A Tightly Coupled Linear Array of Perylene, Bis(Porphyrin), and Phthalocyanine Units that Functions as a Photoinduced Energy-Transfer Cascade

6634

J . Org. Chem. 2000, 65, 6634-6649

A Tigh tly Cou p led Lin ea r Ar r a y of P er ylen e, Bis(P or p h yr in ), a n d

P h th a locya n in e Un its th a t F u n ction s a s a P h otoin d u ced

En er gy-Tr a n sfer Ca sca d e

Mark A. Miller,^†Robin K. Lammi,^‡Sreedharan Prathapan,^†,§Dewey Holten,*^,‡,†and

J onathan S. Lindsey*^,†

Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, and

Department of Chemistry, Washington University, St. Louis, Missouri 63130-4889

jlindsey@ncsu.edu

Received May 23, 2000

We have prepared a linear array of chromophores consisting of a perylene input unit, a bis(free

base porphyrin) transmission unit, and a free base phthalocyanine output unit for studies in artificial

photosynthesis and molecular photonics. The synthesis involved four stages: (1) a rational synthesis

of trans-AB₂C-porphyrin building blocks each bearing one meso-unsubstituted position, (2) oxidative,

meso,meso coupling of the zinc porphyrin monomers to afford a bis(zinc porphyrin) bearing one

phthalonitrile group and one iodophenyl group, (3) preparation of a bis(porphyrin)-phthalocyanine

array via a mixed cyclization involving the bis(free base porphyrin) and 4-tert-butylphthalonitrile,

and (4) Pd-mediated coupling of an ethynylperylene to afford a perylene-bis(porphyrin)-

phthalocyanine linear array. The perylene-bis(porphyrin)-phthalocyanine array absorbs strongly

across the visible spectrum. Excitation at 490 nm, where the perylene absorbs preferentially, results

in fluorescence almost exclusively from the phthalocyanine (Φ_f) 0.78). The excited phthalocyanine

forms with time constants of 2 ps (90%) and 13 ps (10%). The observed time constants resemble

those of corresponding phenylethyne-linked dyads, including a perylene-porphyrin (e0.5 ps) and

a porphyrin-phthalocyanine (1.1 ps (70%) and 8 ps (30%)). The perylene-bis(porphyrin)-

phthalocyanine architecture exhibits efficient light-harvesting properties and rapid funneling of

energy in a cascade from perylene to bis(porphyrin) to phthalocyanine.

In tr od u ction

output units at opposite ends of the linear array enables

detection of the flow of energy from one end of the

assembly to the other. In the case of 1 or 2, preferential

excitation of the boron-dipyrrin dye input unit results in

emission almost exclusively from the free base porphy-

rin output unit.

We sought to refine the design of 1 and 2 by incorpo-

rating different pigments with characteristics that would

extend the range of possible applications and by employ-

ing linkers that provide stronger electronic coupling

among the pigments and thus faster rates of photoin-

duced energy transfer. The design we chose (3) is shown

in Chart 1. The changes to the composition of array 3

relative to 1 and 2 are as follows:

(1) For the input unit, a perylene unit is employed in

place of the boron-dipyrrin dye. The well studied perylene

dye, perylene-3,4,9,10-bis(dicarboximide), exhibits strong

absorption in the spectral region between the porphyrin

Soret and Q bands (ꢀ_{490 nm}∼50,000 M^-1cm^-1),⁸near-unity

fluorescence quantum yield,⁹a long and monophasic

fluorescence lifetime (∼3.8 ns),¹⁰and very high photo-

stability.⁹Perylene-porphyrin¹¹and perylene-phthalo-

cyanine¹²dyads that incorporate perylene-bis(imides)

One of our objectives is to construct multipigment

arrays that strongly absorb visible light and funnel the

resulting excited-state energy rapidly and efficiently to

a designated site.^1-4Such arrays can serve as light-

harvesting elements in artificial photosynthetic systems

or as wires in molecular photonic devices. One means of

directing the flow of energy toward the final energy

acceptor involves the use of a systematic energy cascade

along a sequential array of pigments.⁵We have con-

structed two examples of such a system (1⁶and 2⁷) that

incorporate a boron-dipyrrin dye (input), one or three

zinc porphyrins (transmission unit), and a free base

porphyrin (output) (Chart 1). The positioning of input and

* To whom correspondence should be addressed. (D.H.) E-mail:

holten@wuchem.wustl.edu.

^†North Carolina State University.

^‡Washington University.

^§Permanent Address: Department of Applied Chemistry, Cochin

University of Science and Technology, Cochin, India 682022.

(1) Li, J .; Lindsey, J . S. J . Org. Chem. 1999, 64, 9101-9108.

(2) Li, F.; Yang, S. I.; Ciringh, Y.; Seth, J .; Martin, C. H., III; Singh,

D. L.; Kim, D.; Birge, R. R.; Bocian, D. F.; Holten, D.; Lindsey, J . S. J .

Am. Chem. Soc. 1998, 120, 10001-10017.

(3) Li, F.; Gentemann, S.; Kalsbeck, W. A.; Seth, J .; Lindsey, J . S.;

Holten, D.; Bocian, D. F. J . Mater. Chem. 1997, 7, 1245-1262.

(4) Hsiao, J .-S.; Krueger, B. P.; Wagner, R. W.; J ohnson, T. E.;

Delaney, J . K.; Mauzerall, D. C.; Fleming, G. R.; Lindsey, J . S.; Bocian,

D. F.; Donohoe, R. J . J . Am. Chem. Soc. 1996, 118, 11181-11193.

(5) Van Patten, P. G.; Shreve, A. P.; Lindsey, J . S.; Donohoe, R. J .

J . Phys. Chem. B 1998, 102, 4209-4216.

(8) Demmig, S.; Langhals, H. Chem. Ber. 1988, 121, 225-230.

(9) (a) Rademacher A.; Ma¨rkle, S.; Langhals, H. Chem. Ber. 1982,

115, 2927-2934. (b) Ebeid, E. M.; El-Daly, S. A.; Langhals, H. J . Phys.

Chem. 1988, 92, 4565-4568.

(10) Ford, W. E.; Kamat, P. V. J . Phys. Chem. 1987, 91, 6373-6380.

(11) O’Neil, M. P.; Niemczyk, M. P.; Svec, W. A.; Gosztola, D.;

Gaines, G. L., III; Wasielewski, M. R. Science 1992, 257, 63-65.

(12) Liu, S.-G.; Liu, Y.-Q.; Xu, Y.; J iang, X.-Z.; Zhu, D.-B. Tetrahe-

dron Lett. 1998, 39, 4271-4274.

(6) Wagner, R. W.; Lindsey, J . S. J . Am. Chem. Soc. 1994, 116,

9759-9760.

(7) Manuscripts in preparation.

Published on Web 09/02/2000

Photoinduced Energy-Transfer Cascades

J . Org. Chem., Vol. 65, No. 20, 2000 6635

Ch a r t 1

have been reported. Perylene-monoimide dyes also have

been prepared and exhibit attractive absorption fea-

tures,¹³though much less is known about their excited-

state properties. Based on considerations of the effects

of orbital ordering on electronic communication and

electron-density distributions,¹⁴we chose a perylene

monoimide dye rather than a bis(imide) dye for use as

the input unit (vide infra). We have recently found that

excited-state energy transfer from a perylene monoimide

to a free base porphyrin via an ethynylphenyl linker (4)

is extremely fast (e0.5 ps).⁷

transfer from porphyrin to the phthalocyanine. A variety

of free base and metalated porphyrin-phthalocyanine

combinations were examined. A dyad comprised of a free

base porphyrin and a free base phthalocyanine (5) gave

a high yield (>98%) of energy transfer without noticeable

photochemical side reactions.

Furthermore, the excited-state energy characteristics

are such that downhill energy flow from a porphyrin to

a phthalocyanine can be achieved independent of the

metalation states of the units, providing advantages in

the design, synthesis, and utility of the devices.^1,15,16In

particular, free base porphyrins can be used as energy-

transfer donors or transmission elements with free base

phthalocyanines as acceptors; in contrast, when zinc

porphyrins and free base porphyrins are used exclusively

in arrays, the latter must serve as the energy-transfer

acceptor.

(3) For the transmission unit, we sought to incorporate

a meso,meso-linked porphyrin dimer. Osuka and co-

workers have pioneered the synthesis of all-meso-linked

multiporphyrin arrays comprised of up to 128 por-

phyrins.^17-23To our knowledge, energy-transfer studies

(2) For the output unit, a free base phthalocyanine is

employed in place of the free base porphyrin. Phthalo-

cyanines absorb very strongly in the red and can emit

with a very high fluorescence quantum yield (0.7-0.8).

We recently studied the energy-transfer properties of

phenylethynyl-linked porphyrin-phthalocyanine dyads¹⁵

(and star-shaped pentads)¹⁶and observed strong absorp-

tion in the blue and red as well as rapid (e10 ps) energy

(13) Feiler, L.; Langhals, H.; Polborn, K. Liebigs. Ann. 1995, 1229-

1244.

(14) (a) Strachan, J . P.; Gentemann, S.; Seth, J .; Kalsbeck, W. A.;

Lindsey, J . S.; Holten, D.; Bocian, D. F. J . Am. Chem. Soc. 1997, 119,

11191-11201. (b) Yang, S. I.; Seth, J .; Balasubramanian, T.; Kim, D.;

Lindsey, J . S.; Holten, D.; Bocian, D. F. J . Am. Chem. Soc. 1999, 121,

4008-4018.

(15) Yang, S. I.; Li, J .; Cho, H. S.; Kim, D.; Bocian, D. F.; Holten,

D.; Lindsey, J . S. J . Mater. Chem. 2000, 10, 283-296.

(16) Li, J .; Diers, J . R.; Seth, J .; Yang, S. I.; Bocian, D. F.; Holten,

D.; Lindsey, J . S. J . Org. Chem. 1999, 64, 9090-9100.

(17) Osuka, A.; Shimidzu, H. Angew. Chem., Int. Ed. Engl. 1997,

36, 135-137.

(18) Yoshida, N.; Shimidzu, H.; Osuka, A. Chem. Lett. 1998, 55-

56.

(19) Ogawa, T.; Nishimoto, Y.; Yoshida, N.; Ono, N.; Osuka, A.

Chem. Commun. 1998, 337-338.

6636 J . Org. Chem., Vol. 65, No. 20, 2000

Miller et al.

of such meso,meso-linked arrays have not been performed

with input and output units on opposite ends of a linear

array. The combination of perylene, meso,meso-linked

porphyrins, and phthalocyanine is anticipated to absorb

strongly across the visible spectrum, enhancing the light-

harvesting capabilities of the array.

butylphenyl group was selected as one N-aryl substituent

to enhance the solubility, chemical stability, and light

fastness.^8-10,13For rapid through-bond energy transfer,

the linker should be attached at sites where the frontier

molecular orbitals of the donor and acceptor have high

electron density.¹⁴For porphyrins bearing electron-rich

groups at the meso positions, the a_2uorbital is generally

the HOMO. The a_2uorbital has considerable electron

density at the meso carbons but little density at the

â-pyrrole positions. Accordingly, such porphyrins should

be joined to the linker at the meso rather than the â-

position.¹⁴For perylenes, the orbital coefficients at the

3, 4, 9, and 10 positions are large,²⁴consistent with a

significant influence by the 3,4,9,10-substituents (and

little or no influence by the N-substituents)²⁵on the

absorption spectra. Due to the very large orbital coef-

ficient at the 9-position,²⁴substitution at this site ap-

peared particularly attractive for enabling efficient linker-

mediated electronic communication between the perylene

and the porphyrin. Accordingly, we decided to synthesize

a perylenedicarboximide derivative bearing an ethyne at

the 9-position. Bromination of the perylene mono-imide

6 as described by Feiler et al.¹³afforded 7 (Scheme 1).

Subsequent Pd-mediated coupling²⁶with trimethylsilyl-

acetylene gave the ethyne-substituted perylene dye 8,

which was deprotected using Bu₄NF on silica gel to give

the ethynyl perylene dye 9. Treatment of 9 with iodo-

benzene under Pd-coupling conditions afforded the phen-

yl-capped ethynylperylene (10) for use as a photophysical

reference compound.

The requisite porphyrin building blocks are of the

trans-AB₂C type, which can be prepared using a rational

synthesis that we recently developed.^27,28In this ap-

proach, a dipyrromethane and a dipyrromethane-di-

carbinol are reacted under mild nonscrambling conditions

to give the corresponding porphyrin. The dipyrromethanes

are produced in a one-flask synthesis, and the dipyr-

romethane-dicarbinols are obtained by diacylation of the

dipyrromethane followed by reduction. Thus, reaction of

11²⁹and 13³⁰afforded porphyrin 14 in 18% yield (Scheme

2). However, the solubility of 14 was poor despite the

presence of two 4-tert-butylphenyl groups. In an effort

to prepare more soluble porphyrin building blocks, 12²⁹

and 13 were reacted to give porphyrin 15, which bears

two 3,5-di-tert-butylphenyl groups. The solubility of 15

is high and rivals that of porphyrins bearing meso-mesityl

groups. It is noteworthy that no detectable scrambling

of the meso substituents was observed in the preparation

of porphyrins 14 and 15.

(4) For the linker joining the pigments, we employed

a phenylethyne unit in place of the diphenylethyne unit

in order to facilitate stronger interpigment electronic

coupling and more rapid rates of energy transfer.

We also sought to refine the synthetic methodology for

constructing linear arrays of pigments. The synthesis of

1 and 2 involved the repetitive use of Pd-coupling

reactions, requiring extensive chromatography at each

stage of the synthesis. In our recent synthesis of multi-

porphyrin-phthalocyanine arrays,^1,16we employed comple-

mentary chemistries in successive stages of the synthetic

plan. The latter approach avoids accumulation of similar

byproducts at each stage and affords the opportunity for

distinct purification regimens following each stage of

synthesis. The synthesis of a linear array comprised of

perylene, bis(porphyrin), and phthalocyanine units re-

quires reactions involving porphyrin formation, phtha-

locyanine formation, meso,meso-coupling, and Pd-cou-

pling methods.

In this paper, we present the synthesis of a linear array

of perylene, meso,meso-linked porphyrin dimer, and

phthalocyanine chromophores (3). Examination of the

static absorption and fluorescence spectra in toluene

reveal strong absorption across the visible spectrum and

efficient funneling of energy from perylene to phthalo-

cyanine. The photodynamics of energy transfer have been

investigated by time-resolved absorption spectroscopy.

Resu lts

Syn th esis Ap p r oa ch . We sought to prepare a sequen-

tial array containing perylene, meso,meso-linked por-

phyrin dimer, and phthalocyanine chromophores in a

linear or star-shaped architecture. The strategy we

intended to utilize involved the following steps: (1) Pd-

mediated coupling of the perylene and a porphyrin

yielding a perylene-porphyrin dyad, (2) the synthesis of

a porphyrin-phthalocyanine pentad (star-shaped archi-

tecture) or dyad (linear architecture) by cyclization of a

porphyrin-phthalonitrile, and (3) the oxidative meso,-

meso-coupling of the perylene-porphyrin dyad with the

porphyrin-phthalocyanine pentad or dyad. The investi-

gation of this route revealed unanticipated difficulties

with these various chemistries. The route that succeeded

involved oxidative coupling to give the meso,meso-linked

porphyrin dyad bearing one iodo group and one phtha-

lonitrile moiety, conversion to the phthalocyanine to give

the bis(porphyrin)-phthalocyanine, and Pd-mediated

coupling to attach the perylene unit to the functionalized

bis(porphyrin) to give the linear array (3).

The synthesis of porphyrin-phthalocyanine arrays

(pentads or dyads) where the porphyrin has a free meso

site is best accomplished using a trans porphyrin bearing

one phthalonitrile group and one free meso site. We

have previously prepared porphyrin-phthalocyanine

pentads by cyclization of an A₃B-type porphyrin bearing

P r ep a r a tion of Bu ild in g Block s. The synthesis of

a perylene dye building block employs chemistry estab-

lished by Langhals and co-workers. The 2,5-di-tert-

(24) Adachi, M.; Murata, Y.; Nakamura, S. J . Phys. Chem. 1995,

99, 14240-14246.

(25) Langhals, H.; Demmig, S.; Huber, H. Spectrochim. Acta 1988,

44A, 1189-1193.

(26) Ames, D. E.; Bull, D.; Takundwa, C. Synthesis 1981, 364-365.

(27) Cho, W. S.; Kim, H. J .; Littler, B. J .; Miller, M. A.; Lee, C. H.;

Lindsey, J . S. J . Org. Chem. 1999, 64, 7890-7901.

(28) Rao, P. D.; Dhanalekshmi, S.; Littler, B. J .; Lindsey, J . S. J .

Org. Chem., in press.

(29) Clausen, C.; Gryko, D. T.; Dabke, R. B.; Dontha, N.; Bocian, D.

F.; Kuhr, W. G.; Lindsey, J . S. J . Org. Chem., in press.

(30) Littler, B. J .; Miller, M. A.; Hung, C. H.; Wagner, R. W.; O’Shea,

D. F.; Boyle, P. D.; Lindsey, J . S. J . Org. Chem. 1999, 64, 1391-1396.

(20) Nakano, A.; Osuka, A.; Yamazaki, I.; Yamazaki, T.; Nishimura,

Y. Angew. Chem., Int. Ed. Engl. 1998, 37, 3023-3027.

(21) Ogawa, T.; Nishimoto, Y.; Yoshida, N.; Ono, N.; Osuka, A.

Angew. Chem., Int. Ed. Engl. 1999, 38, 176-179.

(22) Yoshida, N.; Aratani, N.; Osuka, A. Chem. Commun. 2000, 3,

197-198.

(23) Aratani, N.; Osuka, A.; Kim, Y. H.; J eong, D. H.; Kim, D. Angew.

Chem., Int. Ed. 2000, 39, 1458-1462.

Photoinduced Energy-Transfer Cascades

J . Org. Chem., Vol. 65, No. 20, 2000 6637

Sch em e 1

Sch em e 2

meso-unsubstituted porphyrin 14 or 15 under Pd-medi-

ated conditions that are compatible with porphyrins,³²

affording the corresponding dyads 22 or 23 (Scheme 4).

Though the solubility of 14 was poor, the addition of the

perylene unit in dyad 22 greatly increased the solubility.

A perylene-porphyrin dyad of interest as a photochemi-

cal benchmark was prepared in similar manner by first

coupling the ethynylperylene dye (9) and iodo-substituted

zinc porphyrin (21) to give Zn -4 in 88% yield (Scheme

5). The zinc porphyrin 21 is conveniently obtained upon

separation of a mixture of zinc porphyrins following a

mixed-aldehyde condensation.³³Demetalation with TFA

then gave the desired reference dyad 4 containing the

free base porphyrin.

We initially sought to prepare a star-shaped array with

a phthalocyanine at the core and perylene-bis(porphyrin)

units as radial arms. In our prior syntheses of porphyrin-

phthalocyanine light-harvesting arrays from porphyrin-

phthalonitriles,^1,15,16the classical Linstead conditions³⁴

(lithium pentoxide in refluxing pentanol) afforded higher

yields than the more modern Shiraishi conditions³⁵(DBU

and a metal salt in refluxing pentanol). The cyclization

of 19 under Linstead conditions gave the characteristic

color changes of a typical phthalocyanine forming reac-

tion, but the product 24 could not be isolated, presumably

due to the insolubility of the products (Scheme 6). The

a phthalonitrile group¹⁶and porphyrin-phthalocyanine

dyads by mixed cyclization of the same porphyrin-

phthalonitrile and an alkyl-substituted phthalonitrile.¹⁵

The synthesis of a trans porphyrin bearing one phtha-

lonitrile group and one free meso site is shown in Scheme

3. Treatment of 5-[4-[2-(trimethylsilyl)ethynyl]phenyl]-

dipyrromethane (16, not shown)²⁷with K₂CO₃afforded

the unprotected ethyne 17,²⁸which was coupled with

4-iodophthalonitrile³¹to give the desired dipyrromethane

18 on a multigram scale. The reaction of 18 and 11 under

the standard conditions for dipyrromethane + dipyrro-

methane-dicarbinol coupling afforded porphyrin 19 in

23% yield. The solubility of 19 was poor, so 18 and 12

were reacted to give 20, which proved to be more sol-

uble. Again, no detectable scrambling of the meso sub-

stituents was observed in the preparation of porphyrins

19 and 20.

(31) Marcuccio, S. M.; Svirskaya, P. I.; Greenberg, S.; Lever, A. B.

P.; Leznoff, C. C. Can. J . Chem. 1985, 63, 3057-3069.

(32) Wagner, R. W.; Ciringh, Y.; Clausen, P. C.; Lindsey, J . S. Chem.

Mater. 1999, 11, 2974-2983.

(33) Lindsey, J . S.; Prathapan, S.; J ohnson, T. E.; Wagner, R. W.

Tetrahedron 1994, 50, 8941-8968.

(34) Barrett, P. A.; Frye, D. A.; Linstead, R. P. J . Chem. Soc. 1938,

1157-1163.

(35) (a) Tomoda, H.; Saito, S.; Ogawa, S.; Shiraishi, S. Chem. Lett.

1980, 1277-1280. (b) Tomoda, H.; Saito, S.; Shiraishi, S. Chem. Lett.

1983, 313-316.

Rou tes to Ar r a ys. Perylene-porphyrin dyads were

prepared by coupling an ethynylperylene dye (9) with the

6638 J . Org. Chem., Vol. 65, No. 20, 2000

Miller et al.

Sch em e 3

The products were readily separated by chromatography

on silica. The Pd-mediated coupling of Zn -26 and ethy-

nylperylene 9 afforded Zn -27 in 82% yield.

The cyclization of Zn -27 to form the phthalocyanine

at the core of a star-shaped array proved to be unsuc-

cessful. The reaction under Linstead conditions resulted

in decomposition of the perylene dye, and no product was

obtained upon use of Shiraishi conditions. Attempts to

construct a linear array by a mixed cyclization of Zn -27

and 4-tert-butylphthalonitrile under Shiraishi conditions

also failed, as did the similar reaction of Zn -26 (or free

base 26) and 4-tert-butylphthalonitrile.

We then turned to the preparation of a linear array

with the desired sequence of perylene, bis(porphyrin), and

phthalocyanine units. Treatment of free base bis(porphy-

rin) 26 and 4-tert-butylphthalonitrile under Linstead

conditions afforded the desired bis(porphyrin)-phthalo-

cyanine triad 28 in 30% yield (Scheme 8). The final

reaction in the synthesis of the linear array involved the

Pd-mediated coupling of 28 and 9, affording 3 in 58%

yield. Note that 3 exists as a number of isomers. There

are four possible regioisomers due to the position of the

tert-butyl groups at the periphery of the phthalocyanine

moiety, two isomers due to the orientation of the 2,5-di-

tert-butylphenyl group attached to the perylene dye, and

other (interconverting) isomers due to the orientation of

the N-H protons at the core of the phthalocyanine and

the two porphyrins.

To serve as a benchmark for photochemical studies,

meso,meso-linked porphyrin dimer 30 was prepared by

the route shown in Scheme 9. Oxidative meso,meso-

coupling of 29 afforded Zn -30 in 83% yield (obtained

previously from a mixed meso,meso-coupling reaction²⁹).

Demetalation of Zn -30 with TFA gave the free base 30

in 95% yield. Tetra-tert-butylphthalocyanine 31 served

as a spectroscopic reference compound for the phthalo-

cyanine unit in 3.

cyclization of 20 under the same conditions gave the

desired pentad 25 in 32% yield. The star-shaped array

25 is similar to those prepared previously except for the

lone unsubstituted meso position on each porphyrin. The

metalation of 25 with zinc acetate resulted in forma-

tion of the array comprised of four zinc porphyrins and

one free base phthalocyanine (Zn 25), as evidenced by

the characteristic absorption spectrum, emission spec-

trum (free base phthalocyanine band at 725 nm), and

intense molecule ion peak observed upon LD-MS analy-

sis. The selective metalation of a porphyrin in a por-

phyrin-phthalocyanine array has been demonstrated

previously.^15,16Treatment of Zn -25 with excess pery-

lene-porphyrin Zn -22 under oxidative coupling condi-

tions (AgPF₆, DMA, CHCl₃, room temperature) slightly

modified²⁹from those originally developed by Osuka^17,22

afforded a complex mixture of products in which incom-

plete coupling was observed and purification proved to

be difficult. This result prompted a change of strategy

that led us to develop a perylene-porphyrin-porphyrin

trimer (27), which incorporated a phthalonitrile group

for subsequent phthalocyanine formation.

Absor p tion a n d flu or escen ce sp ectr a . The absorp-

tion spectrum of 3 in toluene at room temperature is

shown in Figure 1. The linear array 3 absorbs strongly

across much of the visible region. Figure 1 also shows

spectra of reference compounds representing the subunits

of 3: the phenylethynylperylene monoimide (10), the

meso,meso-linked porphyrin dimer (30), and tetra-tert-

butylphthalocyanine (31). The spectrum of the linear

array resembles but does not match the sum of the

spectra of the component parts, due largely to the effects

of the ethynylphenyl linker on the perylene and the

phthalocyanine units.

The dramatic splitting of the porphyrin Soret bands

(∼418 and ∼455 nm) is characteristic of the meso,meso-

linked porphyrin motif,^17,20-23as is apparent for both 3

and 30; the four, weaker porphyrin visible bands extend

from Q_Y(1,0) at ∼525 nm to Q_X(0,0) at ∼660 nm. The

A route to the perylene-bis(porphyrin) triad Zn -27 is

shown in Scheme 7. Oxidative coupling of Zn -15 and

Zn -20 gave the zinc porphyrin dyad Zn -26 (45% yield),

as well as the homocoupled product of Zn -15 (30% yield)

and the homocoupled product of Zn -20 (23% yield)

(assignments of homocoupled products based on LD-MS).

Photoinduced Energy-Transfer Cascades

J . Org. Chem., Vol. 65, No. 20, 2000 6639

Sch em e 4

perylene (with the ethynylphenyl linker attached in both

3 and 10) has three resolved vibronic features: the (0,0)

band at ∼530 nm (which overlaps the porphyrin Q(1,0)

band but is 1.3-fold more intense), the (1,0) band at ∼480

nm that falls between the porphyrin Soret and Q fea-

tures, and the (2,0) band (which appears as a shoulder

on the (1,0) feature) that underlies the longer-wavelength

porphyrin Soret component. The absorption bands of the

phenylethynyl-substituted perylene in 10 or 3 lie ap-

proximately 15 or 30 nm to the red of those in the

unsubstituted perylene monoimide 6 (which has its (0,0)

band at ∼505 nm) reflecting very effective electronic

communication between the perylene and the ethy-

nylphenyl linker (and an appended porphyrin).⁷The

phthalocyanine absorption characteristics in 3 differ

slightly from those of tetra-tert-butylphthalocyanine (31).

However, similar spectral changes were evident in the

porphyrin-phthalocyanine dyad 5, which incorporates

the same ethynylphenyl linker and a phthalocyanine

substituted with six heptyl groups.¹⁵Accordingly, the

spectral differences observed in the phthalocyanine ab-

sorption bands in linear array 3 versus the phthalocya-

nine reference compound 31 cannot be attributed to

regioisomers but instead arise from electronic and sym-

metry effects due to the appended ethynylphenyl linker

in the porphyrin-phthalocyanine motif.

the bis(porphyrin) ∼40%, and the phthalocyanine only

several percent. Emission occurs almost exclusively from

the phthalocyanine moiety. The perylene emission is

decreased by at least 200-fold relative to the isolated

chromophore 10 (which has Φ_f) 0.95⁷). No discern-

ible band due to the porphyrin emission is evident

(expected at 665 nm), though any such emission would

be partially obscured by the short-wavelength shoulder

on the phthalocyanine emission spectrum. The fluores-

cence quantum yield of 3 upon illumination in the

phthalocyanine band is 0.78, to be compared with 0.77

for tetra-tert-butylphthalocyanine (31).³⁶The excitation

spectrum of 3 (λ_em) 697 nm) closely matches the

absorption spectrum from 350 to 650 nm. In summary,

the static fluorescence data are consistent with (1)

essentially quantitative energy transfer from the perylene

and the bis(porphyrin) to the phthalocyanine, and (2)

intense emission from the phthalocyanine that is undi-

minished from that of the isolated chromophore.

Tim e-R esolved Ab sor p t ion a n d F lu or escen ce

Stu d ies. The perylene-bis(porphyrin)-phthalocyanine

array 3 was excited at 529 nm, where the perylene

absorbs preferentially (perylene ∼60% of the light, bis-

(porphyrin) ∼40%, phthalocyanine only a few percent; see

Figure 1). The rate of photoinduced energy transfer from

the excited perylene to the ground-state phthalocyanine

The fluorescence spectrum of 3 in toluene at room tem-

perature upon excitation at 490 nm is shown in Figure

2. At 490 nm, the perylene absorbs ∼60% of the light,

(36) Teuchner, K.; Pfarrherr, A.; Stiel, H.; Freyer, W.; Leupold, D.

Photochem. Photobiol. 1993, 57, 465-471.

6640 J . Org. Chem., Vol. 65, No. 20, 2000

Miller et al.

Sch em e 5

component (via the intervening porphyrin dimer) was

assessed by monitoring the growth of the phthalocyanine

bleach near 700 nm (Figure 3). This feature develops very

rapidly between 0.2 and 4 ps after excitation, nearly

reaching its maximum amplitude; a small amount of

additional growth occurs between 4 and 49 ps after

excitation.³⁷Kinetic analysis of data in the 695-700 nm

region (Figure 4) shows that 90% of the excitation arrives

on the phthalocyanine with a time constant of 2.0 ( 0.1

ps; 10% arrives more slowly, in 13 ( 5 ps.

A similar experiment was performed on the bis-

(porphyrin)-phthalocyanine array 28, which lacks the

perylene unit. The bis(porphyrin) was excited at 526 nm.

The phthalocyanine bleach near 700 nm again developed

with dual-exponential kinetics, with time constants of 1.3

( 0.3 ps (70%) and 13 ( 5 ps (30%).

Lifetimes of the excited singlet states of the isolated

chromophores and of the phthalocyanine component of

the array were measured using fluorescence modulation

(phase shift) spectroscopy. The phthalocyanine unit in

array 2 has an excited-state lifetime of 6.0 ( 0.5 ns, which

is the same as that measured for tetra-tert-butylphtha-

locyanine 31 (both solutions contain dissolved oxygen).

The finding of the same phthalocyanine lifetime in the

array and the monomeric reference compound is in accord

with the essentially identical phthalocyanine fluorescence

yield in the two systems. The excited-state lifetime of the

isolated meso,meso-linked porphyrin dimer 30 of 9.7 (

0.5 ns (degassed; 8.0 ( 0.5 ns undegassed) is slightly

shorter than that of reference monomers such as free

base tetramesitylporphyrin (∼13 ns degassed; ∼10 un-

degassed).^15,38The excited-singlet-state lifetimes and

fluorescence yields of the perylene reference compounds

in toluene are as follows: 4.8 ns and 0.99 for unsubsti-

tuted perylene 6, 3.9 ns and 0.97 for ethynylperylene 9,

and 3.4 ns and 0.95 for phenylethynylperylene 10.⁷

Discu ssion

A linear array of pigments that functions as an energy

cascade can serve as a light-harvesting element in

artificial photosynthesis or as a wire in molecular pho-

tonic devices. In both applications, strong absorption and

efficient energy funneling are desirable, though the

nature of the output of the energy cascade differs. In

artificial photosynthesis, the linear array would deliver

energy to a reaction center and thus fluorescence would

not be the desired output (though a long-lived excited

singlet state of the last excited component in the array

is highly desirable). In molecular photonic devices, a very

bright fluorescence output would be attractive in a

number of applications. A bright output element is also

useful in fundamental studies of energy flow. An at-

tractive design for achieving an energy cascade involves

the sequential arrangement of pigments having a pro-

gressive increase in long-wavelength absorption band

(i.e., progressive decline in excited-state energy). The

(37) The small phthalocyanine bleach at ∼700 nm in the 0.2 ps

spectrum (about 8% of the ultimate amplitude) can be attributed to

two sources: (1) direct excitation of the phthalocyanine in a small

fraction of the arrays and (2) ultrafast energy transfer with a time

constant of ∼1 ps from the fraction of the bis(porphyrin)s that were

excited (judging from results on the porphyrin-phthalocyanine dyad

5, where similar small early-time phthalocyanine bleaching in a small

fraction of the arrays was observed).¹⁵Similarly, a small change in

the shape of the bleaching spectrum at early times similar to that seen

in Figure 2 was found for the porphyrin-phthalocyanine dyads 5 and

ascribed to energy relaxation within the phthalocyanine and other

effects.¹⁵

(38) Yang, S. I.; Seth, J .; Strachan, J . P.; Gentemann, S.; Kim, D.;

Holten, D.; Lindsey, J . S.; Bocian, D. F. J . Porphyrins Phthalocyanines

1999, 3, 117-147.

Photoinduced Energy-Transfer Cascades

J . Org. Chem., Vol. 65, No. 20, 2000 6641

Sch em e 6

synthesis of such an array must yield pigments joined

by appropriate linkers such that energy flows in a rapid

manner without deleterious photoreactions. The new

array 3 possesses these favorable characteristics.

Syn th etic Str a tegy. One approach to the synthesis

of linear arrays involves the sequential attachment of

modular building blocks in proceeding from one end to

the other. Ideally, such an approach would employ no

statistical reactions, involve minimal chromatography,

and afford the desired target molecule in a minimum

number of steps.¹In developing a route to 3, we encoun-

tered a number of limitations in synthetic methodology

that precluded a straightforward linear synthesis of the

array. Chief among these limitations are (1) the absence

of a directed route to AB-type meso,meso-linked por-

phyrin dyads and (2) the lack of a simple and rational

method for preparing A₃B-type phthalocyanine building

blocks. Furthermore, the incompatibility of the perylene

monoimide dye with phthalocyanine-forming conditions

(lithium pentoxide in refluxing pentanol) required that

the perylene not be present when the phthalocyanine is

formed.

The successful synthesis of 3 employed the following

sequence of steps: (1) rational synthesis of porphyrin

building blocks containing one unsubstituted meso site,

one functional group (iodo or phthalonitrile moiety), and

two 3,5-di-tert-butylphenyl groups for increased solubility

(15, 20); (2) a statistical reaction of two porphyrin

building blocks to form the AB-type meso,meso-linked

bis(porphyrin) bearing one iodo group and one phthalo-

cyanine moiety (26); (3) a statistical reaction of the bis-

(porphyrin) with 4-tert-butylphthalonitrile yielding the

corresponding A₃B-type phthalocyanine (28), and (4) Pd-

mediated coupling to attach the perylene (9) to the bis-

(porphyrin)-phthalocyanine unit. Though the use of

statistical reactions is unattractive, in both cases the

polarity differences of the various components were

sufficient to enable straightforward chromatographic

separation. This route provided access to the desired

linear array 3 for photochemical studies.

En er gy-Tr a n sfer Ra tes a n d Yield s. Excitation of

the perylene and bis(porphyrin) components of 3 (with

∼60/40 relative absorption at either 490 or 529 nm) re-

sults in rapid arrival of energy on the phthalocyanine

6642 J . Org. Chem., Vol. 65, No. 20, 2000

Miller et al.

Sch em e 7

component. The excitation arrives predominantly (90%)

on the phthalocyanine with a time constant of 2 ps; the

remainder (10%) arrives in 13 ps. Even the slower time

constant is over 2 orders of magnitude shorter than

the excited-state lifetimes of the isolated perylene and

bis(porphyrin) chromophores (3.4 ns for 10, 9.7 ns for

30). This simple comparison and the fact that fluores-

cence occurs almost exclusively from the phthalocyanine

regardless of which chromophore is excited are evidence

of the extremely fast and efficient funneling of energy

from perylene to bis(porphyrin) to phthalocyanine.

The measured 2-ps (major) and 13-ps (minor) time

constants reflect the excited-state decay properties of

the photoexcited perylene (PMI*) and/or bis(porphyrin)

(P₂*) members of array 3. These decay pathways in-

clude the energy-transfer processes given in eqs 1

and 2.

PMI*-P₂-Pc f PMI-P₂*-Pc

PMI-P₂*-Pc f PMI-P₂-Pc*

(1)

(2)

These two processes will occur sequentially upon direct

absorption by the perylene component, and both sequen-

tially and in parallel upon absorption of both the perylene

and bis(porphyrin) components. The latter is the case for

the 529-nm excitation wavelength used in the time-

resolved absorption experiments, which produce PMI* in

∼60% of the arrays and P₂* in ∼40%. These events make

difficult the determination of the rate constants for

Photoinduced Energy-Transfer Cascades

J . Org. Chem., Vol. 65, No. 20, 2000 6643

Sch em e 8

energy-transfer processes (1) and (2) from experiments

on the perylene-bis(porphyrin)-phthalocyanine array 3

alone. However, it can be concluded from the 2-ps

dominant lifetime component in 3 and lifetimes of 3.4

ns and 9.7 ns for reference compounds 10 and 31,

respectively,³⁹that the rate constant and yield for each

transfer step must be g (3 ps)^-1and >99%.

transfer occurs from PMI* to the porphyrin with a rate

constant of g(0.5 ps)^-1.⁷The photoexcited porphyrin in

4 in toluene has the same excited-state lifetime and

fluorescence yield as in benchmark monomeric porphy-

rins, again indicating the absence of deleterious quench-

ing processes.

Thus, the predominant 2-ps time constant for the

arrival of excitation on the phthalocyanine in the

perylene-bis(porphyrin)-phthalocyanine (3) is in line

with the rates observed in the dyads. In particular, this

value is essentially the sum of the time constants of 1.3

ps found in the bis(porphyrin)-phthalocyanine 28 (or 1.1

ps in porphyrin-phthalocyanine 5) and e0.5 ps in perylene-

porphyrin 4 (plus <1 ps for equilibration/relaxation

events within the bis(porphyrin)). It is also clear that the

13 ps minor (10%) component to the growth of excitation

on the phthalocyanine in 3 is associated with energy

To deduce the rate constants for the sequential energy-

transfer steps (1) and (2), the 2-ps (90%) and 13-ps (10%)

lifetime components found in the perylene-bis(porphy-

rin)-phthalocyanine array 3 can be compared with the

values found in the subunits and reference compounds.

Following excitation of the bis(porphyrin) in the iodo-bis-

(porphyrin)-phthalocyanine compound 28, P₂* decays

and the excited phthalocyanine Pc* forms by energy-

transfer process (2) in two parts: a major component with

a time constant of 1.3 ps (70%) and a minor component

with a time constant of 13 ps (30%). Similar results were

found for the porphyrin-phthalocyanine dyad 5, in which

the excited porphyrin shows a dual-exponential decay

with time constants of 1.1 ps (70%) and 8 ps (30%).^15,16

The fluorescence yield and lifetime of the phthalocyanine

in 5 are essentially the same as those of the isolated

chromophore, indicating the absence of deleterious quench-

ing processes. In perylene-porphyrin dyad 4, energy

(39) The rate constant for each step is derived using the formula

k_trans) 1/τ_DA- 1/τ_Dwhere 1/τ_DA) k_rad+ k_isc+ k_ic+ k_transand 1/τ_D

k_rad+ k_isc+ k_ic. The yield is determined using the formula Φ_trans

)

k_trans‚ τ_DA) 1 - τ_DA/τ_D. These equations assume that no processes

other than energy transfer, fluorescence, internal conversion, and

intersystem crossing contribute to the decay properties of PMI* and

P₂* in 3. This assumption is valid for 3, based on our work on perylene-

porphyrin dyads⁷and porphyrin-phthalocyanine dyads and pen-

tads.^15,16

6644 J . Org. Chem., Vol. 65, No. 20, 2000

Miller et al.

Sch em e 9

F igu r e 1. Ground-state absorption spectra in toluene at room

temperature of the linear array 3 and reference compounds;

the latter are scaled appropriately in intensity to best match

the spectrum of 3.

F igu r e 2. Fluorescence spectrum of linear array 3 in toluene

at room temperature (λ_ex490 nm).

(porphyrin)-phthalocyanine array 3 exhibits many fa-

vorable light-harvesting and energy-funneling charac-

teristics, including the following: (1) good spectral cover-

age across the blue and red regions, (2) ultrafast and

essentially quantitative energy transfer from the perylene

end to the phthalocyanine end of the array, and (3)

emission from the phthalocyanine acceptor that is as

bright and long-lived as in the isolated chromophore. The

properties of 3 are particularly favorable relative to the

original wires (1 and 2) that contained a boron-dipyrrin

input dye, one or three zinc porphyrin transmission

transfer from the bis(porphyrin) to the phthalocyanine,

as such a component is also found in dyads 28 and 5,¹⁵

which lack the perylene subunit. The origin of this minor

component is not known but is a feature of all phenyl-

ethyne-linked porphyrin-phthalocyanine arrays that we

have examined.^15,16The ultrafast energy-transfer dynam-

ics in this tightly coupled system stem from the nature

of the input and output chromophores, the phenylethyne

linkers, and the strong electronic interactions within the

bis(porphyrin) transmission unit.^23,40

Com p a r ison of Lin ea r Ar r a y (3) w ith th e F ir st-

Gen er a tion Ar r a ys (1) a n d (2). The perylene-bis-

(40) Bhuiyan, A. A.; Seth, J .; Yoshida, N.; Osuka, A.; Bocian, D. F.

J . Phys. Chem. in press.

Photoinduced Energy-Transfer Cascades

J . Org. Chem., Vol. 65, No. 20, 2000 6645

F igu r e 3. Time-resolved absorption difference spectra of

linear array 3 in toluene at room temperature at several times

after excitation with a 130-fs flash at 529 nm.

F igu r e 4. Kinetic data and dual-exponential fit for linear

array 3 in toluene showing ∆A averaged over the 695-700

nm region as a function of time after excitation (see Figure

3). The phthalocyanine bleaching develops (as excitation

arrives via energy transfer from the bis(porphyrin) unit) with

time constants of 2 ps (90%) and 13 ps (10%). The inset shows

an expanded view of the data at early times. The data before

t ) 0 and during the flash are omitted for clarity.

elements, a free base porphyrin output unit, and diphen-

ylethyne linkers. The advantages of 3 compared to the

components and linkers employed in 1 and 2 can be seen

from the following considerations.

In a boron-dipyrrin-porphyrin dyad (32), which rep-

resents the input section of 1 and 2, energy transfer

occurs from the excited boron-dipyrrin dye to the free

base porphyrin in dual-exponential fashion with rate

constants of (2.9 ps)^-1(36%) and (24 ps)^-1(64%) (due to

two excited-state conformers of the dye).²By comparison,

there is a second, minor component to the excited-state

dynamics associated with the porphyrin-phenylethyne-

phthalocyanine motif that has a time constant of ∼10

ps.¹⁵The phthalocyanine absorbs strongly in the red and

has a lower-energy excited state than the porphyrin

transmission element irrespective of the metalation

states of these components, permitting use of free base

porphyrins as energy-transfer donors. The free base

phthalocyanine in 3 emits with the same high efficiency

(Φ_f) 0.78) and lifetime (6 ns) as in the isolated chro-

mophore, indicating the absence of charge-transfer or

other quenching processes involving the bis(porphyrin)

unit. In contrast, the emission efficiency of the free base

porphyrin in 1 is 0.12.⁶Thus, there are many advantages

of using a porphyrin-phenylethyne-phthalocyanine out-

put section relative to a diphenylethyne-linked zinc

porphyrin and free base porphyrin as in the original wires

1 and 2.

While our studies of end-to-end photoinduced energy

transfer in 1 and 2 are still in progress, the results in

hand indicate that the overall transfer process in 3 is

approximately 5-10 times faster than the single-step

transfer process in a diphenylethyne-linked boron-dipyr-

rin-porphyrin dyad (32) or zinc porphyrin-free base

porphyrin dyad (33). Thus, phenylethyne-linked perylene

and phthalocyanine components appear ideal as input

and output units for use in porphyrin-based energy-

transfer systems. The meso,meso-linked transmission

unit affords rapid energy transfer. In summary, we have

constructed and characterized a perylene-bis(porphy-

rin)-phthalocyanine array that has superior light-

harvesting and energy-funneling properties compared to

our first-generation wires (1 and 2), including long-

distance ultrafast energy-transfer dynamics.

energy transfer in 3 proceeds with a rate that is fast

(g(3 ps)^-1) and single exponential. The perylene also has

modestly strong absorption in the blue-green region that

complements the extended coverage in the blue region

afforded by the bis(porphyrin) linker (due to the split

Soret bands) and by the phthalocyanine in the red.

In a diphenylethyne-linked zinc porphyrin-free base

porphyrin dyad (33), which represents the output section

of 1 and 2, energy transfer occurs with a rate constant

of (24 ps)^{-1 4}

.

By comparison, the rate of energy transfer from por-

phyrin to phthalocyanine with a phenylethyne linker is

much faster (1.1 ps porphyrin lifetime for the dominant

process). One drawback of the phthalocyanine is that

Exp er im en ta l Section

1

Gen er a l Meth od s. H NMR spectra were collected at 300

MHz in CDCl₃unless otherwise stated. All absorption and

6646 J . Org. Chem., Vol. 65, No. 20, 2000

Miller et al.

emission spectra were collected in toluene. Mass spectra of

porphyrins and porphyrin-containing compounds were ob-

tained via laser desorption mass spectrometry (LD-MS) in the

absence of an added matrix.⁴¹A full presentation of the LD-

MS spectra of the arrays is available in the Supporting

Information. High-resolution fast atom bombardment mass

spectrometry (FAB-MS) studies of the compounds were carried

out at greater than unit resolution unless stated otherwise.

All chemicals were used as received from Aldrich. The por-

phyrins prepared by rational synthesis were examined for

scrambling by LD-MS analysis of crude reaction mixtures.⁴²

Solven ts. All solvents were dried by standard methods.

Toluene (Fisher, certified ACS) and triethylamine (Fluka,

puriss) were distilled from CaH₂, and tetrahydrofuran (Fisher,

histological grade) was distilled from Na/benzophenone. Tet-

rahydrofuran (Fisher, HPLC grade) and all other solvents were

used as received.

Ch r om a togr a p h y. Adsorption column chromatography

was performed using flash silica gel (Baker, 60-200 mesh) or

alumina (Fisher A-540, 80-200 mesh). Preparative-scale size

exclusion chromatography (SEC) was performed using BioRad

Bio-beads SX-1.⁴³A preparative scale glass column was packed

using Bio-Beads SX-1 in tetrahydrofuran and eluted with

gravity flow. Following purification, the SEC column was

washed with 2 volume equiv of solvents used.

dissolved oxygen or were deoxygenated by bubbling with N₂

as indicated.

Tim e-Resolved Absor p tion Sp ectr oscop y. Transient

absorption data were obtained at room temperature as dis-

cussed elsewhere.¹⁶Samples (∼0.1 to 0.2 mM in toluene) were

placed in a 5-mm path length cuvette and stirred with a

magnetic stir bar. Samples were excited at 10 Hz with 130 fs,

25-30 µJ pump pulses and probed with white light pulses of

comparable duration. Each spectrum was acquired at a specific

pump-probe delay time using 2D-detection and represents the

average of data from 300 laser pulses. Kinetic data were

generated by averaging the ∆A values in specific wavelength

ranges (e.g., 695-700 nm) for the entire set of pump-probe

delay times and plotting these values as a function of time. A

nonlinear least-squares algorithm was used to fit the kinetic

traces to functions consisting of either a single or double

exponential plus a constant.

P er ylen e-Bis(p or p h yr in )-P h th a locya n in e (3). Follow-

ing a general Pd-coupling procedure,³²

a mixture of 28

(0.016 g, 6.8 µmol), ethynylperylene 9 (0.004 g, 6.8 µmol), Pd₂-

(dba)₃(0.005 g, 5 µmol), and P(o-tol)₃(0.011 g, 36 µmol) in

toluene/triethylamine (14 mL, 5:1) was reacted in a Schlenk

flask at 35 °C for 2 h. The crude reaction mixture was

evaporated to dryness, chromatographed (silica, toluene),

chromatographed (SEC, THF), and chromatographed (silica,

toluene/ethyl acetate, 10:1) to afford a black solid (0.011 g, 58%

yield): ¹H NMR (500 MHz) δ -2.10 to -1.90 (m, 4H), -1.50

(br s, 2H), 0.70-2.00 (m, 117H), 6.30-9.60 (m, 60H); LD-MS

obsd 2771.1; FAB-MS (unit resolution) obsd 2759.4, calcd exact

mass 2758.5 (C₁₉₂H₁₈₃N₁₇O₂); λ_abs(log ꢀ) 418 (5.26), 457 (5.28),

530 (4.98), 606 (4.54), 674 (5.00), 696 (4.99) nm; λ_em700, 714,

780 nm.

Gen er a l P r oced u r e for P d -Cou p lin g Rea ction s. Two

methods for Pd-mediated coupling were employed. For the

coupling of nonporphyrinic species where copper could be

employed, the method of Ames was used (Pd(PPh₃)₂Cl₂

+

CuI).²⁶For porphyrins, a copper-free Pd-coupling method was

employed (Pd₂(dba)₃, P(o-tol)₃).³²The iodo and ethynyl sub-

strates and the Pd reagents were placed in a Schlenk flask,

which was evacuated and purged with argon three times. The

argon flow rate was increased, the threaded stopcock was

removed, and deaerated distilled toluene and triethylamine

were added in succession by gastight syringe. The threaded

stopcock was replaced, the argon flow rate was reduced and

the Schlenk flask was immersed in an oil bath held at a

constant temperature. When the reaction was finished the

flask was cooled to room temperature and the solvents were

removed under reduced pressure. To remove Pd species the

mixture generally was filtered through a short silica column.

P h ysica l Meth od s. (1) Gen er a l. Static fluorescence and

static and time-resolved absorption studies were performed

on samples in toluene at room temperature.

P er ylen e-Eth yn ylp h en yl-Zin c P or p h yr in (Zn -4). Fol-

lowing a general Pd-coupling procedure,³²a mixture of 9 (0.016

g, 0.033 mmol), zinc(II)-5,10,15-trimesityl-20-(4-iodophenyl)-

porphyrin (21)³³(0.028 g, 0.032 mmol), Pd₂(dba)₃(4.3 mg, 4.4

µmol), and P(o-tol)₃(0.011 g, 0.036 mmol) in toluene/triethy-

lamine (13 mL, 5:1) was reacted in a Schlenk flask at 35 °C

for 1 h. The crude reaction mixture was filtered through Celite,

rotary evaporated to dryness, chromatographed on silica (CH₂-

Cl₂/hexanes, 3:1), chromatographed (SEC, THF), and recrys-

tallized (ethanol) to afford a purple solid (0.042 g, 88%): R_f

1

(silica, CH₂Cl₂/hexanes) ) 0.27; H NMR δ 1.31 (s, 9H), 1.34

(s, 9H), 1.85 (s, 18H), 2.64 (s, 9H), 7.05 (m, 2H), 7.28 (s, 6H),

7.47 (m, 1H), 7.61 (m, 1H), 7.86 (m, 2H), 8.06 (m, 4H), 8.31

(m, 2H), 8.57 (m, 2H), 8.60 (m, 2H), 8.75 (m, 8 H), 8.91 (m,

2H); LD-MS obsd 1339.1; FAB-MS obsd 1333.52, calcd exact

mass 1333.52, (C₉₁H₇₅N₅O₂Zn); λ_abs423, 515, 550 nm.

4. A solution of Zn -4 (30 mg, 0.02 mmol) in CH₂Cl₂(5 mL)

was treated with TFA (250 µL, 5 vol %) and the solution was

stirred for 2 h (with monitoring by fluorescence spectroscopy).

The crude reaction mixture was dissolved in CH₂Cl₂, washed

with NaHCO₃, washed with water, dried (Na₂SO₄), rotary

evaporated to dryness, chromatographed on silica (CH₂Cl₂/

hexanes, 5:1), and recrystallized (ethanol) to afford a purple

solid (18 mg, 62%): ¹H NMR δ -2.12 (s, 2H), 1.31 (s, 9H), 1.34

(s, 9H), 1.84 (s, 18H), 2.61 (s, 9H), 7.05 (d, J ) 2.1 Hz 1H),

7.24 (m, 4H), 7.44 (dd, J ) 8.7, 2.1 Hz, 1H), 7.58 (d, J ) 8.7,

1H), 7.80 (m, 2H), 7.98 (d, J ) 7.8, 1H), 8.05 (d, J ) 8.1 Hz,

2H), 8.27 (d, J ) 8.1 Hz, 2H), 8.48 (m, 5H), 8.67 (m, 9 H), 8.80

(d, J ) 5.1 Hz, 2H); LD-MS obsd 1275.2; FAB-MS obsd

1271.61, calcd exact mass 1271.61 (C₉₁H₇₇N₅O₂); λ_abs420, 515,

591, 651 nm.

(2) Sta tic Absor p tion a n d F lu or escen ce Sp ectr oscop y.

Static absorption (Cary 100) and fluorescence (Spex Fluoro-

max) measurements were performed as described previ-

ously.^15,16For the absorption measurements, a 1-nm data

interval, a scan speed of 600 nm/min, and a spectral bandwidth

of 2 nm were used. Fluorescence measurements utilized ∼2

µM samples, 5-nm band-pass in both excitation and detection

paths, and a right-angle geometry. Emission spectra were

corrected for the sensitivity of the detection system. Tetra-

tert-butylphthalocyanine served as a fluorescence standard (Φ_f

) 0.77).³⁶The solutions contained ambient concentrations of

dissolved oxygen.

Tim e-Resolved F lu or escen ce Sp ectr oscop y. Fluores-

cence lifetimes were measured using fluorescence modulation

(phase shift) methods on a Spex Tau2 spectrofluorimeter as

described previously.^15,16Modulation frequencies from 10 to

40 MHz were typically utilized for the samples studied here,

and both the fluorescence phase shift and amplitude modula-

tion were used in modeling the data. Samples (∼5 µM) were

excited in an appropriate Q band and the emission over the

entire profile isolated with appropriate colored glass filters.

The solutions either contained ambient concentrations of

N-(2,5-Di-ter t-bu tylph en yl)-9-[2-(tr im eth ylsilyl)eth yn yl]-

p er ylen e-3,4-d ica r boxim id e (8). Following a general Pd-

coupling procedure,²⁶a mixture of 7¹³(0.200 g, 0.34 mmol),

trimethylsilylacetylene (60 µL, 0.40 mmol), Pd(PPh₃)₂Cl₂(0.024

g, 0.03 mmol), and CuI (0.005 g, 0.02 mmol) in toluene/

triethylamine (60 mL, 5:1) was reacted in a Schlenk flask for

2 h at 50 °C. The crude reaction mixture was filtered through

Celite, evaporated to dryness, and chromatographed (silica,

CHCl₃/hexanes, 10:1) to afford a red solid (0.18 g, 88%): mp

>270 °C; R_f(silica, CHCl₃) ) 0.36; ¹H NMR δ 0.38 (s, 9H, Si),

1.30 (s, 9H), 1.33 (s, 9H), 7.05 (m, 1H), 7.11 (s, 1H), 7.44 (m,

4H), 7.67 (m, 5H), 8.28 (m, 1H), 8.39 (m, 2H), 8.62 (m, 2H);

(41) Fenyo, D.; Chait, B. T.; J ohnson, T. E.; Lindsey, J . S. J .

Porphyrins Phthalocyanines 1997, 1, 93-99.

(42) Littler, B. J .; Ciringh, Y.; Lindsey, J . S. J . Org. Chem. 1999,

64, 2864-2872.

(43) (a) Nishino, N.; Wagner, R. W.; Lindsey, J . S. J . Org. Chem.

1996, 61, 7534-7544. (b) Wagner, R. W.; J ohnson, T. E.; Lindsey, J .

S. J . Am. Chem. Soc. 1996, 118, 11166-11180.

Photoinduced Energy-Transfer Cascades

J . Org. Chem., Vol. 65, No. 20, 2000 6647

FAB-MS obsd 605.2779, calcd exact mass 605.2750 (C₄₁H₃₉

NO₂Si); λ_abs523, 493 nm.

-

reacted in a Schlenk flask at 50 °C for 0.5 h. The crude reaction

mixture was filtered through Celite, washed with CH₂Cl₂, and

evaporated to dryness. The crude product was chromato-

graphed (silica, (CH₂Cl₂/hexanes, 10:1) and recrystallized from

ethanol to afford light-orange crystals (4.7 g, 90% yield): mp

187 °C; ¹H NMR δ 5.50 (s, 1H), 5.89 (s, 2H), 6.10-6.23 (m,

2H), 6.65-6.80 (m, 2H), 7.24 (d, 2H, J ) 8.1 Hz), 7.49 (d, 2H,

J ) 8.1 Hz), 7.70-7.95 (m, 3H), 8.00 (br s, 2H); ¹³C NMR δ

43.99, 85.88, 107.57, 108.65, 114.22, 114.60, 115.22, 116.35,

117.64, 119.90, 128.78, 129.40, 131.64, 132.25, 133.50, 135.55,

136.01, 144.37; FAB-MS obsd 372.1375, calcd exact mass

372.1375 (C₂₅H₁₆N₄).

N-(2,5-Di-ter t-b u t ylp h en yl)-9-et h yn ylp er ylen e-3,4-d i-

ca r boxim id e (9). A mixture of 8 (0.051 g, 0.082 mmol) and

tetrabutylammonium fluoride on silica (0.120 g, 0.1-0.15

mmol) 10 mL of dry THF was stirred for 0.5 h under argon.

The reaction mixture was filtered through Celite, evaporated

to dryness, and chromatographed (silica, CHCl₃/hexanes, 10:

1) to afford a red solid (0.042 g, 94%): R_f) 0.27 (silica, CHCl₃);

¹H NMR (mixture of diastereomers) δ 1.31 (s, 9H), 1.34 (s, 9H),

3.67 (s, 1H), 7.05 (m, 1H), 7.11 (m, 1H), 7.44 (m, 4H), 7.65 (m,

4H), 7.77 (m, 1H), 8.28 (m, 1H), 8.37 (m, 4H), 8.62 (m, 2H);

FAB-MS obsd 533.2356 calcd exact mass 533.2355 (C₃₈H₃₁

NO₂); λ_abs(log ꢀ) 517, 486 (4.45) nm.

-

5,15-B is(4-t er t -b u t y lp h e n y l)-10-[4-[2-(3,4-d ic y a n o -

p h en yl)eth yn yl]p h en yl]p or p h yr in (19). Following a ratio-

nal synthesis,²⁸a mixture of 11²⁹(2.5 g, 5.4 mmol) and 18

(2.0 g, 5.4 mmol) in acetonitrile (2.1 L) was treated with TFA

(4.9 mL, 22 mmol) and the reaction mixture was stirred for

4.5 min. DDQ (4.9 g, 22 mmol) was added followed by

triethylamine (9.0 mL, 65 mmol) and the reaction mixture was

stirred for 1 h. The crude reaction mixture was purified by

the same procedure as for 14, affording purple crystals (0.99

g, 23% yield): ¹H NMR δ -3.01 (s, 2H), 1.63 (s, 18H), 7.70-

8.20 (m, 15H), 8.83 (d, 2H, J ) 4.5 Hz), 8.96 (d, 2H, J ) 4.5

Hz), 9.07 (d, 2H, J ) 4.5 Hz), 9.34 (d, 2H, J ) 5.1 Hz), 10.22

(s, 1H); LD-MS obsd 803.3; FAB-MS obsd 800.3628, calcd

exact mass 800.3627 (C₅₆H₄₄N₆); λ_abs417, 510, 585 nm; λ_em645,

711 nm.

5,15-Bis(3,5-d i-t er t -b u t ylp h e n yl)-10-[4-[2-(3,4-d icy-

a n op h en yl)eth yn yl]p h en yl]p or p h yr in (20). Following a

rational synthesis,²⁸a solution of 12²⁹(1.0 g, 1.7 mmol) and

18 (0.63 g, 1.7 mmol) in acetonitrile (660 mL) was treated with

TFA (1.5 mL, 20 mmol) and the solution was stirred for 5 min.

Then DDQ (1.5 g, 6.8 mmol) was added followed by triethyl-

amine (2.8 mL, 20 mmol), and the reaction mixture was stirred

for 1 h. The crude reaction mixture was purified by the same

procedure as for 14, affording purple crystals (0.19 g, 12%

yield): ¹H NMR δ -2.94 (s, 2H), 1.55 (s, 36H), 7.80-8.00 (m,

6H), 8.05-8.30 (m, 7H), 8.84 (d, 2H, J ) 4.5 Hz), 8.98 (d, 2H,

J ) 4.5 Hz), 9.08 (d, 2H, J ) 5.1 Hz), 9.36 (d, 2H, J ) 4.2 Hz),

10.25 (s, 1H); LD-MS obsd 914.9; FAB-MS obsd 912.4857, calcd

exact mass 912.4879 (C₆₄H₆₀N₆); λ_abs417, 510, 544, 586 nm;

λ_em645, 711 nm.

Zn (II)-5,15-Bis(3,5-d i-ter t-bu tylp h en yl)-10-[4-[2-(3,4-d i-

cya n op h en yl)eth yn yl]p h en yl]p or p h yr in (Zn -20). A solu-

tion of 20 (0.18 g, 0.20 mmol) in CHCl₃/MeOH (20 mL, 7:3)

was treated with zinc acetate (4.4 g, 20 mmol), and the reaction

mixture was stirred overnight. The crude reaction mixture was

washed with H₂O, dried (Na₂SO₄), and chromatographed

(silica, CH₂Cl₂/hexanes, 3:1), affording a purple solid (0.19 g,

96% yield): ¹H NMR δ 1.55 (s, 36H), 7.80-8.00 (m, 6H), 8.05-

8.35 (m, 7H), 8.95 (d, 2H, J ) 4.5 Hz), 9.08 (d, 2H, J ) 5.1

Hz), 9.17 (d, 2H, 4.5 Hz), 9.44 (d, 2H, J ) 4.5 Hz), 10.31 (s,

1H); LD-MS obsd 976.2; FAB-MS obsd 974.4025, calcd exact

mass 974.4014 (C₆₄H₅₈N₆Zn); λ_abs427, 557 nm; λ_em606, 650

nm.

P er ylen e-P or p h yr in Dya d (22). Following a general Pd-

coupling procedure,³²a mixture of 13 (0.069 g, 0.089 mmol),

ethynylperylene 9 (0.048 g, 0.089 mmol), Pd₂(dba)₃(0.012 g,

14 µmol), and P(o-tol)₃(0.033 g, 0.011 mmol) in toluene/

triethylamine (72 mL, 5:1) was reacted in a Schlenk flask at

35 °C for 2.5 h. The crude reaction mixture was evaporated to

dryness, chromatographed (silica, CH₂Cl₂/hexanes, 3:1), chro-

matographed by SEC (THF), and evaporated to afford a purple

solid (0.091 g, 90% yield): ¹H NMR δ -3.07 (s, 2H), 1.35 (s,

9H), 1.36 (s, 9H), 1.64 (s, 18H), 7.08 (d, 1H, J ) 2.4 Hz), 7.45-

7.52 (m, 1H), 7.55-7.65 (m, 2H), 7.75-7.87 (m, 5H), 8.08, 8.34

(AA′BB′, 2 × 2H), 8.15-8.30 (m, 6H), 8.25 (m, 4H), 8.54 (d,

1H, J ) 8.1 Hz), 8.61 (d, 2H, J ) 8.1 Hz), 8.92 (d, 2H, J ) 5.1

Hz), 9.00 (d, 2H, J ) 5.4 Hz), 9.06 (d, 2H, J ) 5.1 Hz), 9.30 (d,

2H, J ) 5.1 Hz), 10.16 (s, 1H); LD-MS obsd 1186.7; FAB-MS

obsd 1181.5612, calcd exact mass 1181.5608 (C₈₄H₇₁N₅O₂); λ_abs

416, 510 nm; λ_em646, 711 nm.

N-(2,5-Di-ter t-bu tylph en yl)-9-(ph en yleth yn yl)per ylen e-

3,4-d ica r boxim id e (10). Following a general Pd-coupling

procedure,²⁶a mixture of 9 (20.0 mg, 0.038 mmol), iodobenzene

(5 µL, 0.05 mmol), Pd(PPh₃)₂Cl₂(5 mg, 7 mmol), and CuI (5

mg, 0.02 mmol) in toluene/triethylamine (12 mL, 5:1) was

reacted in a Schlenk flask at 50 °C for 2 h. The crude reaction

mixture was filtered through Celite, evaporated to dryness,

and chromatographed (silica, CHCl₃/hexanes, 10:1) to afford

1

a red solid (0.015 g, 83%): mp >270 °C; H NMR δ 1.31 (s,

9H), 1.34 (s, 9H), 7.04 (d, J ) 2.1 Hz, 1H), 7.46 (m, 4H), 7.60

(m, 1H), 7.73 (m, 3H), 7.88 (d, J ) 8.1 Hz, 1H), 8.48 (m, 5H),

8.67 (dd, J ) 8.1, 1.5 Hz, 2H); FAB-MS obsd 609.2703, calcd

exact mass, 609.2668 (C₄₄H₃₅NO₂); λ_abs(log ꢀ) 358, 433, 501

(4.56), 531 (4.60) nm.

5,15-Bis(4-ter t-bu tylp h en yl)-10-(4-iod op h en yl)p or p h y-

r in (14). Following a rational synthesis,²⁸a solution of 11²⁹

(0.63 g, 1.3 mmol) and 5-(4-iodophenyl)dipyrromethane (13)³⁰

(0.45 g, 1.3 mmol) in acetonitrile (660 mL) was treated with

TFA (1.2 mL, 16 mmol) and stirred for 4.5 min. DDQ (1.2 g,

5.3 mmol) was added followed by triethylamine (1.2 mL, 16

mmol), and the reaction mixture was stirred for 1 h. The crude

reaction mixture was filtered through a pad of alumina (CH₂-

Cl₂), followed by a pad of silica (CH₂Cl₂), evaporated to dryness,

and washed with hot ethanol to afford purple crystals (0.18 g,

18% yield): ¹H NMR δ -3.01 (s, 2H), 1.63 (s, 18H), 7.79, 816

(AA′BB′, 2 × 2H) 7.95, 8.07 (AA′BB′, 2 × 2H), 8.83 (d, 2H, J

) 5.1 Hz), 8.96 (d, 2H, J ) 5.1 Hz), 9.06 (d, 2H, J ) 5.1 Hz),

9.33 (d, 2H, J ) 4.2 Hz), 10.22 (s, 1H); LD-MS obsd 779.6;

FAB-MS obsd 776.2369, calcd exact mass 776.2376 (C₄₆H₄₄N₄I);

λ_abs416, 510, nm.

5,15-Bis(3,5-d i-ter t-bu tylp h en yl)-10-(4-iod op h en yl)p or -

p h yr in (15). Following a rational synthesis,²⁸a solution of

12²⁹(1.0 g, 1.7 mmol) and 13³⁰(0.60 g, 1.7 mmol) in acetonitrile

(660 mL) was treated with TFA (1.5 mL, 20 mmol) and stirred

for 5 min. DDQ (1.5 g, 6.8 mmol) was added followed by

triethylamine (2.8 mL, 20 mmol) and the reaction mixture was

stirred for 1 h. The crude reaction mixture was purified by

the same procedure for 14, affording purple crystals (0.23 g,

15% yield): ¹H NMR δ -2.96 (s, 2H), 1.55 (s, 36H), 7.80-7.90

(m, 2H), 7.92-8.20 (m, 8H), 8.85 (d, 2H, J ) 4.5 Hz), 8.96 (d,

2H, J ) 5.1 Hz), 9.07 (d, 2H, J ) 4.2 Hz), 9.35 (d, 2H, J ) 5.1

Hz), 10.23 (s, 1H); LD-MS obsd 890.3; FAB-MS obsd 888.3643,

calcd exact mass 888.3628 (C₅₄H₅₇N₄I); λ_abs416, 509, 585 nm.

Zn (II)-5,15-Bis(3,5-d i-t er t -b u t ylp h e n yl)-10-(4-iod o-

p h en yl)p or p h yr in (Zn -15). A solution of 15 (0.20 g, 0.22

mmol) in CHCl₃/MeOH (25 mL, 3:2) was treated with zinc

acetate (4.8 g, 22 mmol), and the reaction mixture was stirred

overnight. The crude reaction mixture was washed with H₂O

and dried (Na₂SO₄). The crude product was then chromato-

graphed (alumina, CH₂Cl₂/hexanes, 3:1, then CH₂Cl₂) affording

a purple solid (0.20 g, 97% yield): ¹H NMR δ 1.55 (s, 36H),

7.80-7.88 (m, 2H), 7.90-8.30 (m, 8H), 8.96 (d, 2H, J ) 5.1

Hz), 9.06 (d, 2H, J ) 5.1 Hz), 9.16 (d, 2H, J ) 4.2 Hz), 9.43 (d,

2H, J ) 4.2 Hz), 10.29 (s, 1H); LD-MS obsd 952.9; FAB-MS

obsd 950.2742, calcd exact mass 950.2763 (C₅₄H₅₅N₄IZn); λ_abs

420, 546 nm.

5-[4-[2-(3,4-Dicya n op h e n yl)e t h yn yl]p h e n yl]d ip yr -

r om eth a n e (18). Following a general Pd-coupling procedure,²⁶

a mixture of 17²⁸(3.4 g, 14 mmol), 4-iodophthalonitrile^15,31(3.6

g, 14 mmol), Pd(Ph₃P)₂Cl₂(0.98 g, 0.14 mmol), and CuI (0.13

g, 0.71 mmol) in toluene/triethylamine (20 mL, 5:1) was

P er ylen e-Zin c P or p h yr in Dya d (Zn -22). A solution of

22 (0.040 g, 0.034 mmol) in CHCl₃/MeOH (12 mL, 2:1) was

treated with zinc acetate (0.74 g, 3 mmol), and the reaction

6648 J . Org. Chem., Vol. 65, No. 20, 2000

Miller et al.

mixture was stirred overnight. The crude reaction mixture was

then washed with H₂O, dried (Na₂SO₄), and chromatographed

(alumina, CH₂Cl₂, then ethyl acetate), affording a purple solid

(0.036 g, 97% yield): ¹H NMR δ 1.37 (s, 9H), 1.42 (s, 9H), 1.66

(s, 18H), 7.07 (d, 1H, J ) 2.1 Hz), 7.48-7.51 (m, 1H), 7.62-

7.69 (m, 3H), 7,75-8.70 (m, 19H), 9.03-9.13 (m, 6H), 9.28 (d,

2H, J ) 4.2 Hz), 10.05 (s, 1H); LD-MS obsd 1248.8; FAB-MS

obsd 1243.4739, calcd exact mass 1243.4743 (C₈₄H₆₉N₅O₂Zn);

λ_abs420, 543 nm; λ_em597, 642 nm.

P er ylen e-P or p h yr in Dya d (23). Following the general

Pd-coupling procedure,³²a mixture of porphyrin 15 (0.014 g,

0.022 mmol), ethynylperylene 9 (0.008 g, 0.02 mmol), Pd₂(dba)₃

(0.002 g, 2 µmol), and P(o-tol)₃(0.006 g, 20 µmol) in toluene/

triethylamine (6 mL, 5:1) was reacted in a Schlenk flask at

35 °C for 1.5 h. The crude reaction mixture was evaporated to

dryness, chromatographed (silica, CH₂Cl₂/hexanes, 4:1), chro-

matographed (SEC, THF), and evaporated to afford a purple

solid (0.018 g, 86% yield): ¹H NMR δ -3.00 (s, 2H), 1.36 (s,

9H), 1.37 (s, 9H), 1.57 (s, 36H), 7.09 (d, 1H, J ) 2.1 Hz), 7.45-

7.90 (m, 7H), 8.00-8.40 (m, 11H), 8.50-8.65 (m, 3H), 8.95 (d,

2H, J ) 4.5 Hz), 9.01 (d, 2H, J ) 5.4 Hz), 9.07 (d, 2H, J ) 4.5

Hz), 9.32 (d, 2H, J ) 4.2 Hz), 10.18 (s, 1H); LD-MS obsd 1299.8;

FAB-MS obsd 1293.68, calcd exact mass 1293.69 (C₉₂H₈₇N₅O₂);

λ_abs(log ꢀ) 417 (5.61), 510 (4.88), 642 (3.78) nm; λ_em645, 711

nm.

Sta r -Sh a p ed P or p h yr in -P h th a locya n in e P en ta d (25).

Following a standard procedure,^1,34a solution of pentanol

(2.5 mL) was treated with lithium ribbon (16 mg) and the

mixture was stirred at 90 °C until the lithium had reacted.

The reaction mixture was cooled to room temperature, and 50

mg of 20 was added; the reaction mixture was heated to 145

°C for 2 h and then cooled to room temperature. The reaction

mixture was dissolved in CH₂Cl₂, washed with MeOH/H₂O

(100 mL, 3:1), washed with H₂O, dried (Na₂SO₄), and chro-

matographed (silica, toluene/ethyl acetate, 20:1) affording a

purple-brown solid (0.016 g, 32% yield). A satisfactory ¹H NMR

spectrum was not obtained: LD-MS obsd 3670.6, calcd avg

mass 3654.8; λ_abs(log ꢀ) 419 (5.87), 510 (4.56), 546 (4.60), 689

(4.69), 721 (4.74) nm; λ_em725 nm.

Sta r -Sh a p ed Zin c P or p h yr in -P h th a locya n in e P en ta d

(Zn -25). A solution of 25 (0.081 g, 0.022 mmol) in CHCl₃/

MeOH (10 mL, 7:3) was treated with zinc acetate (1.9 g, 8.9

mmol), and the reaction mixture was stirred overnight. The

crude reaction mixture was washed with H₂O, dried (Na₂SO₄),

and chromatographed (silica, toluene), affording a green solid

(0.053 g, 77% yield). A satisfactory ¹H NMR spectrum was not

obtained: LD-MS obsd 3905.4, calcd avg mass 3908.3; λ_abs421,

544, 686, 722 nm; λ_em725 nm.

Iod o-Bis(zin c p or p h yr in )-P h th a lon itr ile (Zn -26). Fol-

lowing a slight modification²⁹of a procedure developed by

Osuka,^17,22a solution of Zn -20 (0.079 g, 0.081 mmol) and

Zn -15 (0.077 g, 0.081 mmol) in CHCl₃(50 mL) was treated

with AgPF₆(0.031 g, 0.12 mmol) and DMA (250 µL), and the

reaction mixture was stirred under argon for 1.5 h. The crude

reaction mixture was then washed with H₂O, dried (Na₂SO₄),

and evaporated to dryness. The crude product was chromato-

graphed (silica, CH₂Cl₂/hexanes, 3:1) yielding three fractions

composed of the homocoupled product of Zn -15 (30% yield),

the title compound, and the homo-coupled product of Zn -20

(23% yield) (assignment of these products stems from LD-MS).

The second fraction was further chromatographed by SEC

(THF) to afford a red-brown solid (0.071 g, 45% yield): ¹H NMR

(CDCl₃) δ 1.44 (s, 72H), 7.65-7.75 (m, 4H), 7.80-8.40 (m, 23

H), 8.72 (d, 4H, J ) 4.2 Hz), 8.95-9.10 (m, 8H); LD-MS obsd

1932.8; FAB-MS obsd 1922.66, calcd exact mass 1922.66

(C₁₁₈H₁₁₁N₁₀IZn₂); λ_abs422, 462, 560 nm.

Iod o-Bis(p or p h yr in )-P h th a lon itr ile (26). A solution of

Zn -26 (0.050 g, 0.02 mmol) in CH₂Cl₂/TFA (4:1) was stirred

overnight. The crude reaction mixture was then washed with

0.1 M NaOH (100 mL), dried (Na₂SO₄), and chromatographed

(alumina, CH₂Cl₂/hexanes, 1:1) affording a brown solid (0.044

g, 95% yield): ¹H NMR δ -2.17 (s, 2H), -2.15 (s, 2H), 1.45 (s,

72H), 7.70-7.80 (m, 4H), 7.85-8.40 (m, 23 H), 8.64 (d, 4H, J

) 5.1 Hz), 8.85-9.00 (m, 8H); LD-MS obsd 1803.5; FAB-MS

obsd 1798.84, calcd exact mass 1798.84 (C₁₁₈H₁₁₅N₁₀I); λ_abs(log

ꢀ) 419 (5.26), 457 (5.32), 525 (4.66), 596, 655 nm.

P er ylen e-Bis(zin c p or p h yr in )-P h th a lon itr ile (Zn -27).

Following a general Pd-coupling procedure,³²a mixture of Zn -

26 (0.060 g, 0.031 mmol), ethynylperylene 9 (0.017 g, 0.031

mmol), Pd₂(dba)₃(0.005 g, 5 µmol), and P(o-tol)₃(0.011 g, 36

µmol) in toluene/triethylamine (14 mL, 5:1) was reacted in a

Schlenk flask at 35 °C for 2 h. The crude reaction mixture was

evaporated to dryness, chromatographed (silica, CH₂Cl₂/hex-

anes, 3:1), and chromatographed (SEC, THF) to afford a purple

solid (0.059 g, 82% yield): ¹H NMR δ 1.33 (s, 9H), 1.34 (s, 9H),

1.44 (s, 36H), 1.45 (s, 36H), 7.06 (d, 2H, J ) 2.1 Hz), 7.27-

7.63 (m, 3H), 7.69-7.75 (m, 4H), 7.80-8.20 (m, 20H), 8.30-

8.80 (m, 15H), 8.95-9.15 (m, 8H); LD-MS obsd 2337.3; FAB-

MS obsd 2327.97, calcd exact mass 2327.99 (C₁₅₆H₁₄₁N₁₁O₂Zn₂);

λ_abs422, 463, 560, 604 nm; λ_em625, 657 nm.

P er ylen e-Bis(p or p h yr in )-P h th a lon itr ile (27). A solu-

tion of Zn -27 (0.010 g, 4.3 µmol) in CH₂Cl₂/TFA (4:1) was

stirred overnight. The crude reaction mixture was then washed

with 0.1 M NaOH (50 mL), dried (Na₂SO₄), and chromato-

graphed (alumina, CH₂Cl₂/hexanes, 1:1), affording a reddish-

brown solid (0.075 g, 80% yield): ¹H NMR δ -2.15 (s, 2H),

-2.13 (s, 2H), 1.33 (s, 9H), 1.35 (s, 9H), 1.44 (s, 36H), 1.45 (s,

36H), 7.05 (d, 2H, J ) 2.1 Hz), 7.27-7.65 (m, 3H), 7.70-7.75

(m, 4H), 7.80-8.20 (m, 20H), 8.30-8.80 (m, 15H), 8.85-9.00

(m, 8H); LD-MS obsd 2214.7; FAB-MS obsd 2204.15, calcd

exact mass 2204.16 (C₁₅₆H₁₄₅N₁₁O₂); λ_abs(log ꢀ) 419 (5.34), 457

(5.38), 530 (5.08), 597 (4.38), 656 (4.18) nm; λ_em636, 728 nm.

Iod o-Bis(p or p h yr in )-P h th a locya n in e (28). Following

a standard procedure,^1,34a solution of pentanol (5 mL) was

treated with lithium ribbon (0.061 g, 8.8 mmol) and the

reaction mixture was stirred at ∼90 °C until the lithium had

reacted. The reaction mixture was cooled to room temperature

and 25 (0.025 g, 14 µmol) and 4-tert-butylphthalonitrile (0.023

g, 0.13 mmol) were added; then the reaction mixture was

heated to 145 °C and stirred for 3 h. The reaction mixture was

cooled to room temperature, dissolved in CH₂Cl₂, washed with

H₂O/MeOH (100 mL, 1:1), dried (Na₂SO₄), chromatographed

(silica, toluene), chromatographed (SEC, THF), and chromato-

graphed (silica, toluene) to afford a green solid (0.010 g, 30%).

¹H NMR (500 MHz) δ -3.1 to -2.4 (m, 2H), -2.10 to -2.00

(m, 4H), 1.45 (s, 36H), 1.47 (s, 36H), 1.96 (m, 27H), 7.65-9.30

(m, 48H)]; LD-MS obsd 2360.1; FAB-MS obsd 2353.12, calcd

exact mass 2353.15 (C₁₅₄H₁₅₃N₁₆I); λ_abs(log ꢀ) 418 (5.38), 456

(5.43), 526 (4.78), 608 (4.63), 674 (5.15), 696 (5.11) nm.

Meso,Meso-Lin k ed Bis(zin c p or p h yr in ) (Zn -30). Fol-

lowing a slight modification²⁹of a procedure developed by

Osuka,^17,22a solution of 29²⁹(0.030 g, 0.032 mmol) in CHCl₃

(16 mL) was treated with AgPF₆(0.031 g, 0.12 mmol) and DMA

(80 µL), and the mixture was stirred under argon for 1 h. The

crude reaction mixture was then washed with H₂O (100 mL),

dried (Na₂SO₄), and chromatographed (silica, CHCl₃), affording

a red-brown solid (0.025 g, 83% yield): ¹H NMR δ 1.46 (s, 72H),

1.59 (s, 36H), 7.65-7.90 (m, 6H), 8.05-8.25 (m, 16 H), 8.74

(d, 4H, J ) 5.1 Hz), 9.00-9.20 (m, 8H); LD-MS obsd 1880.7,

1817.7 [M⁺- Zn], 1866.0 [M⁺- 15], 1912.1 [M⁺+ 31], 1946.7

[M⁺+ 66]; FAB-MS obsd 1870.99, calcd exact mass 1870.99

(C₁₂₄H₁₄₂N₈Zn₂); λ_abs421, 460, 559 nm; λ_em623, 660 nm.

Meso,Meso-Lin k ed Bis(p or p h yr in ) (30). A solution of

Zn -30 (0.023 g, 0.012 mmol) in CH₂Cl₂/TFA (15 mL, 4:1) was

stirred overnight. The crude reaction mixture was then washed

with 0.1 M NaOH (100 mL), dried (Na₂SO₄), and chromato-

graphed (alumina, CH₂Cl₂/hexanes, 1:1), affording a brown

1

solid (0.020 g, 95% yield): H NMR δ -2.10 (s, 4H), 1.45 (s,

72H), 1.58 (s, 36H), 7.65-7.90 (m, 6H), 8.05-8.20 (m, 16 H),

8.64 (d, 4H, J ) 4.5 Hz), 8.90-9.05 (m, 8H); LD-MS obsd

1754.8; FAB-MS obsd 1747.16, calcd exact mass 1747.17

(C₁₂₄H₁₄₆N₈); λ_abs(log ꢀ) 417 (5.40), 454 (5.45), 525 (4.80), 596

(4.28), 654 (3.92) nm; λ_em662, 727 nm.

Ack n ow led gm en t. This research was supported by

the Division of Chemical Sciences, Office of Basic

Energy Sciences, Office of Energy Research, U.S. De-

partment of Energy. Mass spectra were obtained at the

Photoinduced Energy-Transfer Cascades

J . Org. Chem., Vol. 65, No. 20, 2000 6649

compounds, fluorescence spectra for perylenes 9 and 10, and

LD-MS, absorption, and fluorescence spectra for all porphyrin

containing compounds. This material is available free of charge

via the Internet at http://pubs.acs.org.

Mass Spectrometry Laboratory for Biotechnology at

North Carolina State University. Partial funding for the

Facility was obtained from the North Carolina Biotech-

nology Center and the NSF.

Su p p or tin g In for m a tion Ava ila ble: ¹H NMR for all new

compounds (except 25), absorption spectra for all perylene

J O0007940

Article Doi

A Tightly Coupled Linear Array of Perylene, Bis(Porphyrin), and Phthalocyanine Units that Functions as a Photoinduced Energy-Transfer Cascade

DOI: 10.1021/jo0007940

Source and publish data:

Authors:

Article abstract of DOI:10.1021/jo0007940

Full text of DOI:10.1021/jo0007940

Products guided by the article

R&D Labs maybe for 303089-35-2

Relevant to this article

Hot Product