1. Kaushik Balakrishnan, PhD
Research Summary
1 kaushik.balakrishnan@gmail.com
Dimension and size control self-assembly of functional
organic building blocks: New possibilities in organic
materials and device technologies
“0 D” “1 D” “2 D” “3 D”
FROM MOLECULES TO MATERIALS
• Synthesis: π-rich molecules (PDI, and BTDs) and macrocycles
• Self-assembly: Size and Dimension control
• Applications: Sensing, Optical, Energy and Display
2. Kaushik Balakrishnan, PhD
Research Summary
2 kaushik.balakrishnan@gmail.com
Self-Assembly
• Spontaneous organization of a component (building blocks) into
ordered structures using interactions (non-covalent, ionic, etc.) inherent
of the component(s) in select environment (solvent, vapor, surface, etc.).
• The self-assembled structures possess unique properties (new function)
specific to the nature of organization of the building blocks and are often
distinctly different from those of the individual building blocks.
• The collective organization of the building blocks therefore allow for
realizing structures larger than themselves - bottom-up construction tool.
• Ability to control dimension (0D, 1D, 2D, and 3D) and
size of resulting structures.
Examples of self-assembly
DNA structure, formation of crystals, etc.
100#nm#1#nm# 10#nm# 1#µm#1#Å#
Size of building blocks
(e.g., molecules, polymers
To#exploit#this#concept#for#material#science,#it#is#important#to#
understand#the#interac5ons#between#the#building#blocks.
Different#noncovalent#interac5ons#between#the#
molecules#play#significant#roles#during#the#self@
assembly#@#enabling#size#and#shape#control.#
Principles of Self-assembly
• Like prefers like
• Governed by energetically favorable interactions
4. Kaushik Balakrishnan, PhD
Research Summary
4 kaushik.balakrishnan@gmail.com
Self-Assembly of PTCDI*
PTCDI’s#exhibit#unusual#proper5es#like#
•#High'absorbi9viy'and'fluorescence'yields''
•'Thermal,'chemical'and'photochemical'stability'
•'Solvatochromism'strongly'observed'in'these'dyes''
•'Strong'tendency'to'aggregate'via'πAstacking'between'the'perylene'units'
•'nAtype'semiconductor'characteris9cs'as'compared'to'more'common'pAtype'
•'Synthe9c'advances'allow'func9onaliza9on'of'such'molecules'at'both'imide'nodes'(NAposi9ons)'and'
also'at'each'of'the'8Abay'func9onaliza9onA'leading'to'structural'diversity'A'structurally'these'dyes'
can'be'rigid#planar'to'unusually#twisted##
•'Func9onaliza9on'also'influences'the'solubility
*PTCDI = 3,4,9,10-Perylene Tetracarboxylic Diimide
N N
O O
OO
R R
Chemical Structure of PTCDI
Hadicke,)Acta)Cryst.)1986,)C42,)189;)195)
Klebe,)Acta)Cryst.)1989,)B45,)69.)
Wurthner,)Chem.)Eur.)J.)2007,)13,)450)–)465
π@stacking#distance#(d)#
0.335#(graphite)#–#0.43#(distorted)#nm#
Generally,#most#π@interac5ons#result
in#d@spacing#around#0.38#nm#
Highly efficient molecular stacking
Such ideal stacking is difficult to achieve because
of side-chains association and energy balance by
optimizing the lateral, and transverse offset
1D- assembly
Pathway for rapid change movement
5. Kaushik Balakrishnan, PhD
Research Summary
5 kaushik.balakrishnan@gmail.com
Self-Assembly of PTCDI
Propoxyethyl-PTCDI (PE-PTCDI)
Time dependence (methanol)
Balakrishnan)et)al.,)JACS,)2005,)pp10496
A
Molecular behavior
- well defined absorption
- - Fluorescence
Aggregation behavior
- Formation of crystals phase
- Quenching of free molecule emission
High solubility in chloroform with short side-chains
for PE-PTCDI
6. Kaushik Balakrishnan, PhD
Research Summary
6 kaushik.balakrishnan@gmail.com
Self-Assembly of PTCDI
Balakrishnan,+et+al.+JACS,+2006,+pp7390+25 µM Ethanolic solution
Side%chain*effect*
7. Kaushik Balakrishnan, PhD
Research Summary
7 kaushik.balakrishnan@gmail.com
Self-assembly: Toolkits for solution processing
A- Dispersion - Rapid approach injection of components into ‘poor’ solvents
B- Phase-transfer: Slow diffusion of molecules from ‘good’ to ‘poor’ solvents
C - Phase transfer at high temperature: Controlling the rate of diffusion by improving solubility
D- Gelation: Coercing components to maximize molecular interactions (useful in non-planar systems)
E - Vapor phase treatment: Another slow diffusion process to control size, and shape of assemblies
8. Kaushik Balakrishnan, PhD
Research Summary
8 kaushik.balakrishnan@gmail.com
Some more examples for Self-Assembly of PTCDI
Sayyad,)Balakrishnan)et)al.)manuscript)under)preparaJon
2D-assemblies
Controlling nature, and size of functionalization (i.e., side-chain) enables influencing
solubilities and using the solution processing toolkit allows for controlling size, and
shape of resulting assemblies. In turn this allows for fine tuning optical and electrical
characteristics.
Ultralong fluorescent wires
Balakrishnan)et)al.)manuscript)under)preparaJon
Tuning light emission
Under UV-light excitation
length of wires ~5 mm
Under ambient conditions
Balakrishnan,)et)al.)JACS,)2006,)pp7390
9. Kaushik Balakrishnan, PhD
Research Summary
9 kaushik.balakrishnan@gmail.com
Self-Assembly of Macromolecular Building Blocks
Arylene#Ethynylene#Macrocycles#(AEMs)#
•'Shape'persistent'πAsurface;'πArich'nonAcollapsible'core'(rigid);'Planar'(near'planar);'''
•'Large'area;''Pores'filled'with'ac9ve'func9onal'material.'(Hybrid'systems:'Applica9ons)
Highly'organized'
1D'assembly'
Hoger,)Chem.)Eur.)J.)2004,)10,)1320
For 1D nanostructure – Control lateral
association
J.S.Moore,Acc.Chem.Res,1997,402O413.
Nanofibers from a
tetracyclic non-planar
building block
Balakrishnan)et)al.,)J.)Am.)Chem.)Soc.;'2006;'pp6576'
Nanofibers from a
tetracyclic planar
building block
Such structures open new possibilities in
sensing applications (see slides on Applications of self-
assembles structures )
10. Kaushik Balakrishnan, PhD
Research Summary
10 kaushik.balakrishnan@gmail.com
Self-Assembly of Benzothiadiazole (BTD) Building Blocks
Balakrishnan)et)al.)Chem.)Commun.)2012,)pp11668
Ultra-long fluorescent micro-tube assembly
Planar yet flexible - how does this influence morphology?
11. Kaushik Balakrishnan, PhD
Research Summary
kaushik.balakrishnan@gmail.com
Applications: π-rich self-assembled structures
J.Am.Chem.Soc. 2007, pp7234
Influence of molecular ordering: Enhanced Electrical Properties
3-5x current flow upon doping
Doping of molecular wires
Influence of molecular ordering: Enhanced Sensing of Explosives
J.Am.Chem.Soc. 2007, pp6978
11
12. Kaushik Balakrishnan, PhD
Research Summary
kaushik.balakrishnan@gmail.com
Applications of π-rich self-assembled structures
Optical Waveguides Tunable Light Emission
HC
60
HC
60
UV-Photodetection System
OrganicSolarCells
Polarized Light Emission
Chem. Commun., 2012, pp11668
Chem. Commun., 2014, pp5600Chem. Commun., 2012, pp11668
J. Phys. Chem. B,, 2006, pp12327
Chem. Mater., 2009, pp2930
12
13. Kaushik Balakrishnan, PhD
Research Summary
kaushik.balakrishnan@gmail.com
Self-assembly: Dimension and size control from π-rich molecules
Solution Processing Toolkits
2D 3D micro-G
F
H I
Functional structures:
J.Am.Chem.Soc., 2005, pp10496
J.Am.Chem.Soc. 2006, pp7390
J.Am.Chem.Soc. 2006, pp6576
J.Am.Chem.Soc. 2007, pp6978
J.Am.Chem.Soc. 2007, pp7234
J. Phys. Chem. B,, 2006, pp12327
Nanoscale, 2011, pp3605
Chem. Commun., 2012, pp11668
Chem. Commun., 2014, pp5600
Chem. Commun., 2012, pp8904
Chem. Commun., 2013, pp684
Chem. Mater., 2009, pp2930
Unpublished results
13
✓Applica5ons#
✓'Op9cal'Sensing'
✓'Electrical'Response'
✓'OptoAelectronic'response'
✓'Tuning'absorp9on'
✓'Tuning'light'emission'and'bandAgap'
✓'Polarized'light'absorp9on'
and'emission'
✓'Molecular'materials'for'Display''
✓'Exploring'new'chemical'pathways'
from'selfAassembled'structures
Conclusions
• Morphology control via self-assembly can be an effective
approach to achieve new functional properties
• The advances in toolkits and synthetic advances to tailor make
desired structures are furthering the scope of applications
• Recent advances with co-assembled structures and post
chemical control over self-assembled structures are paving
new frontiers in materials science
• The chemical, physical, and structural diversity enable
addressing new challenges (see applications)
