Synthesis of the PDI Unit 6a (Donor)
Several methods have been reported for the monofunctionalization of PDI [6]
including one-pot imidization (route A) or a base-promoted coupling reaction
between naphthalene monoimide derivatives (route B) [7], as shown in Scheme 2.
We found the one-pot imidization reaction (route A) to be more practical than route
B: route B consisted of five steps and the open-form product 6b was labile under the
basic reaction conditions required to produce the closed product 6a. The one-pot
imidization, route A, was simple and 3 could easily be recovered via column
chromatography because the use of an excess amount of 3 was necessary. Concerning
the solubility and reactivity of perylene tetracarboxylic acid dianhydride (PDA) 4, the
imidization of 4 was, first, carried out with 2,6-diisopropylaniline (5) in imidazole;
then 3 in propionic acid solution was added to produce the closed product PDI 6a.
Synthesis of the TDI unit 13 (Acceptor)
The key concept for the synthesis of the TDI building block is the introduction of a
boronic ester group with a TDI moiety (compound 13) for the final coupling
reaction with PDI. Starting from N-(2,6-diisopropylphenyl)-9-(4,4,5,5-teramethyl1,3,2-dioxaborolan-2-yl)perylene-3,4-dicarboximide (10), building block 13 was
synthesized in the multistep sequence shown in Scheme 2 (steps d–f). For
the selective cross-coupling of boronic ester 10 with 4-bromonaphthalene1,8-dicarboxylic anhydride (8), the introduction of a bromo substituent at the
N-aryl group (i.e., 12) should come after the [Pd(PPh 3 ) 4 ]-catalyzed coupling
reaction (Scheme 2, step d). An excess amount of the naphthalene derivative
must be used during the coupling reaction (Scheme 2, step d) in order to favor
the hetero-coupling of 10 and 8 over the homo-coupling of 10. Next, the
monosubstitution (Scheme 2, step e) of 11 was accomplished by condensation of
the anhydride moiety with 4-bromo aniline in propionic acid. Compound 12 was
treated with bis(pinacolato)diboron to form its boronic ester derivative 13
(Scheme 2,step f).
Synthesis of the Linear Dyad 1
Finally, the open form of the dyad (dyad 1-a) was synthesized by Suzuki coupling
of the PDI part 6a and the TDI part 13 (Scheme 2, step g). The dyad 1-a was
obtained in 60% yield after gel permeation chromatography (GPC). Due to its
extended aromatic core, terrylene diimide shows a much lower solubility than its
smaller homologue perylene diimide. Concerning the poor solubility of the TDI
unit, the cyclization reaction was performed as the last step (Scheme 2, step h). As
shown in Fig. 2, the perylene part is susceptible to hydrolysis, so the cyclization had
to be performed rapidly (within 30 min). Cyclization using K 2 CO 3 as base in
ethanolamine completed the synthesis of the dyad 1. Besides unreacted 1-a, the
Optical Properties of Assemblies of Molecules and Nanoparticles
67
Several methods have been reported for the monofunctionalization of PDI [6]
including one-pot imidization (route A) or a base-promoted coupling reaction
between naphthalene monoimide derivatives (route B) [7], as shown in Scheme 2.
We found the one-pot imidization reaction (route A) to be more practical than route
B: route B consisted of five steps and the open-form product 6b was labile under the
basic reaction conditions required to produce the closed product 6a. The one-pot
imidization, route A, was simple and 3 could easily be recovered via column
chromatography because the use of an excess amount of 3 was necessary. Concerning
the solubility and reactivity of perylene tetracarboxylic acid dianhydride (PDA) 4, the
imidization of 4 was, first, carried out with 2,6-diisopropylaniline (5) in imidazole;
then 3 in propionic acid solution was added to produce the closed product PDI 6a.
Synthesis of the TDI unit 13 (Acceptor)
The key concept for the synthesis of the TDI building block is the introduction of a
boronic ester group with a TDI moiety (compound 13) for the final coupling
reaction with PDI. Starting from N-(2,6-diisopropylphenyl)-9-(4,4,5,5-teramethyl1,3,2-dioxaborolan-2-yl)perylene-3,4-dicarboximide (10), building block 13 was
synthesized in the multistep sequence shown in Scheme 2 (steps d–f). For
the selective cross-coupling of boronic ester 10 with 4-bromonaphthalene1,8-dicarboxylic anhydride (8), the introduction of a bromo substituent at the
N-aryl group (i.e., 12) should come after the [Pd(PPh 3 ) 4 ]-catalyzed coupling
reaction (Scheme 2, step d). An excess amount of the naphthalene derivative
must be used during the coupling reaction (Scheme 2, step d) in order to favor
the hetero-coupling of 10 and 8 over the homo-coupling of 10. Next, the
monosubstitution (Scheme 2, step e) of 11 was accomplished by condensation of
the anhydride moiety with 4-bromo aniline in propionic acid. Compound 12 was
treated with bis(pinacolato)diboron to form its boronic ester derivative 13
(Scheme 2,step f).
Synthesis of the Linear Dyad 1
Finally, the open form of the dyad (dyad 1-a) was synthesized by Suzuki coupling
of the PDI part 6a and the TDI part 13 (Scheme 2, step g). The dyad 1-a was
obtained in 60% yield after gel permeation chromatography (GPC). Due to its
extended aromatic core, terrylene diimide shows a much lower solubility than its
smaller homologue perylene diimide. Concerning the poor solubility of the TDI
unit, the cyclization reaction was performed as the last step (Scheme 2, step h). As
shown in Fig. 2, the perylene part is susceptible to hydrolysis, so the cyclization had
to be performed rapidly (within 30 min). Cyclization using K 2 CO 3 as base in
ethanolamine completed the synthesis of the dyad 1. Besides unreacted 1-a, the
Optical Properties of Assemblies of Molecules and Nanoparticles
67