reSeArCH Letter
The structure of fjord-type GNR 2 was carefully analysed by infrared
(IR), Raman, nuclear magnetic resonance (NMR), ultraviolet–visible
(UV-vis) absorption and emission spectroscopies to confirm the high
degree of regiocontrol during polymerization (Fig. 1f–h, section 12
in Supplementary Information; see Extended Data Figs. 2a, 3 for details
of the Raman and NMR spectroscopic analyses). After the initiation
reaction produces the first intermediate (1a in Fig. 1a), the subsequent
APEX reaction can in principle provide two possible regioisomeric
dimers (3a and 4a in Fig. 1f). Thus, we conducted step-by-step APEX
reactions to synthesize dimer 3a and model dimer 3b (Extended Data
Fig. 2b, c), which are more plausible products having [5]helicene moi-
eties, for reliable spectral comparisons. The stoichiometric APEX reac-
tion of I with model monomer M′ afforded tribenzochrysene (1b) in
91% yield, which is further π-extended with M′ to provide 3b in 86%
yield. In this reaction, the structural isomer 4b, which has sterically
congested [6]helicene moieties (which typically show upfield-shifted
hydrogen atoms on [6]helicene regions at 6–7 p.p.m. in^1 H NMR) was
not obtained at all (see^1 H NMR spectrum of 3b in Supplementary3,400 3,200 3,000
Wavelength (cm–1)1,6001,4001,2001,000 600800RRRRa2 : Mn = 32 kDa, = 1.212 : Mn = 13 kDa, = 1.232 : Mn = 150 kDa, = 1.214a (simulated)3a (observed)
3a (simulated)M/I10 : 1
50 : 1
100 : 1
300 : 1
500 : 1Mna
(kDa) ÐaÐÐÐ
Ð
Ð2.9
13
32
97
1501.25
1.23
1.21
1.22
1.22DPa,b7
34
83
253
391Yield
of 2 d75%
72%
85%
86%
82%Length
(nm)c3
15
36
109
169bInitiator
IMonomer
MInitial
intermediate
1aFjord-type GNR
2SiR+n-octylEtEt n–1R RRK regionR =Pd(OCOCF 3 ) 2
AgSbF 6
o-chloranil
ClCH 2 CH 2 Cl
80 °C, 12 hK region0204060801001201401600 100 200 300 400 500
M/I1.01.21.41.61.82.0c10 12 14 16 18 20 22
Retention time (min)Normalized intensityI/M =
1:500I/M =
1:300
I/M =
1:100I/M =
1:50I/M =
1:10d e
Mn (kDa) Mn (kDa)5101520253035020406080 100
Conversion (%)1.01.21.41.61.82.07917887877761,0751,0731,0721,0797898527691,081
8528498498491,076× 5× 5× 5× 5× 5× 5
773838× 1× 1× 1× 1× 1× 1f0.05.0× 1051.0× 1061.5× 1062.0× 106250 300 350 400 450 500 550 600
Wavelength (nm)Wavelength (nm)300 400 500 600 700 800Nomalized intensityMn = 2.9 kDa
(Ð = 1.25)Mn = 32 kDa
(Ð = 1.21)Mn = 13 kDa
(Ð = 1.23)Mn = 150 kDa^
(Ð = 1.22)Mn = 2.9 kDa (Ð = 1.25)
H(263 nm) = 1.9 × 105Mn = 32 kDa (Ð = 1.21)
H(262 nm) = 1.7 × 106Mn = 13 kDa (Ð = 1.23)
H(261 nm) = 7.4 × 105Mn = 150 kDa (Ð = 1.22)
H H(262 nm) = 1.9 × 106
(cm mol L–1)ghFig. 1 | APEX polymerization for structurally well defined GNRs.
a, Living APEX polymerization using phenanthrene (I) as the initiator
and benzonaphthosilole (M) as the monomer. Reaction conditions:
M (1.0 equiv.), Pd(OCOCF 3 ) 2 (1.0 equiv.), AgSbF 6 (2.0 equiv.),
o-chloranil (2.0 equiv.), ClCH 2 CH 2 Cl, 80 °C, 12 h. b, Table of results
of polymerization. I/M, molar ratio of I and M. aDetermined by using
PS standards. bCalculated using Mn. cEstimated length using the DP
value. Analyses of Mn and Đ were conducted with the crude product
of GNRs. dIsolated yield after purification by SEC. c, SEC charts of the
crude products of reactions with various M/I ratios. d, e, Mn and Mw
(Đ = Mw/Mn) profiles versus M/I and conversion of the monomer in the
living APEX polymerization. f, IR spectra of dimer 3a (black line) and
possible isomer 4a (blue line) predicted by density functional theory
(DFT) calculations at the B3LYP/6-31G(d) level, and observed IR spectra
of dimer 3a (purple line) and GNR 2 with different polymer lengths
(green, yellow and red lines). The IR spectra of 3a and various sizes of
GNR 2 support the formation of a fjord-type GNR structure (see section
12 in Supplementary Information for details). g, Absorption spectra of
GNR 2 with different polymer lengths. The molar absorptivity ε was
determined using the Mn values measured by SEC analyses.
h, Fluorescence spectra of GNR 2 with different polymer lengths.388 | NAtUre | VOL 571 | 18 JULY 2019