1. Phenothiazine based π-conjugated molecule exhibiting mechanochromic properties
Vivek Anand and R. Dhamodharan*
Department of Chemistry, Indian Institute of Technology Madras
Introduction
Organic π-conjugated molecules have gained diverse applications in the fields of field-effect transistors, organic-light emitting diodes and organic solar cells.
Specifically, molecules having switchable solid-state emission owing to mechanical stimuli such as grinding, rubbing etc., are in high demand because of their promising
applications in mechanical sensors, security papers and optoelectronic devices.
The D-π-A type molecules exhibit distinct fluorescent properties owing to the intramolecular charge transfer (ICT) properties.
Mechanochromism
Compound 1 in solution under UV-lamp
Compound 1 in solid form under UV-lamp
Applying pressure by grinding
Synthetic Target
1H-NMR
Objectives of the Project 1
To synthesize phenothiazine and phenylene ethylene based organic luminogens
To Study their mechanochromic behaviour by (solid state) UV-Vis and fluorescence spectroscopy as well as by powder X-ray diffraction (PXRD) analysis
To study the donor-acceptor and ICT properties by photophysical methods
The rational behind choosing these moieties:
Non-planar puckered structure of phenothiazine along with excellent hole transporting properties very desirable for mechanochromic fluorescent materials.
Phenylene ethylene has rigid conjugated structure leading to high molar extinction coefficient and high fluorescence quantum yield
Decrease in intensity due to precipitation
Increase in intensity due to aggregation
Synthetic steps
Aggregation induced enhanced
emission studies
Increase in intensity till 40 % water fraction due
to aggregation and then gradual decrease
due to precipitation
Fig. 4: Fluorescence spectra (a) of compound 1 in different THF-water mixtures.
Fig. 3: Luminescence spectra (a), Photograph (b) and PXRD (c) of compound 1 upon different treatments
λmax = 538 nm
λmax = 547 nm
Before Grinding
After Grinding a b c
Study of Mechanochromic property
Vibronic coupling
Fig.1: UV-Visible (a) and Fluorescence (b) spectra of compound 1 in DCM, THF and toluene
π-π* transition
ICT transitions at λmax = 419 nm, 415 nm, 414 nm in DCM, toluene, THF
ICT Studies
ICT transition at
λmax = 537 nm, 520 nm, 515 nm in DCM, THF, toluene a b
References
Summary and Conclusion
Xue, P.; Yao, B.; Liu, X.; Sun, J.; Gong, P.; Zhang, Z.; Qian, C.; Zhang, Y.; Lu, R.; J. Mater. C, 2015, 3, 1018.
2. Nagai, A.; Okabe, Y.; Chem. Commun., 2014, 10,
3. Zhang, G.; Sun, J.; Xue, P.; Zhang, Z.; Gong, P.; Peng, J.; Lu, R.; J. Mater. C, 2015, 3,
2925.
We thank Department of Chemistry, IIT Madras for the infrastructure. Vivek Anand thanks IIT Madras for fellowship.
Novel compound 1 was designed and synthesized following the literature procedures and characterized by 1H and 13 C-NMR techniques.
Mechanochromic properties were studied using solid state fluorescence and PXRD.
3. The compound showed ICT peak owing to the D-π-A design and positive
solvatochromism.
4. The compound is found to show aggregate induced enhanced emission (AIEE) in
THF-water mixture.
5. The PLEDs fabrication and testing are currently under progress.
Acknowledgement