Effects of Fluorine Substitution on the Intermolecular Interactions, Energetics, and Packing Behavior of N-Benzyl Substituted Diketopyrrolopyrroles

Article abstract of DOI:10.1021/acs.cgd.6b00157

Rationalizing the effects of molecular substitution in π-conjugated organic materials arising from well-defined intermolecular interactions, which can influence the formation of predefined packing motifs and control the emergence of π-π stacking represent

Full text of DOI:10.1021/acs.cgd.6b00157

Subscriber access provided by UNIV OF CALIFORNIA SAN DIEGO LIBRARIES
Article
Effects of fluorine substitution on the intermolecular interactions, energetics
and packing behaviour of N-benzyl substituted diketopyrrolopyrroles
Jesus Calvo-Castro, Graeme Morris, Alan R. Kennedy, and Callum J. McHugh
Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b00157 • Publication Date (Web): 08 Mar 2016
Downloaded from http://pubs.acs.org on March 17, 2016
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Crystal Growth & Design is published by the American Chemical Society. 1155
Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 47
Crystal Growth & Design
1
2
3
4
5
Effects of fluorine substitution on the intermolecular interactions, energetics and packing
behaviour of Nꢀbenzyl substituted diketopyrrolopyrroles
6
7
Jesus Calvo-Castro,* c Graeme Morris, a Alan R. Kennedy, b and Callum J. McHugh*a
8
9
a School of Science and Sport, University of the West of Scotland, Paisley, PA1 2BE, UK.
b Department of Pure & Applied Chemistry, University of Strathclyde, Glasgow, G1 1XL, UK.
c School of Life and Medical Sciences, University of Hertfordshire, Hatfield, AL10 9AB, UK.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ABSTRACT: Four novel systematically fluorinated DPPs and their single crystal structures are reported.
Structures involving direct fluorination of the DPP core phenyl rings and Nꢀbenzyl groups, display
1ꢀdimentional πꢀπ stacking motifs; a characteristic of Nꢀbenzyl substitution, where long and short
molecular axis displacement is induced by isosteric substitution of phenylic hydrogen atoms for fluorine
atoms. This characteristic stacking behaviour is destroyed upon trifluoromethyl substitution at the para
position of the core phenyl rings, in one case affording a novel molecular conformation and πꢀπ dimer
pair exhibiting a higher intermolecular interaction energy than any other structurally analogous DPP
based system reported previously. This crystal structure also exhibits a unique orthogonal association of
the πꢀπ dimer pairs along the crystallographic a and b axes, resulting in the formation of a framework that
is characterised by wellꢀdefined channels perpetuating along the length of the crystallographic c axis. The
role of fluorine induced stabilisation and its impact on optoelectronic properties in these systems is
identified via analysis of computed intermolecular interactions for all the crystal extracted nearest
neighbour dimer pairs and their associated cropped equivalents. Our results clearly reinforce the positive
role of benzyl substitution in DPP crystal structures to enhance optoelectronic behaviour. More
importantly they demonstrate the significant impact small changes in molecular structure can have on the
solid state properties of this molecular motif, particularly when fluorination is involved.
Dr. C. J. McHugh*
University of the West of Scotland
School of Science and Sport
Paisley, UK
PA1 2BE
Tel: +44 (141) 848 3210
Email: callum.mchugh@uws.ac.uk
1
ACS Paragon Plus Environment

Crystal Growth & Design
Page 2 of 47
1
2
3
4
5
6
7
8
9
Effects of fluorine substitution on the intermolecular
interactions, energetics and packing behaviour of
Nꢀbenzyl substituted diketopyrrolopyrroles
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Jesus Calvo-Castro,* c Graeme Morris, a Alan R. Kennedy, b and Callum J. McHugh*a
a School of Science and Sport, University of the West of Scotland, Paisley, PA1 2BE, UK.
b Department of Pure & Applied Chemistry, University of Strathclyde, Glasgow, G1 1XL, UK.
c School of Life and Medical Sciences, University of Hertfordshire, Hatfield, AL10 9AB, UK.
*Corresponding authors: callum.mchugh@uws.ac.uk, j.calvoꢀcastro@herts.ac.uk
ABSTRACT: Rationalising the effects of molecular substitution in πꢀconjugated organic
materials arising from wellꢀdefined intermolecular interactions, which can influence the
formation of predefined packing motifs and control the emergence of πꢀπ stacking represents a
current challenge in supramolecular design. Significant effort is potentially required to manage
the impact on solid state packing behaviour in materials that have been molecularly tuned to
carry out specific photophysical and electrochemical functions. In this regard, fluorine
substitution in πꢀconjugated systems has seen a recent surge of interest, primarily aimed towards
2
ACS Paragon Plus Environment

Page 3 of 47
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
the development of materials with enhanced optical and optoelectronic behaviour. In light of this
interest, in the following study, we report the synthesis and single crystal structures from a series
of four novel and structurally related, symmetric, fluorinated Nꢀbenzyl substituted
diketopyrrolopyrroles (DPPs). Two of the investigated series exhibit slipped cofacial πꢀπ dimer
pairs, which are consistent with those reported by us previously in halogenated DPPs.
Significantly, this characteristic stacking motif of Nꢀbenzyl substituted DPPs can be carefully
modified via the replacement of hydrogen atoms with trifluoromethyl and isosteric fluorineꢀ
hydrogen substituents. In the case of trifluoromethyl substitution, we identify a previously
unobserved packing motif exhibiting a framework of wellꢀdefined channels propagating along
the length of the crystallographic cꢀaxis. In each of the reported systems all of the nearest
neighbour dimer pairs have been identified and their intermolecular interaction energies
computed by means of M06ꢀ2X density functional at 6ꢀ311G(d) level. Through a detailed
theoretical analysis involving the determination of cropped dimer energetics, organic fluorine is
shown to play an active role in the stabilisation of the crystal extracted dimer pairs through a
number of additive and weak CꢀFꢀꢀꢀH, CꢀFꢀꢀꢀπF and CꢀFꢀꢀꢀπ intermolecular contacts. Contrary to
recent reports, we demonstrate that substitution of hydrogen by fluorine can also lead to dramatic
changes in solid state packing behaviour as a consequence of these weak interactions. Given the
importance of organic fluorine substitution in the construction of πꢀconjugated materials for
optoelectronic materials we feel that this work should be of interest to the wider community
involved in supramolecular design of organic conjugated systems, and in particular to those
investigating organic fluorine as well as diketopyrrolopyrrole containing architectures.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3
ACS Paragon Plus Environment

Crystal Growth & Design
Page 4 of 47
1
2
3
4
INTRODUCTION
5
6
7
8
9
Historically, diketopyrrolopyrroles (DPPs) have been widely utilised in industry as high
performance pigments in view of their exceptional properties such as brightness as well as light
and weather fastness.1ꢀ5 More recently, DPP based technologies have emerged as promising
charge transfer mediating materials in optoelectronic devices such as organic light emitting
diodes, organic field effect transistors as well as in solar energy conversion technologies such as
dye sensitised solar cells and organic photovoltaics.6ꢀ17 We are currently engaged in the design of
novel crystalline and thin film DPP platforms18ꢀ20 with a view to developing an inꢀdepth
understanding of their crystallographic intermolecular interactions, aimed towards the rational
design of sensing applications18, where the signal transduction can be either optical or
optoelectronic. In this regard, small structural changes have been observed to exert dramatic
changes to intermonomer interactions and hence associated charge transfer properties,19ꢀ22 which
in Nꢀbenzyl substituted DPPs are related to characteristic slipped cofacial πꢀπ stacking dimer
pairs, closely aligned along their short molecular axes upon Nꢀsubstitution.19 Understanding the
role of functional groups and substituent effects in these systems, which can facilitate or disrupt
the formation of those desirable packing motifs, via wellꢀdefined interactions is crucially
important in supramolecular design. There remains an identified need for studies, such as the one
reported herein, where systematic substitutions are performed on a common core structure and
the effects of manipulating the crystal lattice and intermolecular packing interactions are
explored inꢀdepth. In this work, we focus our interests on the role of organic fluorine in
influencing the crystal structures and 1ꢀdimensional πꢀπ stacks in a series of Nꢀbenzyl substituted
DPPs. In recent years, studies involving the interactions of fluorine substituents have seen a
surge of interest, particularly in the fields of life sciences and solid state materials.23 Fluorine is
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
4
ACS Paragon Plus Environment

Page 5 of 47
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
often used in substitutions of hydrogen atoms given their similar polarizabilities; however, this
isosteric substitution is associated to a significant change in occupied volume. Upon substitution,
physical and chemical properties in these types of comparative systems are known to be
significantly affected given the different electronegativities of the atoms involved.23ꢀ25 As an
example, the electron density of a perfluorinated ring is reversed compared to that of its nonꢀ
fluorinated analogue. In crystalline environments, organic fluorine can participate in a series of
intermolecular interactions such as CꢀFꢀꢀꢀH, CꢀFꢀꢀꢀFꢀC, CꢀFꢀꢀꢀπF and πꢀπF.23ꢀ28 Despite its large
electronegativity however, organic fluorine rarely forms Hꢀbonding intermolecular interactions
and these are often restricted to specific cases when their formation involving much better
acceptor atoms such as oxygen and nitrogen are sterically hindered.24,25,29 Although normally
weak, these interactions can however induce significant structural changes in the solid state.23
Therefore, despite an increasing understanding of the role played by organic fluorine in
influencing intermolecular interactions and packing behaviour, additional studies addressing the
key role fluorine plays in crystal engineering are warranted. This is particularly appropriate in
the development of DPP based materials, where reports of fluorine substitution are limited and
have not involved an inꢀdepth and systematic crystallographic analysis.30ꢀ32
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Y
HFHBDPP (X = H, Y = F, Z = Bn)
HFFBDPP (X = H Y = F, Z = FBn)
THHBDPP (X = CF3, Y = H, Z = Bn)
THFBDPP (X = CF3, Y = H, Z = FBn)
Z
N
X
O
O
(i)
O
O
Y
(ii)
Y
O
O
N
Z
X
Y
Scheme 1. DPP synthetic route. (i) PhCNXY, Na, tꢀamyl alcohol, reflux; (ii) BnBr or
pentafluoroꢀBnBr, K2CO3, DMF, 120 °C;
5
ACS Paragon Plus Environment

Crystal Growth & Design
Page 6 of 47
1
2
3
4
5
6
7
8
9
To this end, we report the synthesis, determination and characterisation of a series of four
symmetric, fluorinated Nꢀbenzyl substituted DPP single crystal structures (Scheme 1). The four
structures, HFHBDPP, HFFBDPP, THHBDPP and THFBDPP were given names with a form
of XYZDPP arising from their topology (see Figure 1) where X and Y denote the substitution of
the para and meta positions of the phenyl rings attached to the central DPP core respectively. In
turn, Z represents isosteric substitution of the phenylic hydrogen atoms for fluorine atoms within
the benzyl groups.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. Illustration of long and short molecular axes of DPP based systems (left). Long and
short molecular axis view of πꢀπ dimer pairs of HFHBDPP (top) and HFFBDPP (bottom).
PhenylꢀDPP cores in short molecular axis view of HFFBDPP are highlighted for ease of
visualisation.
It is worthwhile to note that two of the structures reported herein; namely HFHBDPP and
HFFBDPP exhibit 1ꢀdimensional slipped cofacial πꢀπ stacks consistent with those reported by
us previously.19 This type of packing behaviour is often thought to represent a key structural
feature leading to the emergence of semiconductor bandwidths in organic crystalline
6
ACS Paragon Plus Environment

Page 7 of 47
Crystal Growth & Design
1
2
materials.19,21,22 The degree of long and short molecular axis slip is markedly different in both
structures, which we attribute to effects of DPP core phenyl versus benzyl fluorination. Thus,
HFHBDPP exhibits a cofacial arrangement of monomers in the πꢀπ stacks with a long molecular
axis slip (ꢁx) of 3.72 Å and short molecular axis slip (ꢁy) of 0.35 Å. This arrangement of
monomers is entirely consistent with the previously reported nonꢀfluorinated equivalent
(HHHBDPP) where ꢁx = 4.50 Å and ꢁy = 0.30 Å. In turn, additional fluorination of the benzyl
substituents affords an extreme slipped arrangement of monomers in the πꢀπ stacks with ꢁx and
ꢁy equal to 9.12 Å and 2.31 Å respectively. In this case, the structure deviates from our previous
halogenated series with an increase in the short molecular axis slip. It is therefore clearly
apparent in this system, that direct fluorination of the core phenyl and benzyl ring systems can
afford changes in crystal packing (and molecular conformation, vide infra) which may contribute
to a significant impact in both the predicted magnitude and sign of charge carriers (vide infra). In
contrast to direct fluorination, trifluoromethyl substitution on the para position of the phenyl
rings attached to the central DPP core is manifest in considerable disruption to the characteristic
slipped packing motif in both THHBDPP and THFBDPP. The latter structure in particular,
whereby the Nꢀbenzyl substituents were also fluorinated exhibits a highly unusual cofacial dimer
pair arrangement where the monomers are offset with respect to their short molecular axis by ca.
46°. An orthogonal arrangement of the repeating units produced by the dimer pairs in this
structure results in the formation of channels that perpetuate along the length of the
crystallographic c axis (vide infra). From a search of the Cambridge Structural Database (CSD)
this is the first reported DPP structure displaying this type of packing motif and as a result, is of
particular interest and will be extensively discussed herein.
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
7
ACS Paragon Plus Environment

Crystal Growth & Design
Page 8 of 47
1
2
3
4
5
6
7
8
9
In summary, given the current interest in fluorine based πꢀconjugated materials in optical and
optoelectronic applications and the key role played by crystal structure in defining the efficiency
and behaviour of solid state devices, we feel that this study should be of wide interest to those
engaged in the engineering of novel organic charge transfer mediating materials as well as to
those interested in developing an inꢀdepth understanding of intermolecular interactions in
πꢀconjugated systems, in particular involving organic fluorine.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
EXPERIMENTAL SECTION
Reagents and instrumentation. Unless otherwise specified, all starting materials and reagents
were purchased from Fisher Scientific, SigmaꢀAldrich or VWR and used as received without
1
13
further purification. H NMR and C NMR spectra were determined using a Bruker AV3 400
MHz spectrometer (in CDCl3) provided by the University of Strathclyde in Glasgow, UK.
Elemental analyses were carried out using the service provided by the University of Strathclyde
in Glasgow, UK. FTIR analyses were carried out on the neat samples by attenuated total
reflectance using a Thermo Scientific Nicolet iS5 FTIR Spectrometer, with an iD5 ATR
(Diamond) sampling accessory.
Synthesis. 3,6ꢀbis(3,5ꢀdifluorophenyl)ꢀ2,5ꢀdihydropyrrolo[3,4ꢀc]pyrroleꢀ1,4ꢀdione (HFDPP).
3,5ꢀdifluorobenzonitrile was added to a solution of sodium tꢀamyloxide, prepared by dissolving
sodium metal wire (0.91 g, 39.56 mmol) in anhydrous 2ꢀmethylꢀ2ꢀbutanol (30 mL), and the
resulting mixture heated to reflux. Under vigorous stirring, dimethyl succinate (1.11 g,
7.60 mmol) dissolved in anhydrous 2ꢀmethylꢀ2ꢀbutanol (18.5 mL) was added over 1.5 h. After
further stirring for 2 h at reflux temperature, the mixture was cooled to 60 °C and treated with
8
ACS Paragon Plus Environment

Page 9 of 47
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
methanol (15 mL) and hydrochloric acid (37 %, 10 mL). The precipitate was collected by
filtration, washed with water, methanol and dichloromethane and then dried to give HFHDPP
(1.55 g, 56.6 %) as a red powder. IR (ATR)/cm−1: 3151 (NH), 3083 (ArH), 3048 (ArH), 3021
(ArH), 1651 (C=O), 1592 (NH), 1581 (C=C), 1136 (CF), 734 (ArH). Anal. Calcd. for
C18H8F4N2O2: C, 60.01; H, 2.24; N, 7.78. Found: C, 57.78; H, 1.94; N, 7.10. Melting Point: >
400 °C.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3,6ꢀbis[4ꢀ(trifluoromethyl)phenyl]ꢀ2,5ꢀdihydropyrrolo[3,4ꢀc]pyrroleꢀ1,4ꢀdione (THDPP). As per
the method described for HFDPP using sodium metal wire (0.73 g, 31.74 mmol) in 2ꢀmethylꢀ2ꢀ
butanol (25 mL), 4ꢀ(trifluoromethyl)benzonitrile (2.53 g, 14.78 mmol) and dimethyl succinate
(0.92 g, 6.29 mmol) in 2ꢀmethylꢀ2ꢀbutanol (14.5 mL). The product THDPP (1.74 g, 65.2 %) was
obtained as a red powder. IR (ATR)/cm−1: 3142 (NH), 3082 (ArH), 3039 (ArH), 2984 (ArH),
1637 (C=O), 1600 (NH), 1586 (C=C), 1440 (C=C), 1315 (CꢀF), 679 (ArH). Anal. Calcd. for
C20H10F6N2O2: C, 56.61; H, 2.38; N, 6.60. Found: C, 53.37; H, 1.72; N, 6.18. Melting Point: >
400 °C.
2,5ꢀdibenzylꢀ3,6ꢀbis(3,5ꢀdifluorophenyl)pyrrolo[3,4ꢀc]pyrroleꢀ1,4ꢀdione
(HFHBDPP).
A
suspension of HFDPP (0.40 g, 1.11 mmol) and anhydrous K2CO3 (1.66 g, 12.01 mmol) in
°
anhydrous DMF (20 mL) was heated at 120 C under nitrogen atmosphere. At this temperature
and under vigorous stirring a benzyl bromide (1.87 ml, 11.00 mmol) solution in DMF (10 ml)
was added over 1 h. Stirring and heating at 120 °C were continued for 1 h and after cooling to
room temperature salt was filtered and washed with DMF. After precipitation with methanol the
crude product was purified by wet flash chromatography eluting with hexaneꢀdichloromethane
9
ACS Paragon Plus Environment

Crystal Growth & Design
Page 10 of 47
1
2
1
3
4
(7:3) to give HFHBDPP (0.11 g, 18.3 %) as a bright orange powder. H NMR (CDCl3): 5.00
5
6
13
(4H, s, CH2); 6.93ꢀ6.98 (2H, m, ArH), 7.18ꢀ7.20 (4H, m, ArH), 7.27ꢀ7.37 (10H, m ArH). C
7
8
9
NMR (CDCl3): 45.69, 106.77, 107.01, 107.26, 110.41, 111.98, 112.06, 112.18, 112.26, 126.62,
127.81, 129.01, 130.12, 130.17, 130.32, 136.61, 146.99, 161.66, 161.80, 162.03, 164.15, 164.30.
IR (ATR)/cm−1: 3074 (ArH), 3029 (ArH), 2920 (CH2), 1682 (C=O), 1582 (C=C), 1438 (CH2),
1385 (CH2), 1133 (CF), 737 (ArH). Anal. Calcd. for C32H20F4N2O2: C, 71.11; H, 3.73; N, 5.18.
Found: C, 71.39; H, 3.89; N, 5.13. TLC: Rf (dichloromethane) 0.42, (ethyl acetate) 0.77. Melting
Point: 222ꢀ224 °C
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2,5ꢀbis(pentafluorobenzyl)ꢀ3,6ꢀbis(3,5ꢀdifluorophenyl)pyrrolo[3,4ꢀc]pyrroleꢀ1,4ꢀdione
(HFFBDPP). As per the method described for HFHBDPP from HFDPP (0.72 g, 2.00 mmol),
anhydrous potassium carbonate (0.30 g, 2.17 mmol), anhydrous DMF (50 mL) and 2,3,4,5,6ꢀ
pentafluorobenzyl bromide (0.58 g, 2.22 mmol) dissolved in anhydrous DMF (30 mL).
Purification of the crude product by wet flash column chromatography eluting with hexaneꢀ
dichloromethane (1:1) followed by precipitation with methanol gave HFFBDPP (0.045 g, 5.62
1
%) as a bright yellow powder. H NMR (CDCl3): 5.05 (4H, s, CH2), 6.98ꢀ7.03 (2H, m, ArH)
13
7.22ꢀ7.25 (4H, m, ArH). C NMR (CDCl3): 34.42, 107.05, 107.29, 107.57, 109.19, 109.29,
110.44, 111.58, 111.85, 129.48, 129.57, 129.66, 136.27, 138.69, 139.86, 142.34, 143.83, 146.13,
146.31, 160.99, 161.74, 161.91, 164.24, 164.36. IR (ATR)/cm−1: 3093 (ArH), 3057 (ArH), 2960
(CH2), 2921 (CH2), 1695 (C=O), 1589 (C=C), 1502 (C=C), 1436 (CH2), 1386 (CH2), 1125 (CF),
694 (ArH). Anal. Calcd. for C32H10F14N2O2: C, 53.35; H, 1.40; N, 3.89. Found: C, 53.27; H,
0.98; N, 3.76. TLC: Rf (dichloromethane) 0.50, (ethyl acetate) 0.75. Melting Point: 268ꢀ270 °C
10
ACS Paragon Plus Environment

Page 11 of 47
Crystal Growth & Design
1
2
3
4
2,5ꢀdibenzylꢀ3,6ꢀbis[4ꢀ(trifluoromethyl)phenyl]pyrrolo[3,4ꢀc]pyrroleꢀ1,4ꢀdione
(THHBDPP).
5
6
7
8
As per the method described for HFHBDPP from THDPP (0.60 g, 1.41 mmol), anhydrous
potassium carbonate (2.17 g, 15.70 mmol), anhydrous DMF (25 mL) and benzyl bromide (2.43
g, 14.29 mmol). After precipitation with methanol, purification of the crude product by wet flash
column chromatography eluting with hexaneꢀdichloromethane (1:1) gave THHBDPP (0.21 g,
24.7% yield) as a bright yellow powder. 1H NMR (CDCl3): 4.99 (4H, s, CH2), 7.19ꢀ7.21 (4H, m,
ArH), 7.27ꢀ7.36 (6H, m, ArH), 7.72 (4H, d, ArH), 7.88 (4H, d, ArH). 13C NMR (CDCl3): 45.69,
110.57, 122.15, 124.85, 125.88, 126.60, 127.73, 128.98, 129.38, 130.94, 132.44, 132.77, 133.11,
133.42, 136.85, 147.97, 162.37. IR (ATR)/cm−1: 3081 (ArCH), 3034 (ArCH), 2940 (CH2), 1678
(C=O), 1609 (C=C), 1437 (C=C), 1409 (CH2), 1377 (CH2), 1321 (CF), 1106 (CF), 1069 (CF),
667 (ArCH). Anal. Calcd. for C34H22F6N2O2: C, 67.55; H, 3.67; N, 4.63. Found: C, 67.10; H,
3.32; N, 4.59. TLC: Rf (dichloromethane) 0.54, (ethyl acetate) 0.79. Melting Point: 262ꢀ264 °C
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2,5ꢀbis(pentafluorobenzyl)ꢀ3,6ꢀbis[4ꢀ(trifluoromethyl)phenyl]pyrrolo[3,4ꢀc]pyrroleꢀ1,4ꢀdione
(THFBDPP). As per the method described for HFHBDPP from THDPP (0.85 g, 2.00 mmol),
anhydrous potassium carbonate (0.30 g, 2.17 mmol), anhydrous DMF (50 mL) and 2,3,4,5,6ꢀ
pentafluorobenzyl bromide (0.50 g, 1.92 mmol) dissolved in anhydrous DMF (30 mL).
Purification of the crude product by wet flash column chromatography eluting with hexaneꢀ
dichloromethane (3:2) and precipitation with methanol gave THFBDPP as a bright yellow
1
13
powder (0.122 g, 16.24%). H NMR (CDCl3): 5.04 (4H, s, CH2), 7.80 (8H, m, ArH). C NMR
(CDCl3): 34.39, 109.25, 110.51, 119.27, 121.99, 124.69, 126.13, 128.92, 130.45, 132.74, 133.08,
133.42, 133.72, 136.11, 138.63, 139.82, 142.36, 143.83, 146.31, 147.14, 161.32. IR (ATR)/cm−1:
2944 (CH2), 1679 (C=O), 1609 (C=C), 1499 (C=C), 1418 (CH2), 1376 (CH2), 1328 (CF), 1127
11
ACS Paragon Plus Environment

Crystal Growth & Design
Page 12 of 47
1
2
3
4
5
6
7
8
9
(CF), 1114 (CF), 1066 (CF), 669 (ArH). Anal. Calcd. for C34H12F16N2O2: C, 52.06; H, 1.54; N,
3.57. Found: C, 52.18; H, 1.05; N, 3.57. TLC: Rf (dichloromethane) 0.63, (ethyl acetate) 0.83.
Melting Point: 281ꢀ283 °C
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Preparation of Crystals for Single Crystal XꢀRay Diffraction analysis. All of the crystals
were obtained from DCM/hexane (1:1) by slow evaporation of a cooled solution.
Crystal structure determination. All measurements were made with Oxford Diffraction
instruments. Refinement was to convergence against F2 and used all unique reflections.
Programs used were from the SHELX suite.33 Hydrogen atoms were placed in idealized positions
and refined in riding modes. The CF3 group of THFBDPP was modelled as disordered over two
sites with occupancies refined to 0.595(4) and 0.405(4). These disordered groups required
restraints and constraints to be applied to displacement parameters. Selected crystallographic and
refinement parameters are given in Table 1. CCDC reference numbers 1449852ꢀ1449855 contain
the supplementary crystallographic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Table 1. Selected crystallographic data and refinement parameters for XYZBDPP compounds
Compound
Formula
HFHBDPP
HFFBDPP
THHBDPP
THFBDPP
C32H20F4N2O2 C32H10F14N2O2 C34H22F6N2O2 C34H12F16N2O2
Mr (g molꢀ1)
Crystal system
Space group
540.50
monoclinic
P21/c
720.42
monoclinic
P21/c
604.53
monoclinic
P21/c
784.46
tetragonal
Pꢀ4b2
12
ACS Paragon Plus Environment

Page 13 of 47
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
123(2)
123(2)
9.1947(4)
9.8373(4)
15.3292(6)
91.889(4)
1385.79(10)
2
123(2)
15.2024(18)
9.3312(11)
9.8704(11)
104.458(11)
1355.8(3)
2
123(2)
Temperature (K)
a (Å)
5.6106(3)
24.1920(15)
8.8718(5)
91.853(5)
1203.55(12)
2
18.5781(3)
18.5781(3)
9.2249(2)
b (Å)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
c (Å)
β (°)
V/Å3
3183.94(10)
4
Z
1.5418
1.5418
0.71073
6287
1.5418
11986
3134
Wavelength (Å)
Measured reflections
Unique reflections
Rint
4660
9895
2340
2757
3165
0.0274
0.0330
0.0453
0.0279
2765
2013
2599
2405
Observed rflns [I >
2σ(I)]
ꢁ (mmꢀ1)
0.970
181
1.560
226
0.121
199
1.506
257
No. of parameters
2θmax (°)
146.52
0.0449
0.1292
1.046
146.36
0.0443
0.1286
1.075
53.98
146.22
0.0452
0.1279
1.047
0.0571
0.1441
1.045
R [on F, obs rflns only]
wR [on F2, all data]
GoF
0.421/ꢀ0.251
0.508/ꢀ0.421
0.341/ꢀ0.196
Largest diff.
peak/hole/e Åꢀ3
0.281/−0.238
13
ACS Paragon Plus Environment

Crystal Growth & Design
Page 14 of 47
1
2
3
4
5
6
7
8
9
Computational details. All molecular modelling studies were carried out using the density
functionals indicated below as implemented in Spartan10 software.34 Dimer interaction energies,
ꢁECP, were all corrected for Basis Set Superposition Error (BSSE) using the counterpoise
correction method of Boys and Bernardi.35 Using a cutꢀoff distance of van der Waals (VdW)
radius + 0.3Å, all nearest neighbour dimer interaction energies of crystal extractedꢀdimer
structures were calculated using the M06ꢀ2X density functional36 and triple zeta 6ꢀ311G(d) basis
set. This density functional has been shown to give good account of the dimer interaction
energies of πꢀπ interacting systems.37,38 All results in the main text therefore refer to
M06ꢀ2X/6ꢀ311G(d) calculations on crystal derived dimer species.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
RESULTS AND DISCUSSION
Structural description. It has previously been shown19 that in the solid state the unsubstituted
parent molecule HHHBDPP and its 4ꢀhalogenated derivatives XHHBDPP (X = Cl, Br, I and
B = benzyl) form a structural series. All of these molecules are crystallographically
centrosymmetric and have conformations with the rings of the benzyl substituents mutually anti
with respect to the DPP plane. They all adopt structures bases on slipped cofacial πꢀπ dimer pairs
of molecules. Moreover, there is a systematic variation in these interactions with increasing size
of X leading to increasing amounts of slip along the long molecular axis. This means that for
X = H and Cl (β form) the closest πꢀπ contacts are between the DPP units and the C6H4X rings
whilst for the more slipped X = Br and I the closest πꢀπ contacts are between pairs of C6H4X
rings, see Figures 1a and 1b. In all four cases the individual πꢀπ dimer pairs stack to give infinite
1ꢀdimensional constructs in which the individual DPP rings are parallel to one another.
14
ACS Paragon Plus Environment

Page 15 of 47
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. Dimeric contacts in (a) HHHBDPP top and (b) BrHHBDPP bottom. In both cases
1ꢀ dimensional stacks are formed form the individual cofacial πꢀπ dimers, but the degree of slip
differs such that in (a) the closest contacts are between the DPP and phenyl rings but in (b) the
closest contacts are between pairs of C6H4Br rings.19
The fluorinated species described here do not all conform to this structural type. HFHBDPP,
HFFBDPP and THHBDPP do have similar centrosymmetric molecular structures (Z’ = 0.5)
with anti conformations of the benzyl or CH2C6F5 groups. However, THFBDPP adopts an
15
ACS Paragon Plus Environment

Crystal Growth & Design
Page 16 of 47
1
2
3
4
5
6
7
8
9
entirely different molecular conformation. Again Z’ = 0.5 but here this is due to a twoꢀfold
rotation axis passing through the centre of the DPP group and perpendicular to the DPP plane.
This gives a syn arrangement of the CH2C6F5 substituents and this appears to sterically prevent
one side of the DPP plane from forming close πꢀπ contacts, see below.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Like the earlier reported XHHBDPP species, HFHBDPP and HFFBDPP do form
intermolecular one dimensional polymers that are propagated by πꢀπ contacts. Indeed
HFHBDPP has a structure closely related to those of the XHHBDPP species. Like them, it
forms a similar 1ꢀdimensional stack with close contacts between the halogenated aryl ring and
the DPP core. Here the stacks lie parallel to the crystallographic a axis. Further analysis does
though show some differences in the details of how these stacks are formed. Rather than short
C…C contacts as seen with XHHBDPP, the shortest interactions with respect to van der Waals
distances are now F…C contacts (3.052(2) Å) with the shortest C…C contacts being slightly
longer than the sum of van de Waals distances (3.414(2) Å). To enable the short F…C contact,
the plane of the fluorinated ring is much more twisted with respect to the plane of the rings of the
DPP core (39.93(13) °) than in more planar XHHBDPP structures, compare Figure 3 with
Figure 2a. The shortest C…C πꢀπ contacts in HFHBDPP actually occur between its halogenated
aromatic rings (shortest C…C 3.294(2) Å) rather than in the DPP/aryl stack. As can be seen in
Figure 4, these contacts supported by C=O…H interactions, also give a polymeric 1ꢀdimensional
motif that cross links the earlier described stacks.
16
ACS Paragon Plus Environment

Page 17 of 47
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. Dimeric interactions in HFHBDPP showing the close contacts between F and the
DPP ring core. These interactions propagate to give a 1ꢀdimensional stack parallel to the a axis.
Figure 4. Interactions between pairs of C6H3F2 rings give a second 1 dimensional construct
based on πꢀπ interactions in HFHBDPP.
17
ACS Paragon Plus Environment

Crystal Growth & Design
Page 18 of 47
1
2
3
4
5
6
7
8
9
HFFBDPP forms no πꢀπ contacts shorter than the sum of van der Waals radii. Despite that, a
stack of molecules somewhat similar to those seen for XHHBDPP (X = Br, I) and HFHBDPP is
present. The dimer pair that forms the basis of these stacks is shown in Figure 5. Here
neighbouring molecules have parallel C6H3F2 rings but these are separated by distances longer
than those usually considered significant (closest C…C contact 3.845(3) Å). This dimeric
interaction may be supported by O…F and H…F interactions (3.017(2) and 2.61 Å respectively).
Thus, this species may be described with the same slipped πꢀπ stacked terminology and notation
as used previously, but it should be noted that it presents an extreme form of this geometry. With
respect to the sum of van der Waals radii, the shortest intermolecular distances in HFFBDPP are
F…F and F…C contacts (closest contacts F…C 2.791(2) Å, F…F 2.8282(16) Å). Although the
DPP core is involved here, the edgeꢀtoꢀface geometry of the contacts (see Figure 6) means that
these are not cofacial πꢀπ stacks.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
18
ACS Paragon Plus Environment

Page 19 of 47
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
Figure 5. The πꢀπ dimer that forms the basis of the 1 dimensional stack that propagates along the
b direction and which is used to describe the structure and properties of HFFBDPP. Compare
this to Figure 2b.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 6. Part of the structure of HFFBDPP showing the F…F and F…C contacts that are the
shortest contacts in this structure with respect to van der Waals distances.
The packing structures of the two CF3 containing species cannot be described using the same
stack of cofacial πꢀπ dimer description employed for the previously discussed structures. Unlike
any of the previously described species, THHBDPP forms πꢀπ contacts not through interactions
between its DPP and/or halogenated rings but instead through interactions of these groups with
the ring of the benzyl group, see Figure 7. (Closest face to face benzyl to DPP contact is C…C
3.329(3) Å; benzyl to C6H4CF3 contact is in edge to face mode through a CꢀH group of the
C6H4CF3 ring). Supported by C=O…H interactions this does form a 1ꢀdimensional
19
ACS Paragon Plus Environment

Crystal Growth & Design
Page 20 of 47
1
2
3
4
5
6
intermolecular polymer, but it is very different in its construction from the slipped cofacial πꢀπ
stacks of XHHBDPP and HFHBDPP.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
For THFBDPP, with the unusual syn geometry of its CH2C6F5 groups, close face to face πꢀπ
contacts between adjacent DPP moieties do occur (shortest contact distances C…C 3.405(4) Å
and N…C 3.208(3) Å) and give the dimeric units shown in Figure 8. However, due to the syn
conformation of the molecules these do not stack to give polymeric features. Neighbouring
dimers interact through F…C and F…F short contacts to give the packing structure shown in
Figure 10 (note that this leaves void regions in the structure). These channels run parallel to the
crystallographic c axis with a width (F…F) of approximately 6 Å.
Figure 7. In the structure of THHBDPP the πꢀπ contacts are based around interactions with the
benzyl groups. This is in contrast to all the other structures described here and in reference 19.
20
ACS Paragon Plus Environment

Page 21 of 47
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 8. Face to face, DPP to DPP dimer formed by THFBDPP. Note the unusual syn
conformation of the molecules.
Intermolecular interaction energies, ꢂECP. Organic fluorine has been extensively reported to
exhibit different types of intermolecular interactions such as CꢀFꢀꢀꢀH, CꢀFꢀꢀꢀFꢀC, CꢀFꢀꢀꢀπF and
πꢀπF. Although normally weak, these interactions can induce significant structural changes in
crystalline environments23 and as a consequence can play an active role in determining the solid
state properties of organic optoelectronic materials. To further investigate the role of fluorine
substitution in controlling and modifying the crystal structure and associated nearest
neighbouring intermolecular interactions of the fluorinated Nꢀbenzyl substituted DPP materials
reported herein, we computed ꢁECP for their extracted crystalline dimer pairs following the
method previously described for the XHHBDPP series.19,20 All of the nearest neighbour dimer
pairs within a cutꢀoff distance of that of van der Waals radius + 0.3 Å were identified from the
single crystal structures (SI1) of THHBDPP (10 neighbours), THFBDPP (8 neighbours),
HFHBDPP (10 neighbours) and HFFBDPP (12 neighbours) and their intermolecular
21
ACS Paragon Plus Environment

Crystal Growth & Design
Page 22 of 47
1
2
3
4
5
6
7
8
9
interactions, ꢁECP computed. In characterisation of the extracted dimer pairs , it is worthwhile to
reꢀemphasis that in this case the DPPꢀbased systems bearing trifluoromethyl substituents do not
exhibit the distinctive slipped cofacial πꢀπ dimer pairs observed previously with Nꢀbenzyl
substituted DPPs.18,19
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 9. Dimer pair (II) of THFBDPP showing the 46° offset of their short molecular axes with
respect to the centre of symmetry of the monomers.
Accordingly, the dimer pair (II) of THFBDPP was observed to exhibit a novel cofacial πꢀπ
stacking assembly (see Figures 9 and 10), with an intermonomer distance along the z axis of
3.36 Å. The crystallographic packing motif of THFBDPP, does not exhibit the typical slipped
cofacial stacking arrangement observed for other Nꢀbenzyl substituted diketopyrrolopyrroles.19
In this case, the structure displays an alternating series of the cofacial πꢀπ dimer pairs that are
orthogonal to one another and which extend along the a and b crystallographic axes. This
22
ACS Paragon Plus Environment

Page 23 of 47
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
crystallographic framework leads to the emergence of channels along the length of the
crystallographic c axis, with diffraction experiments confirming the absence of solvent in the
void space. A section of these channels is illustrated in Figure 10, where the structure is observed
to crudely adopt the form of an irregular octagon (with two different side lengths of ca 2.86 and
2.70 Å, inner angles of ca 40 and 50° and outer angles of ca 130 and 140°, unlike those of 45°
and 135° respectively for a regular octagon) with a measured crossꢀsectional surface area of ca
40.50 Å2. In this system, the short molecular axes of the monomers in the dimer pair are offset
by 46° with respect to one another, as illustrated in Figure 9. Favourable attractive intermolecular
interactions, as extracted from the large computed ꢁECP of ꢀ127.55 kJ molꢀ1 were observed,
which greatly exceed those computed for the analogous, nonꢀfluorinated Nꢀbenzyl substituted
DPP systems (ꢁECP = ꢀ70.20 and ꢀ69.90 kJ molꢀ1 for HHHBDPP and ClHHBDPPβ
respectively19). Thus, we propose significantly greater dimer thermal integrity should be
anticipated for the dimer pair of THFBDPP, along with the potential for unique optical,
electronic and adsorption behaviour.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
23
ACS Paragon Plus Environment

Crystal Growth & Design
Page 24 of 47
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 10. Capped stick illustration of the packing motif of THFBDPP as viewed along the
crystallographic c axis.
The reported DPP systems bearing direct DPP core phenyl and benzyl fluorination, HFHBDPP
and HFFBDPP, exhibit characteristic18,19 πꢀπ stacking dimer pairs (see Figure 1) which
propagate along their a and b crystallographic axes respectively. These πꢀπ dimer pairs display
intermonomeric displacements associated with ꢁx, ꢁy and ꢁz of 3.72, 0.35, 3.90 and 9.12, 2.31
and 3.59 Å for HFHBDPP and HFFBDPP respectively. The role of Nꢀbenzyl substitution in
precluding any significant intermonomeric displacement along the short molecular axis in
HFHBDPP is notable in a structure which also exhibits a small displacement along the long
molecular axis. This is in close agreement with the global minimum (ca 3.50 Å) of our
previously reported model systems for nonꢀsubstituted DPP analogues,19 and supports our
assertion that Nꢀbenzyl substitution in DPPꢀbased systems is associated to the preclusion of
24
ACS Paragon Plus Environment

Page 25 of 47
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
significant displacements along the short molecular axis in these crystal structures, thereby
favouring a slipped πꢀπ stacking configuration and maximising potential wavefunction
overlap.18,19 This is in distinct contrast to the substantial short molecular axes shifts and
herringbone packing arrangements exhibited by DPP pigments,39ꢀ41 nonꢀsubstituted acenes and
thiophenes.21,42ꢀ44 For the closely aligned πꢀπ dimer pair of HFHBDPP (ꢁx = 3.72 Å) an
intermolecular interaction energy of ꢀ71.02 kJ molꢀ1 was computed, which is comparable to
analogous Nꢀbenzyl diketopyrrolopyrroles (vide supra) and represents an almost twoꢀfold
increase in energy compared to the cofacial πꢀπ dimer pair of rubrene, (ꢁECP = ꢀ35.60 kJ molꢀ1
computed using the same density functional and basis set) which is widely employed as a charge
transfer mediating material.45ꢀ47 This clearly indicates for HFHBDPP, a great thermal integrity
of the slipped cofacial πꢀπ stacking dimer arrangement compared with rubrene. Large
intermolecular interactions and associated thermal integrities play a crucial role in precluding
small intermonomer displacements, which given the computed sensitivity of charge transfer
integrals to small intermonomer shifts19,21,22,48 represent a very desirable property in organic
charge transfer mediating materials. Closer inspection of the structure from the nonꢀfluorinated
HHHBDPP equivalent reported previously,19 reveals a number of subtle differences in
intermolecular interactions that emerge as a consequence of DPP core phenyl fluorination. Both
HHHBDPP and HFHBDPP display slipped πꢀπ structures with comparable long and short
molecular axes displacements (ꢁx = 4.50 Å and ꢁy = 0.30 Å for HHHBDPP and ꢁx = 3.72 Å
and ꢁy = 0.35 Å for HFHBDPP). As a result, both of the structures display very similar πꢀπ
stacking intermolecular interaction energies (ꢀ70.20 kJ molꢀ1 and ꢀ71.02 kJ molꢀ1 for HHHBDPP
and HFHBDPP respectively). However, it is notable that the melting points of both single
crystals are markedly different (278 °C and 222ꢀ224 °C for HHHBDPP and HFHBDPP
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
25
ACS Paragon Plus Environment

Crystal Growth & Design
Page 26 of 47
1
2
3
4
5
6
7
8
9
respectively), which is crudely reflected in their total intermolecular interaction energies
(ꢁECP = ꢀ294 kJmolꢀ1 and ꢀ247 kJmolꢀ1 for HHHBDPP and HFHBDPP respectively).
Differences in the overall interaction energies are consistent with the number of monomer
nearest neighbours in each system with the 12 neighbours observed in the structure of
HHHBDPP being reduced to only 10 in HFHBDPP. Thus, despite a similarity in πꢀπ stacking
energies, it is apparent that fluorination of the DPP core phenyl rings in HFHBDPP has a
negative impact on the overall crystal thermal stability compared to the nonꢀfluorinated
equivalent HHHBDPP.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
For HFFBDPP, the lower computed intermolecular interaction energy (ꢀ22.46 kJ molꢀ1) for the
πꢀπ stacking dimer pair can be readily understood on the basis of the associated intermonomer
displacements (9.12, 2.31 and 3.59 Å for ꢁx, ꢁy and ꢁz respectively) upon fluorination of the
benzyl groups. Whereas similar shifts along the long molecular axis have been previously
observed for Nꢀbenzyl substituted DPPs,19 the positive effect of the benzyl groups in precluding
significant displacements along the long molecular axis and hence enhancing spatial
intermonomer overlap was diminished upon isosteric substitution of the phenylic hydrogen
atoms of the benzyl substituents. In light of this effect and considering the impact of CF3
substitution observed in the structures of THHBDPP and THFBDPP we dedicate the remainder
of the paper to the computation and analysis of the intermolecular interactions, ꢁECP for all the
nearest neighbours of the systems reported in an effort to broaden our understanding of
fluorineꢀled interactions and their role in defining crystal packing motifs in Nꢀbenzyl substituted
DPPs.
26
ACS Paragon Plus Environment

Page 27 of 47
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 11. Capped stick illustration of the different nearest neighbour dimers of HFHBDPP.
27
ACS Paragon Plus Environment

Crystal Growth & Design
Page 28 of 47
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 12. Capped stick illustration of the different nearest neighbour dimers of HFFBDPP.
Figures 11 and 12 illustrate all of the identified nearest neighbour dimer pairs for HFHBDPP
and HFFBDPP respectively from which intermolecular interactions were computed. The
individual and simultaneous roles of benzyl/Zbenzyl (B) and Y substitution were investigated
through a series of systematically cropped dimer pairs, consistent with our previously reported
method.19,20 In short, the benzyl groups (either fluorinated or nonꢀfluorinated) and metaꢀfluoro
substituents on the DPP core phenyl rings were cropped and substituted with hydrogen atoms;
individually and then simultaneously, resulting in YDPP, BDPP and DPP structures respectively
with YBDPP representing the uncropped dimer pairs. Tables 2 and 3 summarise the computed
intermolecular interactions for the cropped and uncropped (structurally modified and nonꢀ
28
ACS Paragon Plus Environment

Page 29 of 47
Crystal Growth & Design
1
2
3
4
5
6
structurally modified) dimer pairs for the nearest neighbour dimer pairs of HFHBDPP and
HFFBDPPP respectively.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 2. Counterpoise corrected intermolecular interactions energies, ꢁECP for structurally
modified and nonꢀstructurally modified dimer pairs of all the nearest neighbours of HFHBDPP.
M06ꢀ2X/6ꢀ311G(d)
ꢂECP / KJ molꢀ1
Dimer pair
YBDPP
ꢀ5.36
YDPP
ꢀ6.77
BDPP
ꢀ0.84
DPP
ꢀ0.51
ꢀ28.68
0.38
I
II
ꢀ25.77
ꢀ1.56
ꢀ27.94
0.05
ꢀ27.91
ꢀ1.35
III
ꢀ71.02
ꢀ19.75
ꢀ30.96
ꢀ0.36
ꢀ76.17
ꢀ17.90
ꢀ36.37
0.22
IV (πꢀπ)
V
29
ACS Paragon Plus Environment