Phenothiazine based π-conjugated molecule exhibiting mechanochromic properties Vivek Anand and R. Dhamodharan* Department of Chemistry, Indian Institute of Technology Madras email: damo@iitm.ac.in 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, 10052. 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