Monolayer and multilayer films of differently substituted metal tetraazaannulene complexes

Thin Solid Films, 243 (1994) 3 0 5 - 3 0 9

305

Monolayer and multilayer films of differently substituted metal tetraazaannulene complexes F. Bonosi, M. Romanelli and G Martini* Dipartimento di Chimica, Universitgt di Firenze, 50121 Firenze (Italy)

G. Ricciardi and F. Lelj Dipartmento di Chimica, Universitgt della Basilicata, 85100 Potenza (Italy)

Abstract

The properties of monolayers and multilayers of nickel(II) compounds with the dinaphtho derivative of the macrocycle ligand dinaphtho{b,i}5,7,12,14-tetramethyltetraaza[14]annulene with one and two hexadecanoyl chains on the water surface and onto a solid support have been studied from a thermodynamic and spectroscopic point of view and the results were compared with those from the dibenzo analogues. The molecular plane showed a tilted edge-on orientation at the air-water interface. The spreading monolayers were stable with time and their stability was almost independent of the compound used. The presence of hysteresis in the compression-expansion-compression cycles indicated an incomplete reversibility. Films prepared with the monohexadecanoyl macrocycle metal derivatives were regular and homogeneous whereas the occurrence of two alkyl chains on the ring resulted in a monolayer too viscous to be transferred. The effect of the film iodination was investigated through UV-visible and electron spin resonance spectroscopies.

1. Introduction

Recently the metal derivatives of the polyazamacrocycle [1,4,8,11] tetraaza[ 14]annulene (TAA) (1), namely

R1

X /

\N /

C

"CH R2

1, free ligand, X = benzoor naphtho-; R 1 = R a = hexadecanoyl: dhtmdbTAA and dhtmdnTAA 2, nickel(II) derivative; X = benzo-; R1 = Ra = hexadecanoyl: NidhtmdbTAA 3, nickel(II) derivative; X = naphtho; R1 = H; Ra = hexadecanoyl: NihtmdnTAA 4, nickel(II) derivative; X = naphtho; RI = R a - hexadecanoyl: NidhtmdnTAA

* A u t h o r to w h o m c o r r e s p o n d e n c e s h o u l d be sent.

0040-6090/94/$7.00 SS D I 0040-6090(93)04215-E

have been studied, as have those of other tetraaza macrocycle compounds such as porphyrin and phthalocyanine, because of their semiconducting, conducting and sensor properties [1, 2]. In particular, iodine doping gives to these compounds properties of highly conducting charge transfer salts [2-4]. Besides their similarity with some prosthetic groups of metalloproteins, they promise to be good molecular metals and environmental sensors. These compounds acquire amphiphilic properties after introduction of alkyl chains onto the TAA ring. Langmuir-Blodgett (LB) films of semiconducting copper(II) and nickel(II) derivatives of dibenzo-TAA have been fabricated and cadmium stearate has been used to improve deposition [2]. The monolayer properties at the air-water interface of the nickel compound 2 (NidhtmdbTAA) have been studied in our laboratory [5]. This compound gives stable and reproducible LB films whose order and orientation have been analyzed. In this paper we report the properties of films obtained with nickel(II) compounds of dinaphtho-TAA with either one or two C [16] chains in the macrocycle ring (3 and 4 respectively). As usual, we shall describe the features of the corresponding spreading monolayers on a water subphase in order to find the best experimental conditions for their transfer to a solid support before considering the possibility of fabricating thin films and studying their properties.

© 1994 - - Elsevier Sequoia. All rights reserved

F. Bonosi et al. / Monolayer and multilayer films o f differently substituted metal TAA complexes

306

2.40 (s, 12H, N=C-CH3); (t, 6H, -CH3).

2. Experimental details

1.30 (s, 52H,-CH2-); 0.90

2. I. Materials All chemicals necessary for the syntheses of the compounds studied in this work were reagent grade and were used without further purification, unless otherwise stated. The TAA metal compounds free from the alkyl chains, NitmdbTAA and NitmdnTAA respectively, were synthesized according to the procedure of Goeldken and Weiss [6]. NidhtmdmTAA (2) was prepared from NitmdbTAA by a modification of the procedure described by Eilmes [7] by reaction with freshly distilled hexadecanoyl chloride in the presence of (C2Hs)3N in refluxing toluene for 24 h at 120-130 °C. Further details of this synthesis and the sample characterization have been reported in ref. 5. The same procedure was used for the preparation of NihtmdnTAA (3) and of NidhtmdnTAA (4), starting from NitmdnTAA. After filtration of the precipitate and removal of the unreacted reagents, a gradient chromatography on silica gel by using an n-pentane-CH2C12 solution as an eluent gave two bands: the first was characterized as due to 3, and the second as due to a compound containing 4. Compound 3: yield 10% based on NitmdnTAA. Anal. Found: C, 74.58; H, 7.45; N, 7.50. C46H56N402Ni calc.: C, 74.69; H, 7.63; N, 7.57.~H nuclear magnetic resonance (NMR): 66.9-7.8 (m, 12H, aromatic rings); 2.72 (t, 2 H , - C H 2 - C O ) ; 2.22, 2.45 (s, 12H, N = C - C H 3 ) ; 1.30 (s, 2 6 H , - C H 2 - ) ; 0.89 (t, 3 H , - C H 3 ) ; 5.10 (1H, propanediiminate bridge) ppm. Compound 4: yield 10% based on NitmdnTAA. Anal. Found: C, 75.90; H, 8.55; N, 5.58. C62Hs6N402Ni calc.: C, 76.14; H, 8.86; N, 5.73%. ~H NMR: c~ = 6 . 9 8.0 (m, 12H, aromatic rings); 2.72 (t, 4 H , - C H 2 - C O - ) ;

\

~6o: \

Z

~

" \\

---',

2.NidhtmdbTAA

-. . . . . . . 4 . N i d h ~ T n d n T A A

~ zo: f~

0

I~l

1o

,,

,,

I l l ,

ao

,,r

II

I ' ' l l

50

It'

' ' l l l l l S i l '

~o

' ' l l l

I '

90

'

'

'

'

'

'

'

Ito

SURFACE AREA (A / m o l e c u l e ) Fig. 1. Spreading isotherms at 293 K of chloroform solutions of N i d h t m d b T A A (2) ( ), N i h t m d n T A A (3) ( ) and N i d h t m d n T A A (4) ( . . . . . ) on a twice-distilled water subphase.

2.2. Methods Chloroform (Merck; purity, greater than 99%) solutions of compounds 2 - 4 were used for isotherm determination on a twice-distilled Millipore Q-purified water subphase. The spreading isotherms were obtained with a KSV LB5000 apparatus under conventional conditions. LB films were deposited on hydrophilic quartz and on quartz treated with dimethyldichlorosilane [5] in order to have a hydrophobic surface. A Perkin-Elmer Lambda 5 UV-visible spectrometer was exployed for electronic spectra. The electron spin resonance (ESR) spectra were recorded with the aid of the Bruker 200D ESR spectrometer operating in the X band.

3. Results and discussion

3.1. Monolayers Figure 1 shows the 293 K spreading (surface pressure area (~-A)) isotherms of 3 and 4 on a pure water subphase. The isotherm of 2 is also shown for comparison. The isotherms of 3 and 4 were characterized by a marked slope change at surface pressures of 25 mN m and 15 mN m ~, corresponding to limiting area per molecule of 67 ~2 and 73 ~2 respectively. The C~ compressibility coefficients were lower for 3 than for 4, the highest values being 100 mN m -~ and 135 mN m ~. This result agreed for a higher lateral compressibility of the monolayer given by the monohexadecanoyl compound. To ascertain whether the pressure discontinuities represented a transition between two different surface arrangements rather than a monolayer collapse, we ran relaxation measurements of the surface area as a function of time at constant ~r values below and above the discontinuity (Fig. 2). The extent of the surface area decrease (ranging from 2.2 to 7.9% after 2 h, depending on the compound and on the pressure measurement) and its concave shape indicated a relatively high film stability with time and the occurrence of surface rearrangements of the molecules [8]. This suggestion was further proved by compressionexpansion-compression cycles of the monolayers. Figure 3 reports examples of such cycles carried out on 3 and 4 at various surface pressures. Sizable hysteresis areas were observed, more apparent at 7r > 7rtra,~. The observed film compression after the expansion cycle was very similar to the first compression, although the original ~ - A trend was not completely recovered. Even if the transition between the two surface arrangements did not seem therefore completely reversible, at least on the time scale of the experiment, the above behavior

F. Bonosi et al. / Monolayer and multilayer films of differently substituted metal TAA complexes

differing for the presence of a C 1 6 alkyl chain and with those observed for N i d h t m d b T A A (48 A2 molecule-1 [5]). The expected dependence on the ring nature was thus verified. Nevertheless, as also observed for the dibenzo compound, none of the calculated limiting areas agreed for a fiat orientation of the metal macrocycles at the a i r - w a t e r interface, which required a minimum surface area of 200-280 A 2 molecule -].

dnTAA 0.97 \ - -

~" o . 9 2 "--'<~ ~

- -

3

2

4.NidhtmdnTAA

3.2. Thin films Transfer of N i h t m d n T A A (3) onto the support treated with dimethyldichlorosilane was reliable even at rc values below the surface pressure discontinuity with high transfer ratios for both downstrokes and upstrokes (in the range 0.95-0.84, for a dipping rate of 2 m m m i n - ] ) . More than 20 layers were transferred in these conditions. Reliable monolayer transfer of N i d h t m d n T A A (4) onto the same support was only possible at ~ values above the surface pressure discontinuity. The transfer ratio decreased from 0.94 for the first deposited layer to a very low value (0.12). Details on the film properties and on the molecular arrangement were analyzed by optical spectroscopy.

\

0.97,

\ - -

0.92

.........

- -

25

~.........

0

I00

200

TIME (rain) Fig. 2. Time stability of the monolayers formed with 3 and 4 at the air-water interface. A(t) and A(0) represent the area per molecule at time t and 0 respectively.

was typical of two molecular arrangements at the surface, with different orientations of the molecules at the a i r - w a t e r interface. The following values of the limiting area per molecule were calculated from the isotherms shown in Fig. 1: N i h t m d n T A A (3) < 25 m N m -~ rc > 30 m N m -]

A(0) = 67/~2 molecule -l A(0) = 5 4 ~ k 2 molecule -]

N i d h t m d n T A A (4) rt < 15 m N m -] rc > 25 m N m -]

A(0) = 73 A~ molecule -I A(0) = 66 A2 molecule-]

3.3. Electronic spectra The electronic spectra were recorded in the range 200-800 nm under isotropic light and in the range 350-800 nm under polarized light. The spectra of 3 and 4 in CHC13 solution were the same (Fig. 4) and showed the same band features of the electronic spectra of T A A compounds [9, 10] and of 2, in particular, [5], with a significantly higher resolution. All transitions observed in 3 and 4 were red shifted with respect to 2 because of the higher delocalization in the n a p h t h o - T A A than in the benzo-TAA. Table 1 reports the frequencies of the relevant transitions.

The above values were in line with the small differences in the areas occupied by molecular structures

3.N @t trrtdTtTA,4 ~=15 m,N/m

,.--, 2 0 .

4.N£dht-trLd~TAA ~r=25 m N / m

"'" "'e

1 "~c o.rn,10,r e n ~ o . n --ee:pps'rur,~n 2"co'n~rears4o'r~

--

Z

,

e ~ p Q ~

•.

~,,~ I o -

3.N~,h~m,d~TAA ~r=32 m N / m

4oi

• • **• °

%% •

r~

r~

r~

.,¢ 4 0 r~.

4.N ~ , h kvr~d~ TA.A ~r= t 0 m, t V / m

°,

1%o~,l~'els.i~n

20

"o ,°%

\ 0

40

307

60

DO

t OO

SURFACE AREA ( A ~ / m o l e c u l e )

i ii

30

ii

illl

ii

50

i [i

ii

El

ii

70

i i,i1~1[i],,1

r

90

SURFACE AREA (.~Z/molecule)

Fig. 3. Pressure area plots during compression-expansion compression cycles of monolayers of 3 and 4.

308

F. Bonosi et al. / Monolayer and multilayer films of differently substituted metal TAA complexes

I

-- NidhtmdnT/~ (CHCIs5.9 mMsolution) - - NihtmdnTAA (LBfilm, fl layers)

,,

lllllllllllllllttlll

200

soo

I'lllllllll/lllllltlltttl

400

500

r

600

wavelength (nm)

"%b'

Dipping direction

Fig. 5. Sketch of the relationships between the incidence angle of the polarized light and the geometry of the LB film: n, normal to the substrate; k, light propagation direction; E~ and Ep, electric field vectors perpendicular and parallel to the incident plane.

Fig. 4. Electronic spectra of NidhtmdnTAA in chloroform solution (5.9 mmoll 1) and of NihtmdnTAA LB films (eight layers). TABLE 1. Optical data of nickel(I1) compounds of benzotetraaza[14]annulene and naphthotetraaza[14]annulene Compound

2m,x Et (nm) (cm i) ....

Transition

NihtmdnTAA (3) (CHC13 solution) 410 NidhtmdnTAA (4) (CHC13 solution) 464 607

24400 Soret 21550 Q,, Q(1 0) 16500 Q~, Q(0-0)

413 467 617

24200 Soret 21400 Q~, Q(I 0) 16200 Q~, Q(0 0)

NidhtmdbTAA (2) (CHCI3 solution) 394 430 589

25400 Soret 23250 Q~, Q(I o) 16980 Q,, Q(0 0)

395 440 600

25300 Soret 22730 Q~, Q(I o) 16670 Q~, O(O-0)

NihtmdnTAA (3) (8-layer LB film)

NidhtmdbTAA (2) (LB monolayer)

moment s relative to the Soret band (413 nm; y polarized) and to the Q bands (467 and 617 nm; x polarized). The reference x, y, z system was associated with the quartz slide (Fig. 5). The calculation procedure reported by Vandevyver et al. [11] was used. Without entering into the details of this calculation, from measurements by using plane-polarized light at incidence angle i = 30 °, 45 ° and 60 °, the angle ¢p between the y molecular axis and the normal to the support slide (Fig. 5) was found to be 65 ° . All the above data and their comparison with the data reported [5] for N i d h t m d b T A A (2) suggest that a compromise must be sought in the choice of the nature and number of substituents in the T A A ring to form homogeneous and reproducible LB films. A thorough analysis of the spreading monolayer may indeed give information on the possibility of LB fabrication. 3.4. Iodine treatment

The spectrum of the LB film of compound 4 under isotropic light was broader than that of the solution; only the peak at about 230 nm was clearly resolved, with a shoulder at about 280 nm. Both these bands occurred as well-resolved absorptions in solution too. The spectrum resolution did not improve with increase in the overlapped layers. The broadening of the visible peaks agrees for the high surface viscosity that led to high molecular aggregation after deposition. This high surface viscosity also prevented a homogeneous deposition of more than one layer. Better resolution of the spectrum was observed with LB films fabricated with 3, with a further red shift of the absorption maxima. In contrast with LB films of 2 [5], no perfect linearity of the absorbance with the number of virtual layers was observed. Electronic spectra with plane-polarized light were carried out for an LB film of 3 to obtain the orientation of the molecular plane from the transition dipole

Partial oxidation of metal complexes of polyaza macrocycle compounds, with halogens, particularly iodine, is used to prepare compounds with molecular conductor properties [1, 12-14]. This is currently done either with I2 vapors or with K I 3 water solution, when solid samples or fluid solutions respectively are treated. We carried out the iodine treatment of the LB films described in this work by overnight soaking in aqueous KI3 solutions at a concentration ranging from 10 -4 to 0.1 m o l l 1. The films were highly sensitive also to the lowest I3- concentration used. Figure 6 shows the UV-visible spectrum of a 16-layer film of 2 kept overnight in a K I 3 solution (5 x 1 0 - 4 m o l l - l ) . Two additional peaks appeared at 298 nm (33 550 c m - I ) and 3 6 3 n m (27 500 cm-1), owing to the iodine-metal charge transfer transition. The intensity of the transitions increased almost linearly with increasing iodine concentration. With the dinaphtho derivatives 3 and 4, almost the same results are obtained.

F. Bonosi et al. / Monolayer and multilayer films of differently substituted metal TAA complexes

NihtmdnTAA LB f i l m (24 l a y e r s ) ~<'i . • "..

- --.....

b e f o r e KIs i m m e r s i o n a f t e r KIa i m m e r s i o n difference spectrum

309

Both electronic a n d E P R spectra e n c o u r a g e the continu a t i o n o f the investigation o f the electronic p r o p e r t i e s o f 2 - 4 as solid a n d thin film phases.

Acknowledgments • \ ", •

",

T h a n k s are due to the I t a l i a n M i n i s t e r o della U n i v e r sit~ e della R i c e r c a Scientifica e T e c n o l o g i c a a n d to the Consiglio N a z i o n a l e delle Ricerche for financial help.

o II11

200

111111

I I I I I l [ l l [ l l l l l l l l l l l l ,

300

400

wavelength

500

111 1 1 1 1 1 1 1

600

Ill

,lllllll

700

References

(nm)

Fig. 6. Electronic spectra of a 16-layer film of 2 before ( ) and after ( - - -) overnight iodine treatment and their difference ( ........... ). N o E P R spectra were r e c o r d e d with t r e a t e d LB films ( u p to 60 layers), i n d e p e n d e n t l y o f the iodine concent r a t i o n used. R i n g o x i d a t i o n is r e p o r t e d to occur in i o d i n e - t r e a t e d T A A , with the f o r m a t i o n o f a m a c r o cycle c a t i o n r a d i c a l t h a t gives a single n a r r o w E P R line centered at g ~ 2 . 0 2 - 2 . 0 4 [12]. Similar a l t h o u g h larger signals have been r e p o r t e d for i o d i n e - o x i d i z e d t e t r a b e n z o p o r p h y n a t o n i c k e l ( I I ) [15]. A single n a r r o w ( A B = 0 . 5 - 0 . 6 m T ) a b s o r p t i o n centered at g = 2.027 was also o b s e r v e d in o u r n i c k e l ( I I ) - T A A c o m p o u n d s t r e a t e d with I2 in the p o w d e r state. U n f o r t u n a t e l y the fine features o f this w e a k signal c o u l d n o t be a n a l y z e d in greater detail since they were m a s k e d b y a s t r u c t u r e d signal o w i n g to a c o p p e r ( I I ) i m p u r i t y which i n v a r i a b l y occurred as a result o f the p r e p a r a t i o n p r o c e d u r e . H o w ever, the o b s e r v a t i o n o f the g = 2 . 0 2 7 signal was e n o u g h to assess a p a r t i a l ring o x i d a t i o n . This a b s o r p tion was n o t o b s e r v e d in the LB films simply because o f its very low intensity due to the small a m o u n t o f a b s o r b i n g m a t e r i a l in the r e s o n a n t cavity. Signals att r i b u t a b l e to N i ( I I I ) were n o t o b s e r v e d in solid c o m p o u n d n o r in LB films after I2 t r e a t m e n t . N i ( I I I ) signals are expected to be a n i s o t r o p i c with g± >gll [16, 17].

1 B. Tieke and A. Wegman, Thin Solid Films, 179 (1989) 109. 2 A. Wegrnan, M. Hunzinger and B. Tieke, J. Chem. Soc., Chem Commun., (1989) 1174• 3 M. Hunzinger, B. Hilti and G• Rihs, Heir. Chim. Acta, 64 (1984) 82. 4 L.-S. Liu, T. J. Marks, C. P. Kannewurf, J. W. Lyding, M. S. McClure and T.-C. Wang, J. Chem. Soc., Chem. Commun., (1980) 954. 5 F. Bonosi, F. Lely, G. P. Ricciardi, M. Romanelli and G. Martini, Langmuir, 9 (1993) 268. 6 V. L. Goedken and M. C. Weiss, Inorg. Synth., 20(1980) 115. 7 J. Eilmes, Polyhedron, 4 (1985) 943. 8 B. P. Binks, Adv. ColloM Interface Sci., 34 (1991) 343. 9 C. L. Bailey, R. D. Bereman, D. P. Rillema and R. Nowak, Inorg. Chem., 23 (1984) 3956. 10 A. Rosa, G. Ricciardi, F. Lelj and Y. Chizhov, Chem. Phys•, 161 (1992) 127. 11 M. Vandevyver, A. Barraud, A. Ruaudel-Teixier, P. Maillard and C. Gianotti, J. Colloid Interface Sci., 85 (1992) 571. 12 J.-J. Andr6, M. Bernard, C. Piechocki and J. Simon, J. Phys. Chem., 90 (1986) 1327• 13 M. D. Pace, W. R. Barger and A. W. Snow, Langmuir, 5(1989) 973. 14 F. Lelj, G. Morelli, G. Ricciardi, M. Romanelli and M. F. Ottaviani, Polyhedron, 10 (1991) 1911. 15 J. Martinsen, L. J. Pace, T. E. Phillips, B. H. Hoffmann and J. A. Ibers, J. Am. Chem• Sot., 104 (1982) 83. 16 C. N. Sethulakshmi, S. Subramainan, M. A. Bennett and P. T. Manoharan, Inorg. Chem., 18 (1979) 2520. 17 F. V. Lovecchio, E. S. Gore and D. H. Busch, J. Am. Chem. Sot., 96 (1974) 3109.