdP/TP

general, with quasiline spectra of PdP

in

the

agree, [4].

in

The

main difference is that they report that the 9-O transition

was a singlet

multiplets PdP/TP

elsewhere. was

a

at 6388 A with complex The

O-O

multiplet.

GOUTERX~AN [5] reported

transition

EASTWOOD

that the O-O

in and

and as the temperature to 161°K

was increased from 97°K

the higher energy peak increased at the

expense of the lower one. explanation

in terms

They gave a tentative

of a “2

geometry

model”

and state that studies at lower temperatures

and

higher resolution would be necessary to verify the

spectra.

contains

transitions

They

gave

PLUS and

evidence

that

at least three pure electronic

as witnessed

by

the

observation

of

three maxima in the excitation spectra of 21 resonance Raman

bands of FBP.

pointed out the possibility in band IV.

Theory

[ 161 has also

of an electronic origin

Similar resonance Raman

spectra in

the spectral region of band I would be helpful in interpreting the results reported here.

band of

the triplet luminescence of PdP in nonane is split

IV

Reoently

It is interesting

to speculate

on the relatively

large number of unpolarized lines which were observed in these studies, especially in FBP/TP ZnP/TP. of

Electron

VOP/TP

metalloporphin substitutional

[17]

have

enters sites.

and

spin resonance measurements demonstrated the

triphenylene

that

the

host

in

There are four molecules

in

the unit cell and the normals to the triphenylene

1088

J. BOH~WDY and B. F. KIM

planes make an angle of 51’ graphic c-axis [S].

Thus,

with the crystallo-

there are four porphin

planes tilted 39’ from the c-axis and symmetrically located around the c-axis. Simple geometrical

arguments

of the polarizs-

tion characteristics of such sites, discussed in Ref. [2] predict the in-plane pletely

o-polarized,

z transitions

the in-plane

to be oom-

y transitions

to

have 3 times greater intensity in rr than in 0, and any out-of-plane intensity

ratio

techniques

z transitions of

4 :3.

to have a rr to ts

Photographic

detection

may not be able to discern this differ-

ence and it seems possible that these unpolarized lines might

be out-of-plane

be possible with photoelectric ments

to determine

sufficient origin

accuracy

could

be

transitions.

It may

intensity

measure-

the polarization to

due

conclude to

ratios with

whether

z-polarized

their

transitions.

Current theories predict no out-of-plane transitions. (It should be mentioned that the unpolarized lines could be due to transitions

to states which &se

from a mixing of levels with different polarizations.) The morphology

and size of our crystals preclude

the right geometry

to verify this for certain.

A

different host with a more favorable orientation of the porphin molecules would be a better approach REFERENCES [1] B. F. KIM, J. BOHANDY, and C. K. JEN, J. Cbem. Phys. 59,213 (1973).

[2] J. BORANDY, B. F. KIM, and C. K. JEN, J. Mo2. Spectroscopy 49, 366 (1974). [3] A. N. SEVCHENKO,K. N. SOLOV’EV, S. F. SHKIBYAN, and M. V. SARZHEVSKAYA, Dok. Akad. Nauk. l&3,1391 (1963). [4] A. T. GRADYUSEKO, V. A. UASHENKOV, and K. N. SOLOV’EV,Biofizilca 14,827 (1969). [5] D. EASTWOOD and M. GOUTERMAN, J. Mol. Spectroscopy 35, 350 (1970). [6] J. B. CALL&, G. GO~TE~AN, Y. M. JONES, and B. H. HENDERSON,J. Mol. Spectroscopy 89, 410 (1971). [7] R. PLUS and M. LUTZ, Spectroscopy Lett. 7, 73 (1974). [S] A. K~no, Acta Cry&. 8, 166 (1950). [9] B. F. KIM, J. BOHANDY, and C. K. JEN, Spectrochim. Acta 3OA, 2031 (1974). [lo] G. W. CANTERS,J. VAN EOMOND,T. J. SOHAAFSMA, and J. H. VAN DER WAALS, Molec. Phys. 24, 1203 (1972). [Ill G. W. CANTERS,M. NOORT, and J. H. VAN DER WAALS, Chem. Phys. Lett. 30, 1 (1976). [12] R. L. AKE and M. GOUTERMAN,Theoret. Chim. Acta 17, 408 (1970). [13] See, for example, M. GOUTERMAN,Emited St&en of Matter (C. W. SHOPPEE,Ed.) Graduafe Studies Texas Technioel University 2, 63-100 (1973). [14] M. GOUTER~, J. Mol. Spectroscopy 6, 138 (1961). [15] M. GOUTERMAN,Private communication. [16] A. J. MCHUGH, M. GOUTER~, and C. WEISS, Theoret. Chiwa. Acta (Be&n) 24,346 (1972). [ 171 J. BOHANDY, B. F. KIM, and C. K. JEN, J. Mug. Reson. 15, 420 (1974).