Title : Strategies for enhancement in light emission from fluorogenic molecules and semiconductor nanocrystals.
Speaker : Prof. Anindya Datta, IIT Bombay.
Date : 16/09/2021, 05:00 PM (Thursday), Online Mode.
Elucidation of ultrafast photo processes paves the way for engineering photoemission properties of molecules and materials that are not strongly emissive to start with.1 Fluorogenic molecules, which are not inherently fluorescent because of ultrafast nonradiative deactivation pathways associated with their flexible structure, have been rendered to be strongly fluorescent by complexation,2 crystallization,3,4 chemical modification5,6 and aggregation.7,8 The effect of each of these modifications has been studied using time resolved spectroscopy and hence, different parameters for engineering and finetuning their photophysical properties. Fluorescence lifetime imaging microscopy has yielded insight into development of fluorescent nano/microstructures of some of these molecules, with potential application in organic electronics7 and intracellular imaging.8
On a different note, photoluminescence (PL) of tetrapod shaped CdSe nanocrystals9–12 and spherical, aqueous CdS nanocrystals13,14 have been found to be governed by intricate exciton dynamics. Initially prepared acid-capped CdSe nanotetrapods ones exhibit band edge as well as trap emission,9 with rather poor PL quantum yield (PLQY). The band edge emission exhibits trapping times of 1 ps and 8 ps, while the red shifted, broad trap emission has a lifetime in tens of ns.10 They are assigned to processes that lead to the population of radiative and nonradiative trap states, respectively. Preponderance of nonradiative traps makes these nanotetrapods poorly emissive, even though there is an increase in PLQY by an order of magnitude compared to the dual emissive nanotetrapods. In the quest for strong PL, nanotetrapods have been doped with Cu(I) and this has led to a red shifted charge transfer (CT) PL with significantly larger PLQY of 38% and lifetime of 500 ns.12 The trigger for this strong PL is provided by ultrafast hole capture by Cu(I) and consequent decrease in overlap between electron and hole wavefunctions. PL from water-soluble nanotetrapods remain elusive till date.11 However, Polyethyleneimine (PEI)-capped spherical CdS nanocrystals, prepared in aqueous medium, have been found to be strongly photoluminescent.13 The interplay of multiexciton processes and trap emission in these nanocrystals has been worked out carefully. The mechanism of selective turn-off PL sensing of Pb2+ by these nanocrystals, involving ultrafast electron and hole trapping, has been explored.14
1 S. Dasgupta, T. Khan, and A. Datta, in Springer Proc. Phys. (Springer, 2019), pp. 23–38.
2 T. Khan, S. Vaidya, D.S. Mhatre, and A. Datta, J. Phys. Chem. B 120, 10319 (2016).
3 T. Khan and A. Datta, J. Phys. Chem. C 121, 2410 (2017).
4 T. Khan and A. Datta, Phys. Chem. Chem. Phys. 19, 30120 (2017).
5 S. Dasgupta, S. Banerjee, S. Das, and A. Datta, Phys. Chem. Chem. Phys. (2021).
6 S. Dasgupta, A. Chowdhury, and A. Datta, J. Indian Chem. Soc. 98, 100122 (2021).
7 S. Rakshit, S. Das, P. Poonia, R. Maini, A. Kumar, and A. Datta, J. Phys. Chem. B 124, 7484 (2020).
8 S. Rakshit, S. Das, V. Govindaraj, R. Maini, A. Kumar, and A. Datta, J. Phys. Chem. B 124, 10282 (2020).
9 S. Banerjee, A. Gupta, R. Srivastava, and A. Datta, Phys. Chem. Chem. Phys. 20, 4200 (2018).
10 S. Banerjee, B.G. Maddala, F. Ali, and A. Datta, Phys. Chem. Chem. Phys. 21, 9512 (2019).
11 S. Banerjee, T. Kistwal, A. Sajeevan, and A. Datta, ChemPhysChem 21, 2709 (2020).
12 F. Ali, S. Das, S. Banerjee, B. Gopal Maddala, G. Rana, and A. Datta, 13, 14228 (2021).
13 S. Das, S. Rakshit, and A. Datta, J. Phys. Chem. C 124, 28313 (2020).
14 S. Das, S. Rakshit, and A. Datta, J. Phys. Chem. C 125, 15396 (2021).
About the speaker:
Dr. Anindya Datta is a full professor heading the Chemistry Department at IIT Bombay. He received PhD degree from Jadavpur University. He was a post-doctoral research fellow at Iowa State University USA.
He has served as Head, Center for Research on Nanotechnology and Center for Sophisticated Analytical Instrumental Facility (CRNTS-SAIF) and Associate Dean (student Affairs) at IIT Bombay. His Primary research interest is on ultra-fast spectroscopy and microscopy of fluorescent species (molecules, quantum dots, etc.), particularly, on their dynamics affecting the emissive behavior. He is a Fellow of National Academy of Sciences, India and has received CRSI Bronze medal for excellent research. He is a Member of Editorial Advisory Board of The Journal of Physical Chemistry. He is well-known for his teaching abilities and has received Departmental award for Excellence in Teaching. He has published numerous papers, and book chapters and has guided many PhD students.