M. Brewis et al. / Tetrahedron Letters 42 (2001) 813–816
815
Table 1. The position of the primary absorption band (Q-band) of 4–9 in CH2Cl2 solution compared with that in EtOH
solution
Pc
4
5
6
7
8
9
umax (CH2Cl2)
umax (EtOH)
a705, 670
610
a705, 670
625
a705, 670
635
678
677
679
679
680
680
All concentrations were approximately equal (1×10−6 mol dm−3).
a Non-aggregated metal-free Pcs exhibit a split Q-band.
hulme Foundation for provision of a Research Fellow-
ship (N.B.M.).
References
1. Newcombe, G. R.; Moorefield, C. N.; Vo¨gtle, F. Den-
dritic Molecules: Concepts, Syntheses and Perspectives;
VCH: Weinheim, 1996.
2. Jin, R.-H.; Aida, T.; Inoue, S. J. Chem. Soc., Chem.
Commun. 1993, 1260–1262.
3. Dandliker, P. J.; Diederich, F.; Gross, M.; Knobler, C.
B.; Louati, A.; Sanford, E. M. Angew. Chem., Int. Ed.
Engl. 1994, 33, 1739–1741.
4. McKeown, N. B. Phthalocyanine Materials: Synthesis,
Structure and Function; Cambridge University Press:
Cambridge, 1998.
5. Pandey, R. K.; Herman, C. K. Chem. Ind. 1998, 739–744.
6. Brewis, M.; Clarkson, G. J.; Holder, A. M.; McKeown,
N. B. Chem. Commun. 1998, 969–970.
Figure 2. The Q-band absorption for (a) 4 in EtOH, (b,- - -)
6 in EtOH and (c) 6 in CH2Cl2.
7. Brewis, M.; Clarkson, G. J.; Goddard, V.; Helliwell, M.;
Holder, A. M.; McKeown, N. B. Angew. Chem., Int. Ed.
Engl. 1998, 37, 1092–1095.
8. Hawker, C. J.; Fre´chet, J. M. J. J. Am. Chem. Soc. 1990,
112, 7638–7647.
band in the UV–vis absorption spectra of 5 and 6
shows that self-association of the Pc cores is less preva-
lent than in 4 for EtOH solutions of similar concentra-
tion (Table 1). Nevertheless, the appearance of the
Q-band of 6 (Fig. 2) suggests that oligomeric molecular
aggregates are the majority species and that only a
small fraction of the Pc cores are isolated. Both 5 and
6 are isotropic liquids in the pure state and neither form
a lyotropic mesophase in concentrated EtOH solution.
It is apparent that peripheral substitution of Pc by four
non-ionic dendritic substituents is not an efficient
method of ensuring isolation in polar solvents. Similar
results have been obtained by other groups using den-
dritic substituents bearing ionic solubilising groups,
although the aggregation is reduced to some extent
presumably as a result of electrostatic repulsion.13,14 In
contrast to the behaviour of 4–6, UV–vis spectroscopy
of 7–9 shows that placing the dendritic substituents in
axial sites prevents aggregation in EtOH (Table 1).
Preliminary fluorescence studies of EtOH solutions of
7–9 reveal that excitation at 420 nm results in strong
fluorescence at 688 nm, whereas for ethanolic solutions
of 4–6 no significant fluorescence was observed.
9. Selected spectroscopic data for 4: u(CH2Cl2)/nm 705,
670, 65, 620, 422, 346; (KBr)/cm−1 3275 (NH), 2924,
2874, 1598; lH (CDCl3, 500 MHz, 50°C) −1.5 (2H, br s),
3.31–3.35 (24H, m), 3.49–3.53 (16H, m), 3.61–3.75
(48H, m), 3.86–3.90 (16H, m), 4.20–4.23 (16H, m), 5.45
(8H, br s), 6.57 (4H, br s), 6.92 (8H, br s), 7.66–7.73 (4H,
br m), 8.64–8.72 (4H, br m), 9.06–9.10 (4H, br m); m/z
(FAB) 2237, (M+). For 5: u(CH2Cl2)/nm 705, 670, 65,
620, 422, 346; (KBr)/cm−1 3275 (NH), 2924, 2874, 1598
lH (CDCl3, 500 MHz, 50°C) −0.5 (2H, br s), 3.31–3.36
(48H, m), 3.47–3.82 (160H, br m), 4.06–4.12 (32H, m),
5.00–5.05 (16H, br m), 5.49–5.55 (8H, br m), 6.41–6.45
(8H, br m), 6.52–6.64 (20H, br m), 6.95 (8H, br s),
7.76–7.83 (4H, br m), 8.93–9.03 (4H, br m), 9.31–9.41
(4H, br m); m/z (MALDI) 4384, (M+). For 6: u(CH2Cl2)/
nm 705, 670, 65, 620, 422, 346; (KBr)/cm−1 3275 (NH),
2924, 2874, 1598 lH (CDCl3, 500 MHz, 50°C) −0.42 (2H,
br s), 3.30–3.32 (96H, m), 3.44–3.80 (320H, br m),
3.96–4.07 (64H, m), 4.85–5.08 (48H, m), 5.54–5.56 (8H,
br m), 6.30–6.74 (76H, br m), 6.95–6.98 (8H, br m),
7.80–7.87 (4H, br m), 8.93–9.05 (4H, br m), 9.47–9.64
(4H, br m); m/z (MALDI) 8678, (M+). For 7: u(CH2Cl2)/
nm 678, 650, 610, 352; (KBr)/cm−1 2913, 2878, 1596; lH
(CDCl3, 500 MHz, 50°C) −0.78 (4H, s), 3.10 (8H, t), 3.33
(12H, s), 3.36 (4H, d), 3.40 (8H, t), 3.49 (8H, t), 3.65 (8H,
t), 3.56–3.59 (16H, m), 5.51 (2H, t), 8.29 (8H, m), 9.55
(8H, m); m/z (FAB) 1403, (M+). For 8: u(CH2Cl2)/nm
Acknowledgements
We thank EPSRC, Zeneca Specialities (now Avecia)
and BASF for financial support (M.B.) and the Lever-