Name: Ms. Sanchari Debnath

Title: Dissipative Mechanisms in Organic Light-emitting Diodes: Role of Intramolecular Charge Transfer and Delayed Fluorescence 

Ph. D. Supervisor: Prof. Satish Patil

Date &Time : Wednesday, 31st January 2024 at 4.00 P.M.   

Venue: A-104 Lecture Hall, Chemical Sciences Building  

Organic light-emitting diodes (OLEDs) are emerging to replace conventional lighting technology due to their flexible device structures, multicolour emission, and ease of fabrication.[1] However, one of the key challenges in developing efficient emitters for OLEDs is overcoming the dissipative channel of triplet excitons.[2] A common approach to mitigate this challenge is to employ emitter molecules optimized for either thermally activated delayed fluorescence (TADF) or triplet-triplet annihilation (TTA) to enhance the external quantum efficiency (EQE).[3,4] Another alternative strategy to improve the quantum efficiency is deploying TADF chromophores with fluorescence emitters by recycling dark triplet excitons in a process, namely hyperfluorescence, which also retains narrow emission bandwidth.[5] Therefore, understanding the intricate photophysics of donor-acceptor (D-A) chromophores by exploiting the intramolecular charge transfer (ICT) state to unravel their multifarious applications attracts widespread attention.

In my thesis, I have rationally designed a series of aromatic imide-based D-A chromophores that display the TADF and TTA phenomenon, where the suitable choice of donor or acceptor governs the dominant delayed emission pathways by manipulating ICT state.[6] Further, by combining a TADF chromophore with a series of diketopyrrolopyrrole-based fluorescence emitters, efficient energy transfer could be facilitated, thereby enhancing the emission intensity of the fluorescence emitters. Nevertheless, in the quest to design new D-A chromophores, I made a serendipitous observation of stable radical cation formation in carbazole-based diketopyrrolopyrrole derivatives, which offers a plethora of promising applications.[7] Our in-depth photophysical studies provide insights into the importance of developing new chromophores, which offer myriad applications in optoelectronics.
[1] Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.; Bradley, D. D. C.; Santos, D. A. D.; Brédas, J. L.; Lögdlund, M.; Salaneck, W. R. Electroluminescence in Conjugated Polymers. Nature 1999, 397, 121– 128.
[2] Wong, M. Y.; Zysman-Colman, E. Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes. Adv. Mater. 2017, 29, 1605444.
[3] Uoyama, H.; Goushi, K.; Shizu, K.; Nomura, H.; Adachi, C. Highly Efficient Organic Light-emitting Diodes from Delayed Fluorescence. Nature 2012, 492, 234– 238.
[4] Dias, F. B.; Bourdakos, K. N.; Jankus, V.; Moss, K. C.; Kamtekar, K. T.; Bhalla, V.; Santos, J.; Bryce, M. R.; Monkman, A. P. Triplet Harvesting with 100% Efficiency by Way of Thermally Activated Delayed Fluorescence in Charge Transfer OLED Emitters. Adv. Mater. 2013, 25, 3707– 3714.
[5] Nakanotani, H.; Higuchi, T.; Furukawa, T.; Masui, K.; Morimoto, K.; Numata, M.; Tanaka, H.; Sagara, Y.; Yasuda, T.; Adachi, C. High-efficiency Organic Light-Emitting Diodes with Fluorescent Emitters. Nat. Commun. 2014, 5, 4016.
[6] Debnath et al. Modulation of Delayed Fluorescence Pathways via Rational Molecular Engineering. (Under revision)
[7] Debnath et al. Enhanced Chemical Stability of Radical Cations in Carbazole-based Diketopyrrolopyrrole Derivatives. (Manuscript under review)