Triaryl-1,3,5-triazinane-2,4,6-triones (Isocyanurates) peripherally functionalized by donor groups: Synthesis and study of their linear and nonlinear optical properties

FULL PAPER

DOI: 10.1002/chem.201200484

Triaryl-1,3,5-triazinane-2,4,6-triones (Isocyanurates) Peripherally

Functionalized by Donor Groups: Synthesis and Study of Their Linear and

Nonlinear Optical Properties

Gilles Argouarch,^[a]Romain Veillard,^[a]Thierry Roisnel,^[a]Anissa Amar,^{[a, b]}

Hacꢀne Meghezzi,^[b]Abdou Boucekkine,*^[a]Vincent Hugues,^{[c, d]}Olivier Mongin,^{[a, c]}

Mireille Blanchard-Desce,*^{[c, d]}and Frꢁdꢁric Paul*^[a]

Abstract: The linear optical (LO) and

nonlinear optical (NLO) properties of

a series of isocyanurates functionalized

by donor arms at the periphery are re-

ported herein. These octupolar deriva-

tives were obtained in a straightforward

way from commercial isocyanate deriv-

atives and were fully characterized. Al-

though several of these compounds are

known, those that exhibited the largest

NLO activities are all new compounds.

In terms of second-order activity, sever-

al of these derivatives exhibit remark-

able activity/transparency tradeoffs. In

terms of third-order activity, the longer

derivatives with the stronger donor

groups (X=NH₂, NMe₂, or NPh₂) were

shown to possess significant two-

photon absorption cross sections. These

strongly luminescent derivatives exhibit

two-photon absorption cross sections

up to 410 GM. DFT computations

were also conducted to unravel their

electronic structures and to rationalize

their NLO properties. To our knowl-

edge, the present study is the first con-

cerned with the nonlinear optical prop-

erties of these original cyclotrimers.

Keywords: density functional calcu-

lations · isocyanurates · nonlinear

optics · synthetic methods · two-

photon absorbers

Introduction

ularly in the field of foams, elastomers, paints, fibers, and

surface coatings.^[2]Thus, when used as cross-linking groups

between polyurethane-based strands, isocyanurate units

allow enhancement of the flame resistance, thermal stability,

and rigidity of the resulting polymers.^[1b,3]Alternatively, as

discrete molecules, they also intervene as key precursors in

important industrial processes concerned with the synthesis

of several polyurethane copolymers, but also as activators in

the polymerization of e-caprolactam.^[4]As reactants or addi-

tives, these chemicals are often very attractive from an

atom-economy perspective because most of them can be ob-

tained in good yields and in a single step from the corre-

sponding isocyanate monomers by the use of specific cata-

lysts.^[5]Also, after proper functionalization, they have also

given rise to more original applications, such as chloride

anion receptors,^[6]drug-delivery agents,^[7]or tensioactive

building blocks.^[8]

Triazinane-2,4,6-triones, more commonly known as isocya-

nurates (A; Scheme 1), are cyclotrimeric molecules that

have attracted considerable attention in polymer chemistry

in regard to their numerous industrial applications,^[1]partic-

[a] Dr. G. Argouarch, R. Veillard, Dr. T. Roisnel, A. Amar,

Prof. A. Boucekkine, Dr. O. Mongin, Dr. F. Paul

Sciences Chimiques de Rennes, CNRS (UMR 6226)

Universitꢀ de Rennes 1, Campus de Beaulieu

35042 Rennes Cedex (France)

Fax : (+33) 02-23-23-69-39

E-mail: abdou.boucekkine@univ-rennes1.fr

frederic.paul@univ-rennes1.fr

[b] A. Amar, Prof. H. Meghezzi

Laboratoire de Thermodynamique et Modꢀlisation Molꢀculaire

USTHB

BP 32, El Alia, 16111

However, up to now, these symmetric units had attracted

only scant attention for their (nonlinear) optical proper-

ties.^[9]This lack of interest is surprising because, owing to

their planar D_3hor twisted pseudo-D₃symmetry (A;

Scheme 1), these compounds might exhibit significant

second-^[10]and third-order^[11]nonlinear optical (NLO) activi-

ties when the central electron-attracting isocyanurate core is

symmetrically decorated with electron-releasing arms, like-

wise to related structures based on 1,3,5- and 2,4,6-substitut-

ed phenyl derivatives (B; Scheme 1).^[12]In accordance with

the first expectation, we have recently shown by hyper Ra-

leigh scattering (HRS) that derivatives such as 1-X and 2-X

Bab Ezzouar Alger (Algeria)

[c] V. Hugues, Dr. O. Mongin, Dr. M. Blanchard-Desce

Chimie et Photonique Molꢀculaires, CNRS (UMR 6510)

Universitꢀ de Rennes 1, Campus de Beaulieu

35042 Rennes Cedex (France)

[d] V. Hugues, Dr. M. Blanchard-Desce

ISM, CNRS (UMR 5255)

Universitꢀ Bordeaux

33400 Talence France

Fax : (+33) 05-40-00-67-35

E-mail: mireille.blanchard-desce@u-bordeaux1.fr

Supporting information for this article is available on the WWW

under http://dx.doi.org/10.1002/chem.201200484.

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and Endo, which was solvent-

free and thus only applicable to

liquid isocyanates.^[16]Even in

the case of 1-NO₂or 1-CN, for

which the workup was compli-

cated by the low solubility, this

experimental procedure permit-

ted us to achieve high conver-

sions of isocyanates into the

corresponding isocyanurates. In

contrast to the other 1-X deriv-

atives, the amino compound 1-

NH₂was not isolated directly

from the isocyanate precursor,

but in a subsequent reaction of

a Clemmensen-type reduction

of the nitro cyclotrimer 1-NO₂

[Scheme 2, Eq. (2)]. Most of

the 1-X derivatives have been

Scheme 1. The isocyanurate core (with the nonbonding doublets on the nitrogen atoms explicitly drawn)

versus the octupolar D_3hphenyl derivatives (insert) and the target molecules. A=electron-withdrawing groups,

D=electron-releasing groups.^[13]

(X=OMe, NMe₂) possess remarkable hyperpolarizabili-

ties.^[14]Given that such octupolar structures might also pres-

ent good activities for specific third-order NLO properties,

such as two-photon absorption (TPA),^[11]we have now com-

pleted our previous report on these compounds^[14]by study-

ing their luminescence and have subsequently used their lu-

minescence to determine the TPA cross sections of selected

derivatives. Although the synthesis of some of these cyclo-

trimers has been briefly reported, a more complete account

of their synthesis is now disclosed. The experimental work

has also been complemented by DFT calculations. Such cal-

culations were useful to obtain insight into the origin of the

NLO properties of these octupolar compounds.

previously reported, but were not always extensively charac-

terized.^[17]Thus, all 1-X derivatives isolated have now been

fully characterized by usual spectroscopic analysis (i.e., IR,

Raman, and NMR spectroscopies). Mass spectrometric or/

and elemental analysis were performed on the new deriva-

tives 1-CN and 1-NH₂.

All these compounds show a diagnostic AA’BB’ pattern

1

in the H NMR spectra for the functional peripheral rings.

The presence of carbonyl groups is evidenced by the occur-

rence of a signal near d=150 ppm in the ¹³C NMR spectra.

Results

Synthesis and characterization: Although para-functional ar-

ylisocyanurates 1-X that feature electron-releasing X sub-

stituents (X=OMe, NH₂, NMe₂) at the periphery were ini-

tially targeted for their second-order NLO properties,^[14]

some derivatives that feature strongly electron-attracting

substituents, para-functional arylisocyanurates 1-X (X=

NO₂, CN), were also targeted to complete our experimental

data on these compounds. The synthesis of most of these ar-

ylisocyanurates (X=NO₂, CN Br, OMe, NMe₂) was ach-

ieved by directly cyclotrimerizing the corresponding isocya-

nates, when commercially available [Scheme 2, Eq. (1)].

Several organic or inorganic efficient catalysts have been re-

ported for this reaction.^[2g,5,15]We used cesium fluoride as

a catalyst to carry out the trimerization because it is com-

mercially available and relatively cheap.^[16]With this cata-

lyst, good yields of most of the desired isocyanurates could

be obtained in one step after chromatographic purification.

Notably, the use of nitrobenzene as a solvent allows the

medium to remain fluid during all the reaction, and even

perfectly homogeneous in most cases. In that respect, our

procedure contrasts with that previously reported by Nambu

Scheme 2. Synthesis of cyclotrimers 1-X.

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Linear and Nonlinear Optical Properties of Functionalized Isocyanurates

FULL PAPER

A very strong absorption is also observed near n˜ =1710 cm^ꢀ1

in the IR spectra, which can be attributed to one of the n_CO

stretching modes of the three carbonyl groups. This n_CO

mode is not visible in the Raman spectra. Instead, a moder-

ate-to-intense Stokes band, which also corresponds to a very

weakly absorbing mode in the

the coupling sluggish in usual organic solvents. The reaction

has therefore to be performed in DMF under rather harsh

conditions to isolate any of these tris-coupled products (3-

TMS or 2-OMe) in satisfactory yields.

IR spectra, is present near n˜ =

1770 cm^ꢀ1. On the basis of the

vibrational selection rules ap-

plied to D₃or C₃molecules, the

symmetric n_COstretch that be-

longs to A-type irreducible rep-

resentations should be essen-

tially active in the Raman spec-

tra, whereas that that belongs

to

E-type

representations

should be active in the IR spec-

tra and also weakly in the

Raman spectra.^[19]In contrast

to these predictions, we detect-

ed two modes in the IR spectra

and only one in the Raman

spectra. However, one of the

IR active n_COmodes appears to

be much weaker than the other.

Thus, we propose that the weak

mode at higher energy in the

IR spectra corresponds to the

symmetric (A-type) n_COstretch-

ing mode, whereas the other,

much more intense, would cor-

respond to the nonsymmetric

n_COstretching mode (E-type).

Beside these intensity-related

considerations, this attribution

is also supported by our DFT

calculations (see later).

Scheme 3. Synthetic routes envisioned to access the extended cyclotrimers 2-X.

We next attempted to isolate

longer homologues bearing

electron-releasing substituents

by using standard Sonogashira

coupling protocols. Two syn-

thetic routes were envisioned

(Scheme 3): either by 1) treat-

ing the tris-bromo cyclotrimer

1-Br with functional aryl al-

kynes (route A) or 2) treating

a tris-alkyne cyclotrimer 3-H

with functional aryl iodides

(route B). We decided to test

both of these routes by using

the methoxy group (X=OMe)

as a model compound. Both

synthetic routes required a So-

nogashira coupling step with 1-

Br (Scheme 4). The poor solu-

Scheme 4. Comparison of the synthetic routes A and B to obtain 2-OMe. TBAF=tetrabutylammonium fluo-

bility of this cyclotrimer renders ride. TMS=trimethylsilyl.

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A. Boucekkine, M. Blanchard-Desce, F. Paul et al.

Route A proved attractive to

access the 2-X compounds be-

cause 2-OMe was obtained in

82% after one step from 1-Br

and

para-ethynyl

anisole

(Scheme 4). We had to isolate

3-H first to test route B, which

was carried out in two steps

(Scheme 4). First, the TMS-pro-

tected compound 3-TMS was

isolated from 1-Br by using

a Sonogashira coupling. The de-

silylation of 3-TMS was next at-

tempted with sodium carbonate.

Much to our surprise, essential-

ly the corresponding carbamate

4

could be isolated (78%).

Quite likely, under these condi-

tions, ring opening of the cyclo-

trimer 3-TMS takes place si-

Scheme 5. Synthesis of the extended cyclotrimers 2-X and 5.

multaneously with deprotection

and the alkynyl carbamate 4 is

1

formed in fair yields. The latter is a new product, which was

completely characterized by mass-spectrometric, the usual

spectroscopic (IR, Raman, and NMR), and elemental analy-

sis and X-ray diffraction studies (see Figure 2b). We tried to

repeat the deprotection with TBAF. Under such conditions,

the desired intermediate 3-H could be isolated in fair yields

(55%) and was completely characterized. The structure of

this compound was also confirmed by X-ray diffraction stud-

ies (see Figure 2a). We could eventually isolate the desired

compound 2-OMe after a Sonogashira coupling with 4-io-

doanisole, but the overall yield (14%) for this route was sig-

nificantly lower than by the other route. Given the good

synthetic access to 4-ethynyl-N,N-diphenylaniline^[20]along

with the commercial availability of the other phenylalkynyl

derivatives substituted at the para position by donor groups,

this approach was not pursued, and route A was retained as

the most efficient synthetic access to the 2-X compounds.

In a similar way to 2-OMe, two 2-X homologues (X=

NH₂, NMe₂) were initially isolated in fair yields (Scheme 5).

The very low solubility of the extended amino derivative 2-

NH₂significantly complicated its characterization, which led

us to synthesize the more soluble diphenylamino derivative

2-NPh₂.

omatic region of their H NMR spectra. The presence of the

ethynylene unit is evidenced by the presence of diagnostic

¹³C NMR signals in the alkynyl region, near d=90 ppm, and

by a new n_CCmode observed in the IR and Raman spectra,

near d=2200 cm^ꢀ1. In these compounds, the symmetric (A-

type) and asymmetric (E-type) alkyne stretching modes are

apparently energetically degenerate (or nearly so) because

only one n_CCband is detected. This outcome contrasts with

the n_COmodes of 2-X, for which absorptions that resemble

those observed for the shorter homologues 1-X are detected

by Raman and IR spectroscopic analysis.

Solid-state structures: Isocyanurates 1-CN, 1-Br, and 3-H

crystallize in centrosymmetric space groups (see Fig-

AHCTUNGTREGuNNNU res 1a,b and 2a and the Experimental Section), which ex-

cludes any second-order NLO activity for these compounds

in the crystalline state. The bond lengths and angles for

these compounds appear in the usual range^[22]because they

compare well with those of previously characterized deriva-

tives (see the Supporting Information), such as 1-H,^[2e,23]1-

F,^[24]1-Cl,^[25]1-NO₂,^[18b]and 1-iPr (Table 1).^[26,27]Notably, the

C=O bond lengths are slightly longer than those of typical

ketones (1.19 ꢂ), but shorter than those of typical amides

(1.23 ꢂ), whereas the (O)C=N bond lengths are significantly

The organometallic derivative 5 featuring ferrocenyl as

a donor at each arm was also synthesized. Note that this

compound had been reported in several patents, but no de-

tails about the synthesis or characterization had been

given.^[21]Thus, all these extended cyclotrimers were exten-

sively characterized by the usual spectroscopic (IR, Raman,

and NMR) and mass spectrometric analysis. In addition,

among the new organic derivatives, 2-OMe and 2-NMe₂

were further characterized by elemental analysis.

ꢀ

lower than the peripheral N C bond lengths (ca. 1.45 ꢂ),

ꢀ

themselves shorter than typical single C N bonds

(1.48 ꢂ).^[22]Along with the overall planarity of the isocyanu-

rate ring, these bonding features indicate some mesomerism

between the dominating neutral valence-bond (VB) form

(A) and the two other VB structures (B₁and B₂) in the

ground state (Scheme 6), which imparts some “aromatic”

character to the central ring. However, based on the bond

lengths, this resonance is less pronounced in 1-X than in typ-

ical carbamate structures such as 4.

For the extended cyclotrimers 2-X, the presence of the ad-

ditional 1,4-phenylene unit at each arm was clearly estab-

lished by the appearance of a new AA’BB’ system in the ar-

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Linear and Nonlinear Optical Properties of Functionalized Isocyanurates

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Figure 2. ORTEP representation of the complexes a) 3-H and b) 4 at the

50% probability level. Hydrogen atoms of 3-H have been omitted for

ꢀ

clarity. Selected distances [ꢂ]: a) C3 C2 1.450(6), C2 C1 1.203(6);

ꢀ

b) C1 O2 1.4498(12), O2 C3 1.3477(12), C11 C12 1.4430(15), C12 C13

1.1946(16) (also see Table 1 for other bond lengths).

Figure 1. ORTEP representation of the complexes a) 1-CN and b) 1-Br at

the 50% probability level. Hydrogen atoms have been omitted for clarity.

ꢀ

Selected distances [ꢂ]: a) C7 C10 1.447(2), C10 N11 1.147(2), C27 C30

Table 1. Selected mean bond lengths and angles for the isocyanurate

cores of 1-CN, 1-Br, 3-H, and 4.

ꢀ

1.448(2), C30 N31 1.146(2), C47 C50 1.4408(19), C50 N51 1.1479(19);

ꢀ

b) C16 Br1 1.900(3), C26 Br2 1.893(3), C36 Br3 1.895(3) (also see

Table 1).

Compound

Selected bond lengths [ꢂ]

C=O

1.204ꢁ0.001 1.205ꢁ0.008 1.206(5)

1.394ꢁ0.006 1.39ꢁ0.010

1.451ꢁ0.002 1.449ꢁ0.008 1.460(5)

Selected bond angles [8]

1-CN

1-Br

3-H

4

1.2195(13)

ꢀ

N C(O)

ꢀ

C N

1.398ꢁ0.003 1.3645(13)

1.4114(13)

A close comparison between these different data sets indi-

cates no sizeable substituent effect on the bonding distances

within the isocyanurate core. This finding is understandable

in all these cyclotrimers because the peripheral phenyl rings

adopt a twisted conformation with dihedral angles that vary

between 55 and 828 in the solid state due to the steric inter-

actions between the ortho-hydrogen atoms and the three

carbonyl groups of the isocyanurate core. This conformation

clearly disfavors the p–p over-

N-C=O

122.5ꢁ0.5

122.5(3)

122.0ꢁ0.3

123.8(4)

115.9(4)

80

126.99(10)

–

170

(O)C-N-C(O) 124.7ꢁ0.1

125.5ꢁ0.1

114.8ꢁ0.8

60/65/82

N-C(O)-N

114.7ꢁ0.2

[(O)CN]₃/Ar^[a]83/54/78

[a] Dihedral angles (ꢁ58) between the aryl mean plane and the isocyanu-

rate mean plane.

lap and limits the electronic

conjugation between the pe-

ripheral

substituent

on

a branch and the central iso-

cyanurate core.

In this respect, the compari-

son between 3-H and 4 is in-

structive (Figure 2a,b) because

it reveals that the phenyl ring

in the latter compound prefers

to remain coplanar with the

Scheme 6. Limiting VB forms of the isocyanurate ring.

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A. Boucekkine, M. Blanchard-Desce, F. Paul et al.

-C(O)-N- fragment, when not sterically congested, to maxi-

mize p overlap. This quasi-planar conformation in 4 is cer-

tainly also somewhat stabilized by the formation of

a pseudo-hydrogen bond between the carbonyl oxygen atom

O4 and one of the ortho-hydrogen atoms on the aryl ring

(H···O4: ~2.3 ꢂ). This oxygen atom is mainly engaged in

a hydrogen-bonding interaction with the amide hydrogen

atom (Hn5) of a nearby molecule.^[28]Such a stabilizing inter-

molecular interaction is clearly not observed for the cyclo-

trimers, which rather develop a type of pseudo-hydrogen

bond^[28]between one or more of their carbonyl groups and

protons of nearby molecules.

derivative 1-CN (see the Supporting Information). Other-

wise, when the para-substituents become strongly electron-

releasing (X=NH₂, NMe₂), an intense absorption is detect-

ed in the range l=250–270 nm with a shoulder at a higher

wavelength (Figure 3). This absorption is bathochromically

and hyperchromically shifted with the increasing electron-

releasing power of the para-substituent. Based on these sub-

stituent-induced shifts, the most intense absorption likely

!

corresponds to a symmetry allowed p* p charge-transfer

(CT) transition, the polarization of which depends on the

nature (i.e., donor or strong acceptor) of the X substi-

tuent.^[12d]Thus, when the substituent is neutral-to-strongly

electron releasing, the CT takes place from the X substitu-

ent toward the electron-deficient isocyanurate core. The

weak shoulder, always apparent on the low-energy side, cer-

tainly corresponds to a weakly allowed transition. The latter

One-photon absorption (OPA) studies: The linear absorp-

tion properties of isocyanurates were subsequently investi-

gated by UV/Vis spectroscopy. Most of the 1-X and 2-X

molecules possess a good transparency in the visible range

because these compounds have their lowest lying absorption

below l=400 nm (Table 2). As a result, the 1-X compounds

are all colorless in solution, except for the nitro compound

1-NO₂, which is slightly yellowish. The lowest-lying absorp-

tion maximum of these molecules depends on the nature of

the peripheral substituents and the length of the conjugated

arms. The shorter cyclotrimers 1-X that present poorly elec-

tron-withdrawing or electron-releasing substituents (i.e, Br,

H, Me) have only a weak absorption that can be detected in

the UV range as a shoulder above l=250 nm. For the more

electron-withdrawing substituents (i.e., NO₂, CN), an in-

tense absorption is present below l=265 nm, which features

a weak shoulder, near l=340 nm for 1-NO₂, whereas a dis-

tinct weaker peak is detected near l=281 nm for the cyano

!

is likely a carbonyl p* n transition according to DFT (see

Figure 3. UV/Vis spectra for selected derivatives 1-X, 2-X, and 5 in di-

chloromethane (T=208C).

Table 2. Absorption and emission properties of selected cyclotrimers in dichloromethane at 258C.

Cmpd

l_abs

e_max(ꢃ10^ꢀ3

[m^ꢀ1cm^ꢀ1

)

l_em

f^[a]

Stokes shift

DFT^[c]

l_max[nm] (f )

CH₂Cl₂

[b]

[nm]

G

]

[nm]

G

]

l_max[nm] (f )

vacuum

l_em[nm] (f)

CH₂Cl₂

1- OMe

1-NH₂

272 (sh)

234

286 (sh)

248

316 (sh)

270

316

300

264

254

326

272

352

288

364

294

278 (sh)

251

4.1

25.0

6.5

54.2

8.5

297

320

350

348

0.006

–

0.010

–

0.011

–

0.025

3100

–

3700

–

3100

–

4600

–

243 (0.0006)

220 (0.13)

256 (0.0004)

224 (0.20)

269 (0.0003)

239 (0.22)

324 (1.87)

–

247 (0.0002)

220 (0.19)

261 (0.0006)

229 (0.24)

275 (0.0013)

250 (0.58)

333 (2.03)

–

n.c.^[d]

1-NMe₂

2-OMe

n.c.^[d]

58.2

106.4

104.4

44.4

97.6

44.0

109.6

34.1

99.0

56.4

5.5

394 (1.87)

–

245 (0.05)

247 (0.12)

2-NH₂

2-NMe₂

2-NPh₂

3-H

396

418

437

301

NF^[e]

0.056

0.200

0.730

5400

–

4500

–

4600

–

2800

–

335 (1.70)

253 (0.04)

349 (1.88)

264 (0.16)

388 (1.90)

296 (0.75)

256 (0.07)

249 (0.47)

n.c.^[d]

336 (1.74)

254 (0.13)

375 (2.00)

266 (0.49)

404 (1.95)

298 (0.80)

412 (0.25)

423 (1.91)

472 (1.16)

[f]

0.025

–

74.3

2.7

253 (0.49)

311 (0.98)

n.c.^[d]

5

436

–

n.c.^[d]

342 (sh)

307

260

11.4

57.0

66.4

[a] Fluorescence quantum yield in CH₂Cl₂when excited at l_abs(quinine bisulfate in H₂SO₄(0.5m) was used as a standard). [b] Stokes shift=

(1/l_absꢀ1/l_em). [c] f=oscillator strength. [d] n.c.=not computed. [e] NF=no fluorescence detected. [f] Not found by DFT.

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Linear and Nonlinear Optical Properties of Functionalized Isocyanurates

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!

the Computational section). When the unsaturated arms are

extended, that is, when progressing from 1-X to 2-X for

a given electron-releasing substituent, further bathochromic

and hyperchromic shifts are observed for this transition, and

the intense band of the 2-X cyclotrimer now overlaps with

the low-energy absorption that appears as a shoulder in the

1-X homologues.^[29]In spite of its shift, the absorption at the

longest wavelength remains in the UV range in line with the

colorless appearance of these compounds in solution, except

for 2-NPh₂, which is faint yellow.

groups; Table 2). This transition, ascribable to the p*

n

transition, appears as a shoulder on the low-energy side of

the main absorption band for the 1-X cyclotrimers (see

Figure 3 and the Supporting Information). For a given X

substituent, the extended compounds 2-X are always more

emissive than the smaller compounds 1-X; furthermore,

among the 2-X derivatives, those with the most electron-re-

leasing X substituents are more luminescent. They also pres-

!

ent the most marked redshifts of the p* p transition,

which becomes the lowest-energy transition in these deriva-

tives (X=NR₂). An increase in the length of the p-electron

system that connects the isocyanurate core to the peripheral

X substituents also induces a bathochromic shift of the emis-

sion band and a marked increase in the quantum yields (up

to 73% for 2-NPh₂). In contrast to these purely organic de-

rivatives, metallated complex 5 was not luminescent at all.

The luminescence of this particular compound is possibly

quenched by electron transfer from the electroactive ferro-

cenyl groups.^[32]

In contrast to the organic derivatives, the tris-ferrocenyl

compound 5 has an intense brown–orange color in solution.

This color is attributable to a weak absorption observed at

l=436 nm for this complex, which possibly corresponds to

!

ferrocenyl-based d d transitions.^[30]On the basis of previ-

ous reports, the absorption at l=342 nm could typically cor-

!

respond to a (p*)_CTd_Femetal-to-ligand charge-transfer

(MLCT) transition, whereas the intense absorptions near

l=310 nm and its shoulder may be attributed to MLCT pro-

cesses. Finally, in connection with the substituent effect pre-

viously discussed for the 1-X cyclotrimers, it is tempting to

Solvatochromism: In line with the absence of a permanent

dipole moment in these molecules in the ground state,

quasi-negligible solvatochromic behavior could be stated for

the absorption of most of the 1-X derivatives (see Figure 5

!

assign the absorption detected at l=260 nm to a p*

p

transition similar to that observed for 3-H at l=251 nm.

Indeed, based on well-known electronic substituent ef-

fects,^[31]the ferrocenyl group is more electron releasing than

a hydrogen atom and could lead to a bathochromic shift of

this band.

Luminescence studies: The cyclotrimer families 1-X and 2-X

also proved to be luminescent, their luminescence being

strongly dependent on the size and on the nature of X (see

Figure 4, Table 2, and the Supporting Information). Thus,

compounds 1-X exhibit low fluorescence quantum yields (<

!

1%), in agreement with the lowest-lying p* n transition.

Increasing the electron-releasing character of the peripheral

X substituents leads to a bathochromic shift of the intense

emission band and a small increase in the fluorescence

quantum yield from 0.4–0.5% for the Me and H groups to

1.1–1.2% for the amino groups. The latter parallels the in-

crease in the molar extinction coefficients observed for the

lowest-lying intense transition (i.e., from 800–1000m^ꢀ1cm^ꢀ1

for H and Me groups to 6000–7000m^ꢀ1cm^ꢀ1for the amino

Figure 5. Solvatochromic absorption and emission behavior of 2-NPh₂in

various solvents (T=258C).

and the Supporting Information).^[33]A very slight solvato-

chromism is nevertheless observed in the absorption of com-

pounds 2-X featuring amino substituents. Thus, an overall

negative solvatochromism takes place for 2-NPh₂and 2-

NMe₂(Dn_max= <540 and <580 cm^ꢀ1, respectively), whereas

a larger and overall positive solvatochromism is observed

for 2-NH₂(Dn_max= <1090 cm^ꢀ1). These contrasting behav-

iors cannot be related to the purely dipolar effect of the sol-

vent and suggest that solvent specific effects are operative.

During the emission process, however, the extended cyclo-

trimers 2-X exhibit a much larger solvatochromism, as evi-

denced below for 2-NPh₂(Figure 5). An increase in the sol-

vent polarity induces a marked bathochromic shift of their

emission band. Their solvatochromic behavior follows the

Lippert–Mataga relationship^[35][see Eq. (1a) and the Sup-

porting Information] with a linear dependency of the Stokes

shift on the polarity–polarizability parameter Df [Eq. (1b)]:

Figure 4. Normalized emission spectra for selected derivatives 1-X, 2-X,

and 3-H in dichloromethane (T=208C).

Chem. Eur. J. 2012, 00, 0 – 0

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A. Boucekkine, M. Blanchard-Desce, F. Paul et al.

n_absꢀ n_em¼ 2Dm²Df=ðhca³Þ þ const

cence quantum yield is large enough for accurate determina-

tion of their TPA cross sections. Only the red edge of the

TPA band could be obtained for cyclotrimer 2-NH₂, whereas

the maximum of the TPA band was observed for 2-NMe₂

and 2-NPH₂and is located at l=720 and 740 nm, respec-

tively, with high maximum TPA cross sections (up to

410 GM). Extension of the p-conjugated connectors and an

increase in the strength of the donor terminal groups was

therefore a fruitful way not only to enhance the photolumi-

nescence properties, but also to obtain good two-photon ab-

sorbers at the beginning of the NIR range. The comparison

of the TPA band of 2-NMe₂and 2-NPh₂with their rescaled

one-photon band shows that the TPA maximum is situated

close to twice that of the OPA maximum. This comparison

also suggests that the excited states at the origin of the TPA

absorption in the NIR are also active in OPA and corre-

spond to the most intense one-photon transitions detected

at the lowest energy in the UV range (see the Supporting

Information).

ð1aÞ

~

where, n_absand n_emare the wavenumbers of the absorption

and fluorescence maxima, respectively; h is the Planck con-

stant; c is the light velocity; a is the radius of the solute

spherical cavity; Dm is the change of dipole moment be-

tween the ground state and the emitting excited state; and

Df is defined as:

Df ¼ ðeꢀ1Þ=ð2e þ 1Þꢀðn²ꢀ1Þ=ð2n²þ 1Þ

ð1bÞ

where e is the dielectric constant and n is the refractive

index of the solvent. This behavior, already reported earlier

for other octupolar derivatives built from a triphenylamine

core,^[36]is indicative of a highly polar emissive excited state

that results from excitation localization on a dipolar branch

after excitation, prior to emission.^[37]

Two-photon absorption (TPA) studies: By using the lumi-

nescence of these compounds, we tried to determine their

TPA cross sections in the near-IR (NIR) range (l=700–

1000 nm) through investigation of their two-photon excited

fluorescence (TPEF). The excitation was performed with

femtosecond pulses from a Ti:sapphire laser (Figure 6 and

Table 3). However, due to instrumental limitations, no

TPEF could be detected for many of these compounds in

the available spectral range of the laser because the 1-X cy-

clotrimers have their OPA below l=350 nm (which is also

the case for 2-OMe). In contrast, the amino derivatives 2-X

exhibit significant TPEF in the NIR range, and their fluores-

DFT calculations: Compounds 1-OMe, 1-NH₂, 1-NMe₂, 3-H,

2-OMe, 2-NH₂, 2-NMe₂, 2-NPh₂, and 3-H were employed

for the DFT calculations (see the Computational Details).

The solid-state geometry found for 3-H (Table 1) was used

to generate the various structures before optimization,

which was then performed without symmetry constraints for

all the derivatives. For calculation purposes (see later), the

structure of the isocyanuric acid trimer 6 (Scheme 1; R=H

for A) was also derived from 3-H and optimized.

For the model compound 3-H, the calculated geometric

parameters compare well with the experimental data (see

Table 1 and the Supporting Information). The three periph-

eral 4-phenylethynyl substituents adopt a tilted conforma-

tion relative to the isocyanurate mean plane in the opti-

mized geometry, thus resulting in a pseudo-D₃symmetry,

very similar to the D₃geometry observed in the solid-state

structure of this compound (Figure 7). The experimental C8-

C7-N3-C4 dihedral angle is ꢀ83.418, and the calculated

angles are ꢀ67.69 and ꢀ89.308 in the gas phase and di-

chloromethane, respectively. Notably, the computed parame-

ters in a dielectric continuum that correspond to dichloro-

Figure 6. TPA spectra of 2-X (X=NH₂, NMe₂, NPh₂) in dichloromethane

(T=258C) in the NIR range.

Table 3. TPA properties of selected cyclotrimers in dichloromethane at

258C.

[a]

[b]

[c]

[e]

Cmpd

l_OPA

l_TPA

s₂

s₂/MW^[d]

[GMg^ꢀ1

fꢃs₂

[nm]

[GM]

G

]

[GM]

2-NH₂

2-NMe₂

2-NPh₂

326

352

364

ꢂ700

720

740

ꢃ45

360

410

ꢃ0.06

>2.5

72

300

0.458

0.354

[a] Maximum of the OPA. [b] Maximum of the TPA. [c] TPA cross sec-

tion at the maximum. [d] Figure of merit relevant for applications in opti-

cal limiting or nanofabrication.^[38][e] Two-photon brightness relevant

figure of merit for imaging applications. f=luminescence quantum yield,

MW=molecular weight.

Figure 7. Optimized geometry of 3-H.

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Linear and Nonlinear Optical Properties of Functionalized Isocyanurates

FULL PAPER

methane are closer to the experimental data than those ob-

tained in the gas phase. Indeed, the mean deviations in the

gas phase and solution are 0.008 and 0.007 ꢂ for the bond

lengths, 1.40 and 0.928 for the bond angles, and 3.08 and

1.858 for the torsion angles, respectively.

With the exception of the methoxy derivatives 1-OMe

and 2-OMe, which featured differently oriented methoxy

groups, pseudo-D₃geometries were also found for all the

other compounds after optimization without symmetry con-

straints. In the case of the extended compounds 2-OMe, 2-

NH₂, 2-NMe₂, and 2-NPh₂, the two phenyl rings remain co-

planar within each arm and each arm adopts a similarly

tilted conformation relative to the central isocyanurate core.

As expected from the overall symmetry of these molecules,

the dipole moment in their ground state is essentially zero,

except for the compounds that bear methoxy groups.

Indeed, the latter rotate during the optimization procedure

and give rise to slight dipole moments in the range 1.5–

2.0 D with large out-of-plane contributions (Table 4). A

comparison between the computed vibrational modes and

experimental values also proved satisfactory because they

confirmed the attribution proposed for the isocyanurate-

based n_COmodes (see the Supporting Information).

Figure 8. Frontier molecular orbitals of 3-H (optimized geometry).

LUMO+2 belongs to a totally symmetric representation

(A) and essentially results from a combination of p* MOs

of the first phenyl rings connected to the isocyanurate core.

For the longer compounds 2-OMe, 2-NMe₂, and 2-NPh₂, the

HOMO is rather similar and now includes the alkynyl bond

(Figure 9b). As a result, the weight of the terminal donor

atom slightly decreases relative to the shorter compounds

(9, 18, and 26% for 2-OMe, 2-NH₂, and 2-NMe₂, respective-

ly). More in contrast to the 1-X compounds, the LUMO to

LUMO+2 are now essentially located on the p manifold of

the peripheral arms, and do not include any sizeable (p_CO)*

character.

Table 4. Calculated dipole moments and HOMO–LUMO gaps for 1-

OMe, 1-NH₂, 1-NMe₂, 2-OMe, 2-NH₂, 2-NMe_2,2-NPh₂, and 3-H.

Cmpd

m [D]

HOMO–LUMO gap [eV]

Vacuum

1.33

0.31

0.20

1.49

0.56

0.41

0.03

0.00

CH₂Cl₂

1.65

0.38

0.03

1.70

0.07

0.63

0.08

0.01

vacuum

CH₂Cl₂

5.70

5.47

4.92

4.09

3.81

3.61

3.46

5.26

1-OMe

1-NH₂

1-NMe₂

2-OMe

2-NH₂

2-NMe₂

2-NPh₂

3-H

5.74

5.58

5.21

4.12

3.98

3.82

3.56

5.20

Rather large HOMO–LUMO gaps separate the empty

antibonding MOs from the HOMOs (5.74–5.20 eV) in the

shortest cyclotrimers 1-X and 3-H. This gap progressively

decreases upon elongation of the p manifold on the periph-

eral arms, that is, when progressing from 1-X to 2-X. The

gap also decreases among each series, especially when more

and more electron-releasing substituents are present on the

periphery (Table 4), thereby mirroring the variation in

energy of the lowest-lying intense absorptions of these com-

pounds (Table 2).

Although the models studied were optimized without

symmetry constraints, and therefore no longer belonged to

the D_3hsymmetry group to which the idealized starting ge-

ometry belonged, the local (C₃) pseudosymmetry around the

isocyanurate core allows recognition of MOs that would

belong to the A or E representations with the C₃symmetry.

Thus, as with 3-H, the HOMOs of 1-OMe, 1-NH₂, and 1-

NMe₂belong to the symmetric (A) representation with p-

type MOs that are essentially located on the periphery of

each cyclotrimer and present a sizeable weight on the donor

substituent (ca. 23, 30, and 44% for 1-OMe, 1-NH₂, and 1-

NMe₂, respectively; Figure 8). HOMO-1 and HOMO-2 are

nearly degenerate in energy and can be identified with two

sister MOs that would belong to an E irreductible represen-

tation under an ideal C₃or D₃symmetry (Figure 9a). The

LUMO and LUMO+1 of these compounds also seem to

constitute a degenerate pair of E-type MOs that are essen-

tially p based, but also heavily weighted on the carbonyl an-

tibonding (p_CO)* and somewhat on the p* MOs of the first

phenyl ring linked to the isocyanurate core. In contrast,

The lower-lying electronic transitions were then derived

by time-dependent DFT (TD-DFT) calculations under

vacuum and in dichloromethane (see the Supporting Infor-

mation). Consideration of a dielectric continuum around the

molecules results in a change in the nature of the low-

energy transitions for the 1-X and 3-H systems and in

a slight improvement in the overall oscillator strength,

which is inline with non-negligible solvation effects. The first

intense (f>0.13) transition corresponds to a symmetry-al-

!

lowed p* p transition (E A). The main character of this

transition is the transfer of electron density between essen-

Chem. Eur. J. 2012, 00, 0 – 0

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A. Boucekkine, M. Blanchard-Desce, F. Paul et al.

Also, emission energies from

the relaxed excited-state geom-

etry were computed for 2-X

and 3-H in dichloromethane

(see Table 2 and the Supporting

Information). The computed

wavelengths

and

oscillator

strengths correspond to an

emission from the relaxed first

singlet excited state, and the

optimized geometry was com-

puted by using TD-DFT calcu-

lations. According to these cal-

culations,

a strongly allowed

emission should be observed

above l=350 nm for 2-OMe, 2-

NMe₂, and 2-NPh₂. All these

emissions

originate

from

LUMO!HOMO

transitions.

Again, in terms of energies, the

TD-DFT results correlate nicely

with the experimental data

(Table 2), albeit slightly overes-

timated for each compound.

Also, the oscillator strengths

computed for these compounds

Figure 9. Energy diagram of the molecular frontier orbitals of the a) 1-NMe₂and b) 2-NMe₂systems in their

optimized geometry.

tially phenyl-based p manifolds on each arm from the pe-

riphery toward the center of the compound, with some

(p_CO)* character present in the vacant MOs, but only in the

shortest compounds (i.e., 1-X and 3-H). For 2-X compounds,

(especially 2-OMe and 2-NPh₂) do not always reflect the

quantum yields measured experimentally in dichlorome-

thane. These discrepancies might originate from the fact

that the true emitting state was not always found by using

our computational procedure. Alternatively, by considering

!

an increase in the overall p* p character of this transition

!

within each arm is stated relative to the shorter homologues

1-X (X=OMe, NH₂, NMe₂). According to calculations, al-

though this transition involves the very frontier MOs in the

longer compounds (2-X), this transition does not correspond

to the HOMO–LUMO transition for the shorter compounds

(1-X) and also does not correspond to the experimentally

detected shoulder that appears on the low-energy edge of

their lowest-lying intense absorption. The latter might be at-

the energetic proximity between the (p*)_COn_Oand LU-

!

MO HOMO states in these cyclotrimers, if the former is

!

tributed to weakly allowed transitions of (p*)_COn_Ocharac-

ter, more specific to the isocyanurate core. Their exact

nature was more easily unraveled by TD-DFT computations

performed on model compound 6, which lacks peripheral

phenyl groups (Figure 10) and is a model that plainly dem-

!

onstrates these LUMO HOMO and LUMO+1 HOMO

transitions that are partly forbidden by symmetry. The wave-

length of these transitions was computed to be at l=214 nm

!

for 6. For the longer derivatives 2-X, a second weaker E

A

!

transition energy (LUMO HOMO-3 and LUMO+

!

1

HOMO-3) should in principle take place at higher

energy, as experimentally observed. Thus, the effects of the

arms extension and the substituents on these transitions are

qualitatively well reproduced. Overall, the match with our

experimental observations is good (Table 2) and, qualitative-

ly, the effect of the arms extension and electronic substitu-

ent effects on these transitions is well reproduced.

Figure 10. Frontier MOs of 6 (D_3hsymmetry): a) HOMO, b) LUMO, and

c) LUMO+1.

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Linear and Nonlinear Optical Properties of Functionalized Isocyanurates

FULL PAPER

slightly more stabilized in the real compounds than in the

computations, lower radiative rates will result. Then, in con-

nection with the strong solvatochromism observed in the

emission (see Figure 5 and the Supporting Information),

DFT computations reveal the buildup of polarity oriented

along one of the arms of the cyclotrimer that accompanies

the vibronic relaxation in the gas phase of the first excited

singlet.^[11a,37b]Due to this process, the dipole moments in-

crease significantly relative to the ground state from 1.49 to

7.28 D for 2-OMe and from 0.41 D to 11.78 D for 2-NMe₂.

Finally, the hyperpolarizabilities were computed by finite

differences with B3LYP/6-31G* calculations (Table 5) and

by using AM1 calculations (see the Supporting Informa-

tion).^[39]The solvent polarity seems to have only a moderate

influence on the b values computed, except for 2-OMe and

2-NPh₂, for which significantly larger hyperpolarizabilities

were found in dichloromethane.

lower in energy. Accordingly, TD-DFT computations con-

firm that the strong transition detected each time for 1-X or

!

3-H cyclotrimers corresponds to a E A-type transition,

whereas the shoulder detected at lower energy is assigned to

!

forbidden (p*)_COn_Otransitions. The intense (allowed)

E

!

A transition is controlled by the nature of the donor

groups and by the length of the conjugated arms. Thus, in-

creasing the electron-releasing power of the X substituent

raises the HOMO energy, thereby decreasing the HOMO/

LUMO gap. Alternatively, upon extension of the arms, the

(p*)_COcharacter of the LUMO decreases concomitantly

with an increase in ethynyl character for both the HOMO

and LUMO. These electronic effects contribute to a decrease

in the HOMO–LUMO gap and, while shifting the corre-

!

sponding p* p transition to lower energies, strengthen its

arm-centered character. However, this transition remains in

the UV range for all the organic cyclotrimers tested so far,

even the extended ones that

feature amino substituents. As

a result, 1-X and 2-X present

a good transparency range in

the visible range, with only

a slight yellowish color being

observed for 2-NPh₂in solu-

tion. In line with their quasi-

nonpolar ground state, a very

weak solvatochromism is ob-

served in absorption.

Table 5. Molecular hyperpolarizabilities and related experimental (HRS at l=1907 or 1064 nm)^[14]and theo-

retical DFT data derived for selected cyclotrimers in dichloromethane.

[a]

[b]

Cmpd

l_max

b_HRS

b_HRS(0)^[c]

j jbj j

j jb₀j j

b_DFT(0)^[d]

j jb₀j j/MW^[e]

[nm]

[10^ꢀ30esu]

vacuum

CH₂Cl₂

[10^ꢀ32esug^ꢀ1

]

1-OMe

1-NH₂

1-NMe₂

2-OMe

2-NH₂

228

248

270

316

326

352

362

19^[f]

–

15^[f]

–

62

–

178

104

–

48

–

161

61

–

178

209

0.2

0.6

1.5

13.9

20.2

32.5

50.4

0.3

0.8

2.2

24.9

26.8

32.7

98.9

0.107 ACTHNGUTRENNU(G 0.001)

[g]

–

ACHTUNGTRENNUNG

55

50

0.330

0.082

–

ACHTUNGTRENNUNG

32^[f]

19^[f]

ACHTUNGTRENNUNG

[g]

–

ACHTUNGTRENNUNG

2-NMe₂

2-NPh₂

66

78

55

64

214

253

0.227

0.180

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

[a] In solution with CH₂Cl₂. [b] The precision of the measurements is about ꢁ15%; ethyl violet (b=170ꢃ

10^ꢀ30esu) was used as the reference in CH₂Cl₂; correlation between SI units: b(SI)=4.172ꢃ10^ꢀ10b (esu); the

Luminescence studies reveal

reported b values are given in the b^Xconvention as defined by Willets et al.^[40][c] Calculated by using Equa- that these compounds are also

tion (2a). [d] Values calculated for vacuum and solution. [e] Values deduced from theoretical values are given

emissive, especially the longer

2-X compounds bearing strong

electron-releasing substituents.

in parenthesis. [f] The measurement was performed in CHCl₃at l=1064 nm; the solvent (b=0.19ꢃ10^ꢀ30esu)

was used as a reference at this wavelength. [g] Not determined due to low solubility.

On the basis of the TD-DFT

!

Discussion

computations, the allowed (E A) transition should popu-

late an excited state that is potentially strongly emissive and

!

Linear optical properties: Linear absorption studies reveal

that cyclotrimers such as 1-X or 2-X present an intense al-

lowed transition in the UV range, whereas a second transi-

tion at higher energy is detected for the extended deriva-

tives. The most intense transitions in the UV range for these

compounds are reproduced fairly well by nonsymmetry-re-

stricted TD-DFT calculations (Table 2), thus revealing a cor-

respondence to a symmetrical charge shift from the periph-

that presents a strong p* p CT character. The low fluores-

cence quantum yield observed for the shorter compounds is

attributed to the existence of a weakly allowed (p*)_COn_O

transition, observed as a shoulder on the lower-energy side

!

of the intense E A absorption band. Indeed, mirror

images between the absorption and emission (see the Sup-

porting Information) clearly reveal that the strongly absorb-

ing state is not the emitting state for the 1-X derivatives.

This state of lower energy in 1-X and 3-H traps the initially

!

ery toward the center of the arms, with a strong p* p char-

!

acter. A simple symmetry-based analysis (Frenkel exciton

model) of compounds that possess a trifold symmetry axis

predicts that any set of arm-localized CT transitions com-

bine to give two new symmetry-adapted transitions in such

octupolar systems.^{[11a,d,37b,41]}One transition, nondegenerate

and one-photon forbidden, belongs to an A-type irreducible

representation, and the other transition, doubly degenerate

and one-photon allowed (as well as two-photon allowed),

belongs to a E-type representation. In the absence of elec-

tronic interactions between branches, these two transitions

generated p* p CT state (through fast internal conversion)

and mostly decays in a nonradiative way to the ground state

due to the low radiative rate of the lower emissive state ac-

cording to the Strickler–Berg equation.^[42]However, exten-

sion of the conjugation path within each arm and peripheral

functionalization with donor groups bathochromically shifts

the p* p CT state, whereas the (p*)_COn_Otransition re-

mains unaffected. As a result, the strongly allowed (E A)

transition becomes the lowest-energy transition, thus leading

to strong emission for compounds 2-X bearing strongly elec-

tron-releasing substituents. In agreement with the absence

of a shoulder on the low-energy side in the absorption spec-

!

should take place at the same energy, but in case of a size-

!

able electronic coupling, the E A-type transition should be

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A. Boucekkine, M. Blanchard-Desce, F. Paul et al.

tra of these compounds, the radiative decay dominates the

de-excitation pathways of the excited state. For the latter

compounds, the marked positive solvatochromism stated in

the emission gives rise to large slopes in the corresponding

Lippert–Mataga plots. This behavior is indicative of a highly

polar emissive excited-state that results from the localization

of the excitation on one of the dipolar arms, as previously

observed for other types of octupolar systems.^[36,37]DFT cal-

culations on the excited states agree with such an interpreta-

tion.

theoretical values have precedence.^[39,46]The mismatch with

DFT values is most pronounced for the shorter compounds

(1-X), but diminishes for the longer cyclotrimers (2-X). The

AM1 calculations performed for these compounds also give

overall lower values than the experimental values, but the

molecular hyperpolarizabilities of the 1-X and 2-X com-

pounds lie much closer (see the Supporting Information).

Actually, the main discrepancy between the experiment and

calculations resides in the inverse order found for the mo-

lecular hyperpolarizabilities of 1-NMe₂and 2-OMe.

The classic figures of merit (j jb₀j j/MW; MW=molecular

weight) were also calculated for these compounds (Table 5).

These data allow for comparison between different symme-

tries and sizes through MW normalization. On the basis of

the experimental values, these figures of merit suggest that

functionalizing the shorter 1-X derivatives by strong donors

(such as in 1-NMe₂) constitute a better strategy to improve

the NLO response of these compounds than synthesizing cy-

clotrimers with extended arms such as 2-X. As previously

discussed,^[14]the hyperpolarizabilites determined for 1-X

(X=OMe, NMe₂) and 2-X (X=OMe, NMe₂, NPh₂) are far

from negligible when reported relative to the size of the

molecules and stand comparison with the b₀values reported

for related octupoles (Scheme 7).^[13]Without surprise, these

derivatives present a much better hyperpolarizability than

that previously determined for 11, which features electron-

Nonlinear optical properties: The hyperpolarizabilities of

the cyclotrimers 1-X and 2-X featuring electron-releasing

groups at their periphery have been previously determined

by the hyper Raleigh scattering (HRS) method in solution

(Table 5), except for 1-NH₂and 2-NH₂which turned out to

be not soluble enough.^[14]The corresponding static hyperpo-

larizabilities, denoted as b_HRS(0) hereafter, were determined

by using the simple three-level model [Eqs. (2a) and

(2b)].^[10c,43]With an incident beam at 1907 nm (or 1064 nm),

the difference between dynamic (b) and static hyperpolari-

zabilites (b₀) remains small for most of these compounds.

The corresponding orientationally averaged hyperpolariza-

bilities (hb²i) were evaluated along with the modulus of the

2

hyperpolarizability tensor (j jbj j =[ꢀ_ijkb_ijk

]

^1/2), considering

an idealized D_3hor D₃symmetry for these NLO-phores and

assuming that j jbj j was essen-

tially dominated by the in-plane

longitudinal components (j jbj j

=2j jb_zzzj j) [Eq. (3)].^[10c,43]

2

b ¼ b₀½E₀₁²=ðE₀₁ꢀ4ꢁh²w²ÞðE₀₁ꢀꢁh²w²Þꢄ

ð2aÞ

2

ð2bÞ

ð3Þ

b₀¼ 3=2½jm₀₁j m_1ꢀ1=E₀₁

ꢄ

1=2

jb_zzzj ¼ ð21=8Þ

b

ð0Þ

HRS

An increase in the molecular

hyperpolarizabilities was stated

when increasing the donating

power of the X substituent or

when proceeding from 1-X to

2-X for a given X substituent.

The theoretical values presently

calculated by DFT reproduce

this trend, but underestimate

the values of the hyperpolariza-

bilities found experimentally

(Table 5). It is important to

point out here that our DFT

calculations do not take into ac-

count any vibrational contribu-

tion^[44]or specific solvation ef-

fects.^[45]Similar differences be-

tween the experimental and Scheme 7. Selected octupoles related to the cyclotrimers 1-X and 2-X.

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Linear and Nonlinear Optical Properties of Functionalized Isocyanurates

FULL PAPER

poorer arms and for which no conjugation was effective be-

tween the peripheral arms and the central core.^[9]Actually,

the 1-X and 2-X derivatives presently studied possess an ac-

tivity/transparency tradeoff comparable to that of the borox-

tives in which the triple bond would be replaced by

a double bond, which should result in combined redshift and

TPA enhancement.^[51]As a result, the TPA band that corre-

sponds to the intense band of the two-photon allowed

!

A transition^[37b]would be shifted in the NIR range, thus

ines 9-X previously studied by some of us.^[47]

A

Considering a classic VB model of a simple D₃compound

with three CT states, we know that TPA is symmetry al-

lowed from the ground state to both the E- and A-type

(lower and higher in energy, respectively) states.^[11a,37b,48]Ac-

cordingly, the TPA peak matches well with half of the

energy of the intense peak in the UV range also attributed

to this transition. When compared to the values determined

for other propeller-shaped octupolar derivatives of the same

size and bearing electron-releasing substituents at the pe-

riphery, the TPA cross sections found for 2-NMe₂and 2-

NPh₂are rather similar to those values reported for triaryl

benzenes such as 8-NHex₂(s₂=407 GM),^[49]but are clearly

larger than those values reported for triarylamino deriva-

tives such as 12 (s₂=30 GM;^[36a]Scheme 8). Notably, the fig-

ures of merit classically considered for application in optical

limiting or nanofabrication, such as s₂/MW (Table 3), which

were obtained for 2-NMe₂or 2-NPh₂, are comparable or

better than those values obtained for 7-NHex₂or 12.^[38c]This

outcome is however no longer the case when octupoles that

can adopt a fully conjugated planar conformation, such as

13 (s₂=2405 GM), are considered.^[50]Given that the 2-X

molecules were presently not optimized for TPA, these re-

sults are strongly encouraging to investigate the TPA prop-

erties of new analogues of these cyclotrimers further. In par-

ticular, it would be interesting to investigate related deriva-

leading to a major enhancement.^[36b]

Conclusion

For the first time, an extensive study of the linear and non-

linear optical properties of a series of isocyanurates func-

tionalized by donor arms at the periphery has been conduct-

ed. Although some of the shorter derivatives among 1-X or

5 were already known, the longer derivatives 2-X and 3-X

reported herein are new molecules that have been fully

characterized. These compounds, previously demonstrated

by some of us to present a good activity/transparency trade-

off in terms of second-order NLO activity,^[14]are readily ac-

cessible in a few steps from commercial isocyanates. We also

showed that the longer derivatives 2-X, when functionalized

with strong donor groups (X=NH₂, NMe₂, or NPh₂),

become strongly luminescent and exhibit fairly large TPA

cross sections (with s₂values up to 410 GM). DFT calcula-

tions reveal their electronic structures and confirm the

trends previously evidenced by HRS for their hyperpolariza-

bilities.^[14]The origin of these hyperpolarizabilities can be

traced to the existence a strong octupolar CT transition (of

!

E

A symmetry) from the peripheral arms toward the iso-

cyanurate core that takes place in the near-UV range. This

latter transition becomes the lowest-lying transition for the

2-X derivatives with extended arms. Although the HRS

measurements did not demonstrate basically enlarged hyper-

polarizabilities for the extended derivatives 2-X over their

1-X analogues, TPEF studies pointed out that 2-X constitute

the first members of a new class of promising biphotonic ab-

sorbers. Work is in progress to explore new derivatives of

this kind and to exploit their remarkable optical properties

in molecular-based devices.

Experimental Section

General procedures: All the manipulations were carried out in an inert

atmosphere of argon with dried and freshly distilled solvents. Commer-

cial reagents (isocyanates) were used as received. Apart from 1-H, some

[15b,d,18]

1-X cyclotrimers have been previously reported (1-NO₂

1-Br,^[15b]1-

Me,^[15a,18b]1-OMe,^[2e,15a,b]and 1-NMe₂)^[15b](see the Supporting Information

for more details).

Catalytic cyclotrimerization reaction—general procedure: In an oven-

dried Schlenk tube, cesium fluoride (2 mol%) was added to the isocya-

nate precursor dissolved in nitrobenzene (5–10 mL). The reaction mix-

ture was stirred overnight at room temperature to give, in some cases,

a pale precipitate. A mixture of diethyl ether/hexane (1:1) was added and

the crude solid formed was filtered on a fritted funnel, before being puri-

fied by flash chromatography on silica gel.

1,3,5-Tris(4-cyanophenyl)-1,3,5-triazinane-2,4,6-trione (1-CN): Following

the general procedure with 4-cyanophenylisocyanate (1 g, 6.9 mmol), CsF

(21 mg, 0.14 mmol), and ethyl acetate as the eluent for chromatography

Scheme 8. Selected two-photons absorbers related to the cyclotrimers 2-

X.

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A. Boucekkine, M. Blanchard-Desce, F. Paul et al.

3

(250 mg, 25%). ¹H NMR (200 MHz, CDCl₃, TMS): d=7.86 (d, J_H,H

=

The reaction mixture was extracted with CH₂Cl₂, washed with water, and

dried over MgSO₄. After filtration and evaporation to dryness, the crude

product was purified by column chromatography on silica gel with

CH₂Cl₂(100 mg, 38%).

8.6 Hz, 6H), 7.56 ppm (d, ³J_H,H=8.6 Hz, 6H); ¹³C{¹H} NMR (400 MHz,

CDCl₃, TMS): d=147.0, 136.3, 133.1, 129.2, 117.2, 113.8 ppm; IR (KBr):

n˜ =2229 (C N, m), 1779 (C=O, vw), 1714 cm (C=O, s); Raman: n˜ =

ꢀ1

ꢅ

ꢀ1

ꢅ

2230 (C N, vs), 1777 cm (C=O, m); UV/Vis (CH₂Cl₂): l_max(e)=281 nm

1,3,5-Tris{4-[(4-aminophenyl)ethynyl]phenyl}-1,3,5-triazinane-2,4,6-trione

(2-NH₂): Following the general procedure with 1-Br (594 mg, 1 mmol),

CuI (38 mg, 0.2 mmol), [PdCl₂ACHTNUTRGNE(NUG PPh₃)₂] (70 mg, 0.1 mmol), DMF (25 mL),

(17600 mol^ꢀ1dm³cm^ꢀ1); MS (EI): m/z calcd for C₂₄H₁₂N₆O₃: 432.0970

[M]⁺; found: 432.0965; crystals of X-ray quality were grown by slow dif-

fusion of pentane into a solution of 1-CN in acetone.

Et₃N (5 mL), and 4-ethynylaniline (585 mg, 5 mmol). The product was

purified by column chromatography eluting with a gradient of ethyl ace-

tate/hexane from 2:1 to 4:1 (320 mg, 45%). ¹H NMR (200 MHz,

1,3,5-Tris(4-bromophenyl)-1,3,5-triazinane-2,4,6-trione (1-Br): Following

the general procedure with 4-bromophenylisocyanate (4 g, 20.2 mmol),

3

CsF (61 mg, 0.4 mmol), and CH₂Cl₂as the eluent for chromatography

CD₃SOCD₃, TMS): d=7.60 (d, J_H,H=8.4 Hz, 6H), 7.46 (d, J_H,H=8.4 Hz,

3

(3.50 g, 88%). ¹H NMR (200 MHz, CD₂Cl₂, TMS): d=7.75 (d, J_H,H

=

6H), 7.24 (d, J_H,H=8.4 Hz, 6H), 6.58 (d, J_H,H=8.4 Hz, 6H), 5.65 ppm (s,

8.7 Hz, 6H), 7.35 ppm (d, ³J_H,H=8.7 Hz, 6H); ¹³C{¹H} NMR (50 MHz,

CD₂Cl₂, TMS): d=148.5, 133.2, 133.1, 130.6, 124.0 ppm; IR (KBr): n˜ =

1776 (C=O, vw), 1719 cm^ꢀ1(C=O, vs); Raman: n˜ =1772 cm^ꢀ1(C=O, s);

l_max(e)= <230 (ꢃ40000), 264 nm (1520 mol^ꢀ1dm³cm^ꢀ1); UV/Vis

(CH₂Cl₂): l_max(e): 264 nm (1520 mol^ꢀ1dm³cm^ꢀ1); HRMS (EI) m/z calcd

for C₂₁H₁₂N₃O₃Br₃: 592.8408 [M]⁺; found: 592.8397; elemental analysis

calcd (%) for C₂₁H₁₂N₃O₃Br₃: C 42.46, H 2.04, N 7.07; found: C 42.24, H

2.07, N 6.97; crystals of X-ray quality were grown by slow evaporation of

a solution of 1-Br in CH₂Cl₂.

6H); ¹³C{¹H} NMR (50 MHz, CD₃SOCD₃, TMS): d=150.6, 149.5, 134.5,

133.6, 132.2, 130.0, 124.8, 114.4, 108.5, 93.3, 86.7 ppm; IR (KBr): n˜ =2211

ꢀ1

ꢅ

(C C, m), 1778 (C=O, vw), 1777 cm (C=O, vw); Raman: n˜ =2208 (C

C, m), 1777 cm^ꢀ1(C=O, vw); HRMS (EI): m/z calcd for C₄₅H₃₁N₆O₃:

703.2457 [M+H]⁺; found: 703.2464.

1,3,5-Tris(4-{[4-(dimethylamino)phenyl]ethynyl}phenyl)-1,3,5-triazinane-

2,4,6-trione (2-NMe₂): Following the general procedure with 1-Br

(300 mg, 0.5 mmol), CuI (19 mg, 0.1 mmol), [PdCl₂ACHTUNTRGENUNG(PPh₃)₂] (35 mg,

0.05 mmol), DMF (20 mL), Et₃N (5 mL), and 4-ethynyl-N,N-dimethylani-

line (367 mg, 2.5 mmol). The product was purified by column chromatog-

raphy with CH₂Cl₂(200 mg, 50%). ¹H NMR (200 MHz, CDCl₃, TMS):

d=7.64 (d, ³J_H,H=8.4 Hz, 6H), 7.45 (d, ³J_H,H=8.8 Hz, 6H), 7.38 (d,

³J_H,H=8.4 Hz, 6H), 6.71 (d, ³J_H,H=8.8 Hz, 6H), 3.03 ppm (s, 18H);

¹³C{¹H} NMR (50 MHz, CDCl₃, TMS): d=150.6, 148.7, 133.2, 132.6,

1,3,5-Tris(4-aminophenyl)-1,3,5-triazinane-2,4,6-trione (1-NH₂) via 1,3,5-

tris(4-nitrophenyl)-1,3,5-triazinane-2,4,6-trione (1-NO₂): Following the

general procedure with 4-nitrophenylisocyanate (1.3 g, 7.9 mmol) and

CsF (24 mg, 0.16 mmol). After filtration, 1-NO₂was obtained as a yellow

solid (1.2 g). This crude material was used as follows: A solution of calci-

um chloride (1 g, excess) in water (20 mL) was added to 1-NO₂and zinc

dust (5 g, excess) in ethanol (100 mL). This mixture was heated to reflux

for 3 h, cooled to room temperature, and filtered on a fritted funnel. The

filtrate was extracted with CH₂Cl₂, washed with water, and dried over

MgSO₄. After filtration and evaporation to dryness, the crude product

was purified by column chromatography on silica gel with ethyl acetate

132.5, 128.7, 126.0, 112.2, 109.8, 92.7, 86.9, 40.6 ppm; IR (KBr): n˜ =2207

ꢀ1

ꢅ

(C C, m), 1776 (C=O, vw), 1719 cm (C=O, s); Raman: n˜ =2208 (C C,

m), 1776 cm^ꢀ1(C=O, vw); HRMS: (EI) m/z calcd for C₅₁H₄₃N₆O₃:

787.3396 [M+H]⁺; found: 787.3382; elemental analysis calcd (%) for

C₅₁H₄₂N₆O₃: C 77.84, H 5.38, N 10.68; found: C 77.27, H 5.48, N 10.07.

1,3,5-Tris(4-{[4-(diphenylamino)phenyl]ethynyl}phenyl)-1,3,5-triazinane-

2,4,6-trione (2-NPh₂): Following the general procedure with 1-Br

(500 mg, 0.84 mmol), CuI (32 mg, 0.16 mmol), [PdCl₂ACHTUNTRGENUNG(PPh₃)₂] (60 mg,

0.08 mmol), DMF (20 mL), Et₃N (5 mL), and 4-ethynyl-N,N-diphenylani-

line (1.13 g, 4.2 mmol). The product was purified by column chromatog-

raphy with ethyl acetate/hexane 1:4 (600 mg, 61%). ¹H NMR (200 MHz,

CDCl₃, TMS): d=7.67 (d, ³J_H,H=8.2 Hz, 6H), 7.43–7.29 (m, 24H), 7.18–

7.03 ppm (m, 24H); ¹³C{¹H} NMR (50 MHz, CDCl₃, TMS): d=148.7,

147.5, 133.1, 132.7, 129.8, 128.8, 125.5, 124.1, 122.5, 115.8, 91.7, 88.0 ppm

1

to give a gray solid, which required oven drying (660 mg, 62%). H NMR

(200 MHz, CD₃SOCD₃, TMS): d=7.00 (d, ³J_H,H=8.4 Hz, 6H), 6.58 (d,

³J_H,H=8.4 Hz, 6H), 5.28 ppm (s, 6H); ¹³C{¹H} NMR (50 MHz,

CD₃SOCD₃, TMS): d=150.5, 149.6, 129.9, 123.9, 114.3 ppm; IR (KBr):

n˜ =3461, 3379 (NH, m), 1762 (C=O, vw), 1683 cm^ꢀ1(C=O, vs); Raman:

n˜ =3068 (NH, m), 1767 cm^ꢀ1(C=O, s); MS (EI): m/z calcd for

C₂₁H₁₉N₆O₃: 403.1518 [M+H]⁺; found: 403.1515; elemental analysis

calcd (%) for C₂₁H₁₈N₆O₃: C 62.68, H 4.51, N 20.88; found: C 62.54, H

4.52, N 20.26.

ꢅ

(three overlapped peaks); IR (KBr): n˜ =2209 (C C, m), 1772 (C=O, vw),

ꢀ1

1718 cm^ꢀ1(C=O, s); Raman: n˜ =2216 (C C, m), 1777 cm (C=O, vw);

ꢅ

Sonogashira coupling reaction – general procedure: In an oven-dried

Schlenk tube, an excess of the alkyne (5 or 6 equiv) was added to a mix-

HRMS (EI): m/z calcd for C₈₁H₅₄N₆O₃: 1158.4257 [M]⁺; found:

ture of 1-Br (1 equiv), CuI (20 mol%), and [PdCl

G

1158.4235.

DMF and Et₃N. After 2 days of stirring at 708C and cooling to room tem-

perature, the solvents were removed by cryoscopic transfer. The reaction

mixture was extracted with CH₂Cl₂, washed with water, and dried over

MgSO₄. After filtration and evaporation to dryness, the crude product

was purified by column chromatography on silica gel.

1,3,5-Tris{4-[(ferrocenyl)ethynyl]phenyl}-1,3,5-triazinane-2,4,6-trione (5):

Following the general procedure with 1-Br (668 mg, 1.12 mmol), CuI

(43 mg, 0.22 mmol), [PdCl₂ACHTNUTRGNE(UGN PPh₃)₂] (79 mg, 0.11 mmol), DMF (20 mL),

Et₃N (5 mL), and ethynylferrocene (1.18 g, 5.6 mmol). The product was

purified by column chromatography with CH₂Cl₂(460 mg, 42%).

¹H NMR (200 MHz, CDCl₃, TMS): d=7.64 (d, ³J_H,H=8.4 Hz, 6H), 7.39

(d, ³J_H,H=8.4 Hz, 6H), 4.55 (s, 6H), 4.29 ppm (s, 21H); ¹³C{¹H} NMR

(50 MHz, CDCl₃, TMS): d=148.6, 132.7, 132.6, 128.8, 125.8, 90.7, 85.1,

1,3,5-Tris{4-[(4-methoxyphenyl)ethynyl]phenyl}-1,3,5-triazinane-2,4,6-

trione (2-OMe) from 1-Br: Following the general procedure with 1-Br

(594 mg, 1 mmol), CuI (38 mg, 0.2 mmol), [PdCl₂ACHTUNTRGENUNG(PPh₃)₂] (70 mg,

ꢅ

0.1 mmol), DMF (20 mL), Et₃N (5 mL), and 4-ethynylanisole (660 mg,

5 mmol). The product was purified by column chromatography eluting

with CH₂Cl₂(610 mg, 82%).¹H NMR (200 MHz, CDCl₃, TMS): d=7.67

71.9, 70.4, 69.4, 65.0 ppm; IR (KBr): n˜ =2205 (C C, m), 1777 (C=O, vw),

ꢀ1

1710 cm^ꢀ1(C=O, vs); Raman: n˜ =2207 (C C, vs), 1779 cm (C=O, w);

ꢅ

HRMS (EI): m/z calcd for C₅₇H₃₉Fe₃N₃O₃: 981.1039 [M]⁺; found:

3

(d, J_H,H=8.4 Hz, 6H), 7.52 (d, ³J_H,H=8.6 Hz, 6H), 7.41 (d, J_H,H=8.4 Hz,

6H), 6.92 (d, ³J_H,H=8.6 Hz, 6H), 3.87 ppm (s, 9H); ¹³C{¹H} NMR

(50 MHz, CDCl₃, TMS): d=160.3, 148.7, 133.6, 133.0, 132.8, 128.9, 125.5,

981.1023.

1,3,5-Tris{4-[(trimethylsilyl)ethynyl]phenyl}-1,3,5-triazinane-2,4,6-trione

(3-TMS): Following the general procedure with 1-Br (2 g, 3.37 mmol),

CuI (128 mg, 0.67 mmol), [PdCl₂ACHTNUGRTNEUNG(PPh₃)₂] (236 mg, 0.33 mmol), DMF

(50 mL), Et₃N (10 mL), and ethynyltrimethylsilane (2.9 mL, 20.2 mmol).

ꢅ

115.2, 114.4, 91.4, 87.5, 55.7 ppm; IR (KBr): n˜ =2216 (C C, m), 1778 (C=

ꢀ1

O, vw), 1718 cm^ꢀ1(C=O, s); Raman: n˜ =2219 (C C, m), 1778 cm (C=O,

ꢅ

vw); HRMS (EI): m/z calcd for C₄₈H₃₃N₃O₆K: 786.2006 [M+K]⁺; found:

786.2019; elemental analysis calcd (%) for C₄₈H₃₃N₃O₆: C 77.10, H 4.45,

N 5.62; found: C 77.16, H 4.47, N 5.57.

The product was purified by column chromatography with Et₂O/hexane

1:1 (1.37 g, 63%). ¹H NMR (200 MHz, CDCl₃, TMS): d=7.61 (d, J_H,H

=

3

8.4 Hz, 6H), 7.35 (d, ³J_H,H=8.4 Hz, 6H), 0.29 ppm (s, 27H);

2-OMe from 3-H (see later): In an oven-dried Schlenk tube, a solution of

¹³C{¹H} NMR (50 MHz, CDCl₃, TMS): d=148.5, 133.5, 133.3, 128.8,

ꢅ

3-H (150 mg, 0.35 mmol), CuI (5.3 mg, 0.028 mmol), [PdCl

(PPh₃)₂]

125.0, 104.1, 96.6, 0.31 ppm; IR (KBr): n˜ =2160 (C C, m), 1778 (C=O,

ꢀ1

(9.8 mg, 0.014 mmol), and 4-iodoanisole (262 mg, 1.12 mmol) in DMF

(20 mL) and Et₃N (5 mL) was stirred at 708C overnight. After cooling to

room temperature, the solvents were removed by cryoscopic transfer.

vw), 1711 cm^ꢀ1(C=O, vs); Raman: n˜ =2160 (C C, vs), 1781 cm (C=O,

ꢅ

w); UV/Vis (CH₂Cl₂): l_max(e) = 254 (84700), 264 (90100), 308 nm (sh,

710 mol^ꢀ1dm³cm^ꢀ1); HRMS (EI): m/z calcd for C₃₆H₃₉N₃O₃Si₃: 645.2299

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Linear and Nonlinear Optical Properties of Functionalized Isocyanurates

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[M]⁺; found: 645.2287; elemental analysis calcd (%) for

C₃₆H₃₉N₃O₃Si₃·C₄H₈O₂: C 65.45, H 6.45, N 5.72; found: C 65.23, H 6.63,

N 5.72.

(Chroma e650sp–2p) by a compact CCD spectrometer module BWTek

BTC112E. Total fluorescence intensities were obtained by integrating the

corrected emission spectra measured by this spectrometer. TPA cross sec-

tions s₂were determined from the TPEF cross sections s₂F and the fluo-

rescence quantum yield F. TPEF cross sections were measured relative

to fluorescein in 0.01m aqueous NaOH at l=715–980 nm,^[53–54]using the

appropriate solvent-related refractive index corrections.^[55]Data points

between l=700 and 715 nm were corrected according to reference [56].

The quadratic dependence of the fluorescence intensity on the excitation

power was checked for each sample and all the wavelengths, thus indicat-

ing that the measurements were carried out in intensity regimes at which

saturation or photodegradation did not occur.

1,3,5-Tris(4-ethynylphenyl)-1,3,5-triazinane-2,4,6-trione (3-H): In an

oven-dried Schlenk tube, a solution of 3-TMS (820 mg, 1.27 mmol) and

TBAF (0.38 mL, 1m, 0.38 mmol) in THF (30 mL) was shielded from light

and stirred overnight at room temperature. After evacuation of the sol-

vent, the reaction mixture was extracted with CH₂Cl₂, washed with water,

and dried over MgSO₄. After filtration and evaporation to dryness, the

crude product was purified by column chromatography on silica gel with

CH₂Cl₂(300 mg, 55%). ¹H NMR (200 MHz, CD₂Cl₂, TMS): d=7.69 (d,

³J_H,H=8.4 Hz, 6H), 7.42 (d, ³J_H,H=8.4 Hz, 6H), 3.29 ppm (s, 3H);

¹³C{¹H} NMR (50 MHz, CD₂Cl₂, TMS): d=148.5, 134.2, 133.5, 129.0,

Computational details: DFT calculations were run using the Gaussian09

package.^[57]The standard B3LYP/6–31G* level was retained for all this

study based on previous investigations.^[39]The reported vibrational fre-

quencies were corrected by using the appropriate scaling factors.^[58]In

this study, the polarizable continuum model (PCM),^[59]including the sol-

vent effect was chosen for the calculation in solution. For the analysis of

the molecular-orbital contribution to the electronic absorption bands of

the studied compounds, the time-dependent DFT (TDDFT) method was

employed and the DFT-optimized ground-state geometries were used.

Theoretical absorption spectra were plotted using SWizard,^[60]whereas

the molecular orbital (MO) analysis was carried out with the AOMix

program.^[61]DFT calculations were then used to compute the first-order

hyperpolarizabilities of selected molecules of this study (see the Support-

ing Information for more details).^[62,63]

ꢅ ꢀ

ꢅ

123.9, 82.5, 79.1 ppm; IR (KBr): n˜ =3275 ( C H, vs), 2110 (C C, w),

1774 (C=O, vw), 1705 cm^ꢀ1(C=O, vs); Raman: n˜ =2113 (C C, vs),

ꢅ

1774 cm^ꢀ1(C=O, w); UV/Vis (CH₂Cl₂): l_max(e)=251 (74300), 278 nm (sh,

3500 mol^ꢀ1dm³cm^ꢀ1); HRMS (EI): m/z calcd for C₂₇H₁₅N₃O₃: 429.1113

[M]⁺; found: 429.1105; crystals of X-ray quality were grown by slow dif-

fusion of pentane into a solution of 3-H in CH₂Cl₂.

Methyl 4-ethynylphenylcarbamate (4): In an oven-dried Schlenk tube, 3-

TMS (467 mg, 0.72 mmol) and potassium carbonate (331 mg, 2.4 mmol)

in THF (20 mL) and methanol (20 mL) was stirred at room temperature

for 4 h. After evacuation of the solvent, the reaction mixture was extract-

ed with CH₂Cl₂, washed with water, and dried over MgSO₄. After filtra-

tion and evaporation to dryness, the crude product was purified by

column chromatography on silica gel with hexane/Et₂O 1:1 (298 mg,

1

3

X-Ray crystallography: Diffraction data frames for 1-CN, 1-Br, 3-H, and

4 were collected on a APEXII, Bruker-AXS diffractometer using Mo_Ka

radiation (l=0.71073 ꢂ). The structures were solved by direct methods

with the SIR97 program,^[66]and then refined with full-matrix least-square

methods based on F²(SHELX-97)^[67]with the aid of the WINGX^[68]pro-

gram. The contribution of the disordered solvents to the calculated struc-

ture factors was estimated following the BYPASS algorithm,^[69]imple-

mented as the SQUEEZE option in PLATON.^[70]All the non-hydrogen

atoms were refined with anisotropic thermal parameters. Hydrogen

78%). H NMR (200 MHz, CDCl₃, TMS): d=7.48 (d, J_H,H=8.6 Hz, 2H),

7.38 (d, ³J_H,H=8.6 Hz, 2H), 6.75 (s, 1H), 3.82 (s, 3H), 3.07 ppm (s, 1H);

¹³C{¹H} NMR (50 MHz, CDCl₃, TMS): d=154.2, 138.8, 133.4, 118.6,

ꢅ ꢀ

117.2, 83.8, 77.0, 52.9 ppm; IR (KBr): n˜ =3330 (NH, vs), 3279 ( C H,

vs), 2107 (C C, m), 1714 cm^ꢀ1(C=O, vs); MS (EI): m/z calcd for

ꢅ

C₁₀H₉NO₂: 175.0633 [M]⁺; found: 175.0629; elemental analysis calcd for

C₁₀H₉NO₂: C 68.56, H 5.18, N 8.00; found: C 68.64, H 5.29, N 7.73; crys-

tals of X-ray quality were grown by slow diffusion of pentane into a solu-

tion of 4 in CH₂Cl₂.

Luminescence measurements: These

Table 6. Crystal data, data collection, and refinement parameters for 1-CN, 1-Br, and 3-H and 4.

measurements were performed on

dilute solutions contained in 1 cm

quartz cells (ca. 10^ꢀ6m, optical density

<0.1) at room temperature (208C)

with an Edinburgh Instruments

(FLS920) spectrometer equipped with

a 450 W Xenon lamp and a Peltier-

cooled Hamamatsu R928P photomul-

tiplier tube in photon-counting mode.

Fully corrected emission spectra were

obtained at l_exc=l^a_m^b_a^s_xwith an optical

density at l_excꢂ0.1 to minimize inter-

nal absorption. Luminescence quan-

tum yields were measured according

to reported procedures.^[52]

[a]

[b]

Compound

1-CN·C₅H₁₂

1-Br

3-H·CH₂Cl₂

4

formula

M_r

T [K]

crystal system

space group

a [ꢂ]

b [ꢂ]

c [ꢂ]

a [8]

b [8]

C₂₄H₁₂N₆O₃

432.40

150(2)

C₂₁H₁₂Br₃N₃O₃

594.07

100(2)

monoclinic

C2/c

22.1026(12)

8.3291(4)

24.4655(15)

90.0

115.842(2)

90.0

4053.6(4)

8

C₂₇H₁₅N₃O₃

429.42

100(2)

trigonal

R3c

13.5264(13)

13.526

24.608(2)

90.0

120.0

3899.2(5)

6

1.097

C₁₀H₉NO₂

175.18

100(2)

monoclinic

P21/a

9.6420(17)

9.5215(16)

10.8502(17)

90.0

115.989(8)

90.0

895.4(3)

4

orthorhombic

Pcab

12.2308(3)

17.8380(4)

20.9795(5)

90.0

4577.16(19)

8

1.255

g [8]

V [ꢂ^ꢀ3

]

Z

1_calcd[gcm^ꢀ3

]

1.947

1.300

TPA measurements: These measure-

ments were conducted by investigating

the two-photon excited fluorescence

(TPEF) of the fluorophores in CH₂Cl₂

at room temperature (10^ꢀ4m) accord-

ing to the experimental protocol estab-

lished by Xu and Webb.^[53]To span the

range of l=700–980 nm, a Nd:YLF-

pumped Ti:sapphire oscillator was

used to generate pulses of 150 fs at

a rate of 76 MHz. The excitation was

focused into the cuvette through a mi-

croscope objective (10ꢃ, numerical

aperture (NA)=0.25). The fluores-

cence was detected in epifluorescence

crystal size [mm]

0.49ꢃ0.29ꢃ0.24

1776

0.087

ꢀ15/15

ꢀ22/23

ꢀ27/27

26228

5200

0.0417

0.1145

0.0519

0.55ꢃ0.48ꢃ0.37

2304

6.001

ꢀ25/28

ꢀ10/10

ꢀ31/31

16577

4646

0.0331

0.0809

0.0441

0.25ꢃ0.23ꢃ0.15

1332

0.073

ꢀ16/17

ꢀ17/16

ꢀ25/31

7587

0.55ꢃ0.48ꢃ0.32

368

0.092

ꢀ12/12

ꢀ13/13

8995

2040

0.0369

0.0966

0.0392

FACTHNUTRGNE(UNG 000)

m [mm^ꢀ1

]

hkl

total reflections

unique reflections

final R

1002

0.0693

0.1716

0.0720

0.1732

1.162

R_w

R indices (all data)

R_w(all data)

S_w

0.1198

1.096

0.0862

1.021

0.0984

1.070

[a] The highly disordered pentane solvate was suppressed during the structural resolution of this compound by

using the SQUEEZE procedure. [b] The highly disordered dichloromethane solvate was suppressed during the

structural resolution of this compound by using the SQUEEZE procedure (see the Experimental Section).

mode through

a

dichroic mirror

(Chroma 675dcxru) and a barrier filter

Chem. Eur. J. 2012, 00, 0 – 0

ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

&

15

&

ÞÞ

These are not the final page numbers!

A. Boucekkine, M. Blanchard-Desce, F. Paul et al.

atoms were finally included in their calculated positions. A final refine-

ment on F²with the unique intensities and 298, 271, 100, or 122 parame-

ters, respectively, converged in each case for the observed reflections

with I>2s(I). The crystallographic data are given in Table 6.

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Received: February 14, 2012

Published online: && &&, 0000

Chem. Eur. J. 2012, 00, 0 – 0

ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

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A. Boucekkine, M. Blanchard-Desce, F. Paul et al.

Optical Properties

G. Argouarch, R. Veillard, T. Roisnel,

A. Amar, H. Meghezzi,

A. Boucekkine,* V. Hugues,

O. Mongin, M. Blanchard-Desce,*

F. Paul* ........................ &&&& — &&&&

Triaryl-1,3,5-triazinane-2,4,6-triones

(Isocyanurates) Peripherally Function-

alized by Donor Groups: Synthesis

and Study of Their Linear and

Outside influence: A series of isocya-

absorption). In addition to a good

activity/transparency tradeoff regard-

ing the hyperpolarizabilities of these

compounds, high two-photon absorp-

tion cross sections are demonstrated

for the extended arylamino cyclo-

nurates functionalized by donor arms

at the periphery reveal remarkable

nonlinear optical properties for octu-

polar derivatives with strong donor

groups (see scheme; OPA=one-

photon absorption, TPA=two-photon

Nonlinear Optical Properties

AHCTUNGTRENNtGUN rimers.

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18

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www.chemeurj.org

ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 0000, 00, 0 – 0

ÝÝ

These are not the final page numbers!

Article Doi

Triaryl-1,3,5-triazinane-2,4,6-triones (Isocyanurates) peripherally functionalized by donor groups: Synthesis and study of their linear and nonlinear optical properties

DOI: 10.1002/chem.201200484

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Article abstract of DOI:10.1002/chem.201200484

Full text of DOI:10.1002/chem.201200484

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