Visible spectra of dicarbonyl substituted tris-bipyridyl ruthenium(II) complexes

Volume 76, number

VISIBLE

1

SPECTRA

TRWBIPYRIDYL

CHEMICAL

OF DICARBONYL RUTHENIUM(II)

PHYSICS

15 November

LETTERS

SUBSTITUTED

COMPLEXES

Wtlham E. FORD and Melvm CALVIN Loboratory

1980

Berheie_1,

of Cherrucal Btodynonzrcs, Lawrence Berhefej Laboratory, Catrfomln 94 7-30. LK4

Recewcd

18 July 1980

Llmretwt~

of Calrfonrra,

The solLent dependence of the metal-to-hgand charge-transfer band pattern of tns-blpyrldyl ruthemum(I1) derwxtwes \rqth carbonyl substltuents 1s attnbuted to a reduction m the energy requued for electron transfer to the dxarbonylated blp> ndyl hgand wth an mcrease m solvent poktnty

dialkyl carboxyhc acid ester deof the tns(2.2’-blpyridyl)rutheruum(II) complex (abbrewated to [Ru(blpy)3 I”+), whch were first The mrxed-hgand

nvatwes

prepared and characterized by Spnntschmk et al. [ I], have a marked solvent dependence of their optlcal absorption and ermssion spectra parent complex. The &ketone

[2-S] compared to the analogue prepared by

Johansen et al. [8] etibtts stmiiar solvent-dependent spectra [8 J, as does the drcarboxrmide denvatrre prepared by us (fig. 1) [9]. The three mixed-lrgand malogues wll be abbrevtated as [(btpy),Ru(btpyCOR)J’+ (R = -0C,8H37. -C,8H37, or -NHC,6H33).

where the two carbonyl substttuents are located m the para (4.1’) poslfions of one of the blpyridlne h_ads_

Transfer of [(brpy )ZRu(btpy-COR)]‘+ from an aqueous solvent to an orgamc solvent causes the vtstble metal-to-ligand charge-transfer absorption band wth two maxtma to collapse mto a band wtth a single peak, and the enusslon ma_umum blue-stufts ‘Ibe long-

chanted ruthentum complexes are promtstng as electron-transfer photosensrtrzers m solar energyconvertmg devrces [l-13], so It IS important to understand the effect of solvent on then electromc structure, as reflected by therr spectra. Johansen et al. [8] consrdered the possrbrhty that the absorption spectra mdicored

changes

in the state

of aggregatton

of the rir-

carbonylated compleues. In tlus letter we suggest that the solventdependence of the spectra of [(brpy)2Ru(bipy-COR)J’+ anscs from stabtlizatton of the charge-transfer exctted state relatrve to the ground state by increasmg solvent pohutty. Spectral changes assocrated with transfer of [(bipy), Ru(bipy-COR)] ?+ from aqueous to organic solventcbear a stnhng resemblance to the changes assocrated wrth deprotonatron of the carboxyhc acid

[(blpy)ERu(blpy-CONHC,6H~3)]2+ Fig. 1. Structural

formulaof

[(b1py)2Ru(b~pyCONHC16H33)]~-

substttuents of [(btpy)z Ru(bipy-COOH)] 2c [2,3,7_14j. The absorption and ermssion spectra of [Cbipy),Ru(bipy-COHNC, 6H33)] z+ dluolved In chloroform and in aqueous detergent soluuon, which represent the extreme cases that we have observed for this complex, are reproduced in fig. 2. (Four absorption bands have 105

Volume

76. number 1

CHEMICAL

PHYSICS LETTERS

loo

15 November

1980

-

80 Ill

60 40

[lompy$Rti(blpy-CONH+,l+] n aqueous d&w@

(Cl C&l2 _ sohon

x20/3

-;“-:yiL

20 3 0

;

IIZ

I

II 250

3bO

350

I 4aO

450

500

550

6OOX/nm

350

400

450

500

550

60CXhm

(-) and emtssron (---) spectra of [(b~py)zRu(~I~YCONHC~~H~~)](CIO~)~ Hz0 luolred III chloroform

FIN. 2 Absorpuon

and III aqueous detergent rolutlon. The detergent (0 010 h¶) IS CH~(CH~)ISN+(CH$CH~CH~CH~SO~ The emw.lon spectra are uncorrected

been labelled I to IV for sake of dlscusslon.) For companson, the absorption spectra of the protonated and lomzed forms of [(blpy), Ru(blpy-COOH)] 2* m aqueous solution are shown in fig. 3. The correspondence between the changes in absorption spectral patterns of the two complexes m&cates that the perturbations of the electronic strucmres of the complexes were simdar III both cases and ;mpkates a role of the carbony1 substltuents. JYhe absorption spectrum of [(bipy),Ru(blpym other solvents had charactenstics coNH+$-f33)]2+ mtermehate to the two extremes of fig. 3,. A plot of the frequency of the long-wavelength peak of band I (tima,) versus the dielectric constant of the solvent, as a measure of solvent polarity, indicated that aqueous solvents were exceptional. However, the plot of gmax versus the mdebrand solubdity parameter [l.S],wh~ch is currently the most lvldely applied index of solvent 106

3 Absorption spectra of the toruzed and protonated forms of [(brpy),Ru(brpyCOOH)](PF& dissolved III squeous I 0 M KC1 solution Upper trace pH = 5 81. Lower traceph’ = 1 05 @H adjusted wath concentrated HCI). Rg

polanty [ 151, was roughly linear, mcluding points corresponding to aqueous media (fig. 4). There was a poor correlation between fir&x and either Kosower’s [ 161 Z- or Relchardt’s [ 171 ET-values. Unfortunately, no single parameter can be used to charactenze solvent polanty [ 17 1. Nevertheless, the results tndicate that the effect of solvent on the spectrum of [(bipy)zRu(bipyCOmC16 HS3)] *+ was mainly one of polarsty, with no specific solvent-complex mteractions (e.g. hydrogen bond&g) being obvious.

Volume

CHEMICAL

76, number 1

PHYSICS

15 November

LETTERS

1980

[(blpy)? Ru(brpy-COOH)]2t and by [(bipy)? Ru(bipy-

FIN. 1 Plot of the peak frequency of the vwble charge transfer band (I) of [(blpy)zRu(blpyCONHCt6HJx)] (ClO& - Hz0 rersus the Htldebrand solubtbty parameter of the solvent. Points a to e correspond to the cornpIe\ dspersed m the followmg aqueous media: a, water. b, 0.10 M ammonium acetate, c. the chlonde form of the complex tn aster d, phosphattdylchohne vcs~clcs, e, m detergent solution The hne was obtamed usmg least-squares analysis mcludmg all pomts except a to e

The

decrease

m d,,,

w-zth Increasu2g

solvent

polnr-

CONHC,6H33)]2+ (figs. Z and 3), the effect of increasing solvent polanty on the spectrum of the latter can be attnbuted to making more favorable chargetransfer configuratrons \ath the promoted electron on one of the carbonyl oxygen atoms, which have greater &pole moments than do configurations wrth the electron on one of the pyridyl rings. The changes m absorption bands II and III that accompany changes m band I in figs. 2 and 3 support involvement of the carbonyl substituents. Band Ii has been assigned to the transItIon involvmg electron transfer from Ru(II) (d orbltal) to the second lowest rr* orbital of bipy [ 181. Both charge-transfer bands I and 11 red-shift by ~1 kK, supportmg that assignment. Band III IS the composite of the mam intraligand (rr,~*) transitions [ 18.23,23] The shculder near 305 nm ts due to the bipy-CONHC,,H,, hgand, and the increased prommence of the shoulder that accompanies the red-shtfts of bands I and II further lmphcates a role of the carbonyl substltuents rn the spectral changes shown m figs. 2 and 3. We therefore contend that the solvent dependeme obszrved

by us [9]

zmd others

[Z-8]

of the vislbk

rty lmphes that the lowest photoexclted state of [(blpy)zRu(bipy-CONHC16H33)]2+ has a greater

and ultravrolet absorptron spectra of dicarbonyl substrtuted derrvatrves of [Ru(bipy)3]z+ arises mainly

&pole moment than does the ground state of the complex [ 171, wluch 1s consistent wivlth the metal-tohgand (d,, rr*) charge-transfer assignment for the VISable absorption bands of [Ru(bipy)3]2+ and related complexes [ 18-211. The charge-transfer configuratron of [Ru(bipy)s I 2+ is wewed as havmg a Ru3+ core coordmated to a bipyridme amon ra&cal [20]. The optnzally transferred electron in photoexctted [(bipy)22+ can presumably reside on Ru(bipy-CONHC16H33)] either the blpy or bipy-CONHC,6H33 hgands. In the

from stablllzatlon of the (d,, a*(brpy-COR)) transiuons relative to the (d,, rr*(bipy)) transition. The changes m the \lslble absorption band patterns can to some extent be accounted for by assuming that the charge transfer absorption bands are. approximately, composites of bands due to m&vidual Ru(II)-ligand mteractions [4,24]. Thus, the spectral pattern of [Ru(blpy)g I ‘+ is relatively msensltive to solvent because the three (d,, A*) transttions are equally affected. A practical consequence of the soltent dependence of the spectrum of [(blpy)ZRu(blpy-CONHC16H33)]1C is that the polarity of the enwronment of the chromo-

latter

case,

resonance

forms

can be drawn

in

which

the electron ISon the oxygen atom of one of the arrude subsntuents. Therefore the dipole moment of the (d,, n*(bipy-CONHC16H33)) excited state IS greater than that of the (d,, n*(blpy)) state, the Ifference dependmg on the relative contribution of carbonyl-locahzed electron configurations. In the case of [(btpy)2Ru(btpy-COOH)]2+, deprotonauon of the carboxylic acid would be expected to disfavor locahzation of the optically promoted electron on the carbony1 oxygen atoms 141. In view of the similanties m the two extreme absorption patterns exiblted by

phore can be assessed from the shape of the spectrum.

The absorption spectrum of this complex kolved m phosphatidylcholme bdayer vesicle dispersions [ lo,12 J resembles the spectrum of the complex in other aqueous media (points labelled a to e in fig. 4), so we infer that the dye molecules are onented in the vesicles Ike the phosphohpid molecules, wtth their charged chromophores located near the bilayer-water interface.

107

CHEMICAL

Volume 76, number 1

TIus work was supported

PHYSICS

by the Division of Chem-

ical Sciences, Office of Basic Energy Sciences, U S Department

[9] W E. Ford, Ph D. Thesis, Umverslty of Cabfornia, Berkeley (1980) [ 101 W E. Ford, J-W. Otvos and hf Calvm, Nature 274 (1978) 507. [I

11

of Energy. [ 111 [ I3 j

References

[14] [I 1 G. Spnntschntk. H.W. Sprmtschmk, P P. Kusch and D G. HiIutren, J. Am. Chem Sot. 98 (1976) 2337. [2] S-l. Valcnty and G.L. Cannes Jr , J Am. Chem. Sot 99 (1977) 1285. j3I G. Sprmtschmk. H-W. Sprmtschruk, P P Kusch and D.G. Whltten. J. Am Chem Sot 99 (1977) 4947. 141 K--P. Seefeld, D. hfdbms and H. Kuhn, Web. Chum Acta

60 (1977) 2608 151 A. Harriman.. J Chem. Sot. Chem Commun. (19773 777. i6j

L-Y.

YcUowiees.

R G. Dzckerson.

C S Haflxda>. 3 S.

Bonham and L E Lyons, Australian J. Chem 31 (1978) 431. f7] G.L Gzmes Ji- , P E. Behnken and SJ. Valentl*, J Am. Chem Sot. 100 (1978) 6549 [S J 0. Johansen, C. Rowala, A W.-H hlau and W H F. Sassc, AusrraImn 1. Chem 33 (1979) 1453.

[IS] [16] [li’] [ 181

[19] [ 201 [21 j

Y. Tsutsm. K Takuma, T. NIS~IJIIM and T Matsuo. Chem Letters (1979) 617 W E. Ford, J.W. 0~x1s and M. Calvin, Proc. Nat1 Acid. Sa. US 76 (1979) 3590. 0. Jofxmsen, C. Kowafa, A W -H hfau and W F H. Sasse, Austrahan 3. Chem. 32 (1979) 2395. P J Glordano, C.R. Bock, hI S. Wqhton, L V. Interrante and R F X Wdhatns, J. Am Chem. Sot 99 (1977) 3187 L Snyder, Chemtech (1979) 750. E.i%f. Kosower, J. Am. Chem. Sot 80 (1958) 3253 C. Relchardt, Angeu. Chem. Intern Ed.4 (1965) 29. G hf. Bryant, J E. Ferguson and H KJ Poweli. Australian J Chem. 11 (I 971) 257. G A. Gosby. Accounts Cbem Res- 8 (1975) 1-3l_ N Sutm and C Creutz, Advan. Chem. Ser. I68 (I 978) I _ F. Fetru, J. Ferguson,

H f~. Giidel and A. Ludr, Chem.

Phys. Letters 62 (1979) 153. [22] A-J. McCaffery, S-F. Mason and B J. Norman, 5. Chem. Sot. A (1969) 1428 [23] S.F. Mason and B J Norman, J. Chem Sot. A (1969) 1442. f%] S. Anderson, K R Seddon and R D Wright, Chem Phys

108

15 November 1980

LETTERS

Letters 7 1 (1980)

220