A tetrastable naphthalenediimide: Anion induced charge transfer, single and double electron transfer for combinational logic gates

Article abstract of DOI:10.1039/c3cc43280g

Herein we demonstrate the formation of the first tetrastable naphthalenediimide (NDI, 1a) molecule having multiple distinctly readable outputs. Differential response of 1a to fluoride anions induces intramolecular charge transfer (ICT), single/double electron transfer (SET/DET) leading to a set of combinational logic gates for the first time with a NDI moiety.

Full text of DOI:10.1039/c3cc43280g

Chemical Communications
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Volume 49 | Number 70 | 11 September 2013 | Pages 7671–7754
ISSN 1359-7345
COMMUNICATION
Pritam Mukhopadhyay et al.
A tetrastable naphthalenediimide: anion induced charge transfer, single and double
electron transfer for combinational logic gates

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A tetrastable naphthalenediimide: anion induced
charge transfer, single and double electron transfer for
combinational logic gates†
M. R. Ajayakumar,a Geeta Hundalb and Pritam Mukhopadhyay*a
Cite this: Chem. Commun., 2013,
49, 7684
Received 3rd May 2013,
Accepted 23rd May 2013
DOI: 10.1039/c3cc43280g
www.rsc.org/chemcomm
Herein we demonstrate the formation of the first tetrastable
naphthalenediimide (NDI, 1a) molecule having multiple distinctly
readable outputs. Differential response of 1a to fluoride anions
induces intramolecular charge transfer (ICT), single/double electron
transfer (SET/DET) leading to a set of combinational logic gates for
the first time with a NDI moiety.
All organic molecules that respond to stimuli and have the ability to
perform simple logic operations have found real-life applications in
medical diagnostics, physiological monitoring,1a–c etc.1 Presently, it
is anticipated that complex logic operations with multi-state redox
molecules2 can lead to miniaturised low power electronic devices.3
In this regard, the p-type organic materials with multiple oxidation
states have been in the forefront.4
Scheme 1 (a) Molecular structures of 1a–c. (b) An electronic device for anion
sensing with conductive radical anions of 1a.9a (c) Reduction potentials (vs. SCE)
of 1a–c. (d) Four states of 1a; neutral, deprotonated, radical anion and dianion.
In contrast, n-type organic materials have considerably lagged
behind in this area of frontier development. Naphthalenediimide
(NDI),5 a well-known n-type organic semiconductor with two reversible gates, like half-adders and 1 : 2 demultiplexers, for the first time with
redox states, can be an excellent candidate for the generation of a NDI moiety. Importantly, thermal ET processes have been applied
simple and complex logic gates.6 However, generation of combina- for the first time to achieve the 3-input AND gate and the 1 : 2
tional logic gates with NDI has remained elusive to date.7 Realization demultiplexer.
of multistable states with a suitably functionalized NDI moiety would
provide a platform to achieve this arduous task.
Anion sensing8 and its application in logic operations have
attracted tremendous interest. Recently, we9a and subsequently other
Herein, we have established for the first time the formation of a groups9b have demonstrated that specific anions can induce thermal
tetrastable NDI triggered by the differential stoichiometric response ET reactions in the NDI moiety having low-lying LUMO levels.9c The
of the NDI to fluoride anions (Scheme 1a and d). The light yellow resultant radical anions were highly conductive and could be applied
coloured neutral NDI solution transforms into a green or reddish in an electronic device (Scheme 1b).9a We have also recently shown
brown or a blue solution, as a result of the ICT or SET or DET that Cu(II)/Fe(III) can induce the formation of the radical cation in a
process, respectively. The neutral, deprotonated, radical anion and core-functionalized NDI with high-lying HOMO levels.10
the dianion states have distinct opto-electronic and magnetic
In this work, we have chosen three NDI derivatives (1a–c) (see
responses. We have applied the signature optical read-outs of these ESI†) having integrated hydrazimide unit(s) with or without the
states to realize a complex 3-input AND gate and combinational logic electron withdrawing (EW) CF3 group(s). The presence of p-orbital
wave functions at the N-positions in the diimide rings results in the
a Supramolecular and Material Chemistry Lab, School of Physical Sciences,
formation of node(s), which separates the NDI chromophore–
electrophore unit from the D–p–A hydrazimide chromophore
unit(s) (Scheme 1a).‡ We envisaged that this unique molecular
design can be utilized to generate distinct signal read-outs in the
electronic, optical and magnetic domains. Cyclic voltammetry (CV)
(Scheme 1c) and differential pulse voltammetry (DPV) experiments
with 1a–c in DMF (see ESI,† Fig. S1 and Table S1) clearly indicated
Jawaharlal Nehru University, New Delhi 110 06, India.
E-mail: m_pritam@mail.jnu.ac.in; Fax: +91-11-2674-2891; Tel: +91-11-2673-8772
b X-ray Crystallography: Prof. Geeta Hundal, Guru Nanak Dev University, Punjab,
India. E-mail: geetahundal@yahoo.com
† Electronic supplementary information (ESI) available. CCDC 936251. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c3cc43280g
c
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Fig. 1 (a) UV-vis-NIR absorption spectra of the four-states of 1a (3 Â 10À4 M). (i)
Addition of 15 equiv. of TBAF to 1a in dry DMF results in the formation of the ICT
state. (ii) 5 equiv. of TBAF with 1a in DMF gives persistent 1aꢀÀ. (iii) 1a gradually
transforms to its di-anionic state (1a2À) in DMF–H2O (99 : 1 v/v) with 30 equiv. of
TBAF. (b) Fluorescence spectrum of 1a2À [1a, 3 Â 10À5 M; lex, 607 nm].
Fig. 2 Crystal structure of 1a depicting the self-assembly due to N–HÁ Á ÁO
H-bonding along the c-axis. Solvents have been removed for clarity.
The ICT and SET states of 1a were found to be persistently stable for
several hours under ambient conditions. Notably, the dianion 1a2À was
also found to be stable under different conditions (Fig. 3a and b). For
instance, 1a2À generated in DMF–H2O (99 : 1 v/v) could be extracted in
CHCl3 and even washed with excess of water. The resultant pink
coloured solution shows absorptions at 397, 417, 545 and 582 nm.
Similarly, 1a2À could be extracted in Et2O from DMF–H2O (99:1 v/v)
with absorption bands at 393, 412, 550 and 592 nm. Thus, all the states
of 1a were found to be reasonably stable under ambient conditions.
Furthermore, we explored the compatibility and ease of blending
of some of the states in thin-films for possible applications on solid
surfaces. We could fabricate flexible and thin transparent films of
1aꢀÀ and 1a2À in polystyrene (PS). 1aꢀÀ was generated in DMF and
dried under vacuum. The brown powder obtained was mixed with
that 1a possessed the lowest first and second reduction potential
1
2
(ER and ER ) at À0.447 V and À0.920 V, respectively. The mono-
2
hydrazimide, 1c, shows the highest ER1 and ER .
1a in dry DMF undergoes deprotonation reactions at the hydra-
zimide NH positions in the presence of an excess of tetrabutyl-
ammonium fluoride (TBAF) to form an intense green coloured
solution. UV-vis spectroscopy revealed a characteristic broad ICT
band at 685 nm along with a strong UV absorption at 347 nm
(Fig. 1a). On the other hand, 1b being devoid of EW CF3 groups did
not undergo the ICT process even in large excess of TBAF (see ESI,†
Fig. S2 and S3). However, 1c could undergo facile deprotonation
under similar conditions (see ESI,† Fig. S4 and S5).
In contrast, 1a turned into a brown solution in the presence of only
5 equiv. of TBAF in DMF.11a UV-vis-NIR spectroscopy showed that the
parent p–p* transitions at 358 and 377 nm diminish with the
concomitant formation of a new set of bands at 472, 604, 645, and
774 nm (Fig. 1a). The signature absorption characteristics match with
that of the NDI radical anion and was ascribed to the doublet D0 -
Dn transitions. The SET reaction driven formation of 1aꢀÀ was further
confirmed using ESR spectroscopy with a strong signal at g = 2.0033
(see ESI,† Fig. S6). 1b and 1c underwent the SET reaction with TBAF
under similar conditions. As expected, with lower equivalents of TBAF,
the SET reaction is the preferred route over the deprotonation of 1a.
On the other hand, 1a gradually turned into a bluish solution in the
presence of a large excess of TBAF in DMF having a trace amount of
water.11b UV-vis spectroscopy revealed a new set of absorption bands at
397, 417, 550, and 600 nm (Fig. 1a), which excellently match with the
signature peaks of the reported dianion of NDI. The dianion 1a2À was
found to be diamagnetic in nature. Significantly, upon the DET reaction
the non-fluorescent 1a turned into a bright orange fluorescent solution
with a strong emission at 650 nm (Fig. 1b). However, 1b and 1c with a
À
PS in THF to obtain a flexible thin film of 1aꢀ (Fig. 3c). Similarly,
1a2À could also be embedded in PS to get a bluish-violet flexible
thin-film (Fig. 3d). UV-vis-NIR characterisation of the free-standing
thin films of 1aꢀÀ and 1a2À confirmed the stability of these reduced
species in the solid surface.
The establishment of four stable molecular states enabled the
generation of simple logic gates such as AND, XOR and INH in 1a
and combinational logics like a 3-input AND gate, a half-adder and
a 1 : 2 demultiplexer. For the demonstration of the 3-input AND
gate,13 non-degenerate stoichiometric amounts of 5 and 10 equiv.
of TBAF were taken as inputs In1 and In2, respectively, while H2O
was used as the third input, In3. The ON state was possible only
with the DET reaction (Fig. 4a). UV-vis-NIR spectroscopy confirmed
that 1a2À formed only with the addition of all the three channel
inputs. The characteristic signature peaks at 417 nm could be used
to achieve the 3-input AND gate.
Next, we realized a half-adder14 with 1a (Fig. 4b). Towards this,
10 equiv. of TBAF in DMF was chosen as chemically degenerate
2
significantly negative shifted ER did not undergo the DET reaction
under similar conditions (see ESI,† Fig. S7 and S8).
In effect, only 1a could form all the four distinct states. Therefore,
the distant EW CF3 groups in the hydrazimide Ph-rings of 1a play a key
role in lowering the LUMO levels and increasing the acidity of the NH
groups important for the ET reactions and the ICT states, respectively.
Crystal structure determination of 1a also highlighted the importance
of the NH groups towards self-assembly (Fig. 2). A ladder-like network
was formed as a result of a 10-membered N–HÁÁÁO H-bonding (N–O,
2.932(8) Å) between the imide carbonyl and the NH group of the
nearest NDI moieties (see ESI,† Fig. S9). It is important to note that
such close-packed structures in organic semiconductors are known to
generate large charge mobilities.12
Fig. 3 (a) Extraction of 1a2À into CHCl3 and Et2O from DMF–H2O and (b) the
corresponding absorption spectra. Free standing polystyrene thin-films
À
embedded with (c) 1aꢀ and (d) 1a2À [1a; 3 Â 10À4 M].
c
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Fig. 4 (a) Construction of a 3-input AND gate with the characteristic absorption spectra under the action of 3 inputs (In1–In3) with 1a. (b) A half-adder logic with two
inputs (In1 and In2). (c) A 1 : 2 demultiplexer circuit with the action of single input (In) and address input (A) with 1a. Truth tables of the respective complex logic gates
are also shown. All the spectra were recorded after providing sufficient equilibration time [1a, 3 Â 10À4 M].
reflections, 3964 independent (Rint = 0.0815), and 2163 observed reflec-
tions [I Z 2s(I)], 296 refined parameters, R = 0.13, wR2 = 0.34.
inputs In1 and In2. Molecule 1a responded to one of the inputs
by triggering the SET reaction, however, their combined action
triggered the deprotonation reaction. The AND and the INH
gates were realized through the formation of the ICT and the
radical anion states.
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Thus, the truth table for the half-adder was realized by green
and brown coloured states distinguishable by the naked eye or by
monitoring the multichannel signal read-outs at 347 or 645 nm (ICT)
and 472 or 774 nm (SET), which covered the UV-vis and the NIR range.
Finally, we could realize a 1 : 2 demultiplexer14,15 that processed
one data input, one address input and one output (Fig. 4c). We
applied 1a with TBAF (30 equiv.) as the input in DMF and H2O as the
address input (A). 1a with the TBAF input in DMF triggered the ICT
state leading to the recognition of the INH gate. Addition of water (A)
along with TBAF resulted in the DET reaction with signature bands
at 417, 561 or 603 nm conferring the AND gate. The interplay
between these green and blue coloured states and their multi-
channel signal read-outs in the UV-vis region led to the combina-
tional 1 : 2 demultiplexer logic circuit.
In summary, we have realized for the first time tetrastability in a
NDI molecule by combining deprotonation, SET and DET reactions.
A differential stoichiometric response of the neutral NDI molecule to
fluoride anions triggers the formation of the ICT, radical anion and
the dianion states. These states were found to have distinct RGB
colour codes distinguishable by the naked eye. We could realize a set
of combinational logic gates for the first time applying multichannel
signal read-outs of the thermal ET and ICT based reactions.
Furthermore, successful incorporation of the stable di-anion/radical
anion states into the free standing PS thin-films extends promise for
logic gate applications in solid-state devices. Our efforts are now
directed towards achieving complete reset ability in the NDI-based
molecules to realize molecular keypad based security devices.16
We thank DBT, DST and DST-PURSE for funding the research.
We thank the MALDI-TOF MS facility at CIF, SLS, JNU, FT-IR,
500 MHz NMR facility at AIRF, JNU. MRA thanks CSIR, India,
for research fellowship.
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Notes and references
‡ Crystal data for 1a: C28H14N4O4F6Á4C4H8O, M = 872.85, monoclinic,
g = 90.001, V = 2186.8(14) Å3, Z = 2, MoKa radiation (l = 0.71073 Å),
T = 100.0(2) K, m = 0.108 mmÀ1, Bruker APEX-II diffractometer, 14 031
P21/c, a = 12.939(5), b = 16.079(6), c = 10.585(4), a = 90.001, b = 96.796(11)1, 16 (a) F. Pu, Z. Liu, X. Yang, J. Ren and X. Qu, Chem. Commun., 2011,
47, 6024; (b) F. Pu, Z. Liu, J. Ren and X. Qu, Chem. Commun., 2011,
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c
7686 Chem. Commun., 2013, 49, 7684--7686
This journal is The Royal Society of Chemistry 2013