S. Ghosh, A. K. Banthia / Tetrahedron Letters 42 (2001) 501–503
503
The first order rate constant for this process (k=
6. Buffeteau, T.; Labarthet, F. L.; Pezolet, M.; Sourisseau,
C. Macromolecules 1998, 31, 7312–7320.
7. Tomalia, D. A.; Naylor, A. M.; Goddard, W. A. Angew.
Chem., Int. Ed. Engl. 1990, 29, 138–175.
8. Ameerunisha, S.; Zacharias, P. S. J. Chem. Soc., Perkin
Trans 2 1995, 1679–1682.
−
1
0
.00684 min ; t1/2=101 min) as determined from the
inset of Fig. 1, is similar in magnitude to that of other
1
1
azobenzenes. We have thus demonstrated the pho-
tochromic property is due to the isomerism of the
azobenzene moiety of dendrimer 1 on irradiation of 330
nm UV light. We anticipate that photoswitchable den-
drimers of this type will have applications in transport
systems based on the reversible perturbation of their
ability to encapsulate small molecules. Further studies
in our laboratory are in progress.
9. Selected data for dendritic wedge (1a): IR (KBr): 3375,
−
1 1
1732(s), 1644 cm ; H NMR (200 MHz, CDCl ) l: 6.2
3
(bs, 6H, all -CONH
6
-), 4.30(bs, 1H, -OH), 3.66 (s, 26H,
-CO CH , HO-CH
6
-), 3.29–3.27 (m, 12H, -CONH-CH2-
2
6
2
3
13
), 2.85–2.33 (m, 70H, all other -CH -); C NMR ( 50
2
MHz, CDCl ) l: 177.1 (NCꢀO; out), 174.1 (NCꢀO, in),
3
1
72.3 (CꢀO), 56.8, 56.1, 52.2, 51.2, 50.2, 49.9, 49.2, 45.1,
References
42.4, 37.7, 36.9, 32.5, 32. Anal. calcd for C H N O :
64 115 13 23
C, 53.58; H, 8.07; N, 12.69; found: C, 51.68; H, 7.79; N,
10.92.
1
2
3
. Zeng, F.; Zimmerman, S. C. Chem. Rev. 1997, 97, 1681–
712, and references cited therein.
. Junge, D. M.; McGrath, D. V. J. Am. Chem. Soc. 1999,
21, 4912–4913, and references cited therein.
1
10. Selected data for dendrimer (1): IR (KBr): 3315, 1722,
−
1 1
1632 cm ; H NMR (300 MHz, CDCl )l: 8.21 (d, 4H,
3
1
J=9 Hz), 8.0 (d, 4H, J=9 Hz), 6.21 (bs, 12H, -CONH-),
13
. Archut, A.; Vogtle, F.; De Cola, L.; Azzelini, G. C.;
3.68 (s, 52H), 3.11 (q, 24H), 2.81–2.39 (m, 140H);
C
Balzani, V.; Ramanujam, P. S.; Berg, R. H. Chem. Eur. J.
NMR (50 MHz, CDCl ) l: 173.0 (broad and unresolved,
3
1
998, 4, 699–706, and references cited therein.
-C6 ONH-, -C6 OOCH , - C6 OOCH -), 152.4 (ArC), 129.0
3 2
4
5
. Schenning, A. P. H. J.; Elissen-Roman, C.; Weener, J.
W.; Baars, M. W. P. L.; van der Gaast, S. J.; Meijer, E.
W. J. Am. Chem. Soc. 1998, 120, 8199–8208.
(ArC), 124.6 (ArCH), 121.5 (ArCH), 79.3, 75.1, 55.9,
53.0, 50.1, 49.0, 47.2, 46.5, 39.8, 36.9, 35.0, 32.5, 29.9.
Anal. calcd for C142H236N O : C, 54.95; H, 7.66; N,
28
48
. Zilker, S. J.; Bieringer, T.; Haarer, D.; Stein, R. S.; van
Egmond, J. W.; Kostromine, S. G. Adv. Mater. 1998, 10,
12.63; found: C, 52.79; H, 7.14; N, 11.21.
11. Shinkai, S.; Nakaji, T.; Nishida, Y.; Ogawa, T.; Manabe,
O. J. Am. Chem. Soc. 1980, 102, 5860–5865.
8
55–859.
.
.