Room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) in molecular materials having only lighter elements is a fascinating phenomenon due to its diverse potential applications, including organic light-emitting devices (OLEDs), lighting systems, solar cells, and sensors, and bioimaging. However, in most organic compounds, the triplet state is considered a dark state because of its low emissive nature due to the weak spin-orbit coupling among lighter elements. Thus, realizing emission from the triplet state of purely organic molecules is a challenging task. For TADF materials, the critical design strategy involves reversing the triplet population to a vibronic sub-level that is isoenergetic with the emissive singlet states by enabling reverse intersystem crossing (RISC) via preferably an energy conserved process. On the other hand, the prerequisite to achieve efficient RTP is the maximum overlap between excited singlet and triplet states and the minimum energy gap between S1 and T1 and strong SOC. Thus, to maximize ISC/RISC, ΔEST should be minimized. These requirements can be achieved by designing a molecular architecture having excited states with strong charge-transfer character (CT). Such molecules typically have minimal spatial overlap between the highest occupied (HOMO) and lowest unoccupied molecular orbitals (LUMO), respectively. However, the large spatial separation of frontier molecular orbitals (FMOs) not only reduces the ΔEST value but also reduces the oscillator strength of the transition. The temperature dependence and low oscillator strength collectively affect the luminescence quantum yields of luminophores, which is the most critical parameter in real-life applications. Thus, developing an alternative design strategy to produce strongly luminescent molecules with improved PL quantum efficiency is of fundamental importance. We are actively involved in designing and developing efficient RTP and TADF molecules. We are also interested in understanding the role of main-group elements in controlling conjugated molecular systems' delayed optical properties. The compounds developed are subject to a broad range of applications, including Sensing, bio-imaging, and optical devices.



  1. 1. Effect of Branching on the Delayed Fluorescence and Phosphorescence of Simple Borylated Arylamines.

  2. K. K., Neena. P. Sudhakar; P. N. Rajendra; P. Thilagar, Inorg. Chem. 2020, 59(5), 3142-3151.

  3. 2. Triarylborane‐Appended Anils and Boranils: Solid‐State Emission, Mechanofluorochromism, and Phosphorescence.

  4. N. R. Prasad, P. Sudhakar, K. K. Neena, and P. Thilagar, Chem. Eur. J. 2020, (26), 1–13

  5. 3. Delayed Fluorescence, Room Temperature Phosphorescence, and Mechanofluorochromic Naphthalimides: Differential Imaging of Normoxia and Hypoxia Live Cancer Cells.

  6. S. Jena, P. Dhanalakshmi, G. Bano, P. Thilagar, J. Phys. Chem. B., 2020, 124, 26, 5393–5406.

  7. 4. Design, Synthesis, and Temperature-Driven Molecular Conformation-Dependent Delayed Fluorescence Characteristics of Dianthrylboron-Based Donor-Acceptor Systems.

  8. U. P. Pandey, N. R. Prasad, P. Thilagar, Front Chem. 2020, 8, 541331. ( An invited article for a themed issue on “ Thermally Activated Delayed Fluorescence (TADF)). 

  9. 5. Room Temperature Phosphorescent (RTP) N-​Acetylphenothiazines

  10. Sarkar, S. K. Sarkar, P. Thilagar, ChemPhotoChem 2020, 4(4), 282-286.

  11. 6. Aggregation-​Induced and Polymorphism-​Dependent Thermally Activated Delayed Fluorescence (TADF) Characteristics of an Oligothiophene: Applications in Time-Dependent Live Cell Multicolour Imaging

  12. S. K. Sarkar, M. Pegu, S. K. Behera, Santosh Kumar; N. Siva Krishna; P. Thilagar, Chem.Asian J., 2019, 14,4588 –4593. An invited article for a themed issue on the 20th anniversary of CRSI

  13. 7. Room temperature phosphorescent triarylborane functionalized iridium complexes

  14. G. Rajendra Kumar, S. Kumar Behera, and P. Thilagar. Dalton. Trans., 2019, 48, 6817. (an invited article for the themed issue on “ Inorganic Chemistry of the p-Block Elements ” in Dalton Transactions).

  15. 8. Catalyst- and Template-Free Ultrafast Visible-Light-Triggered Dimerization of Vinylpyridine-Functionalized Tetraarylaminoborane: Intriguing Deep-Blue Delayed Fluorescence.

  16. K. K. Neena, P. Sudhakar, and P. Thilagar.Angew.Chem. Int. Edn., 2018, 57(51), 16806-16810.

  17. 9. Tuning the Phosphorescence and Solid State Luminescence of Triarylborane-Functionalized Acetylacetonato Platinum Complexes

  18. G Rajendra Kumar and P. Thilagar. Inorg. Chem., 2016, 55, 12220-12229

  19. 10. Recent advances in purely organic phosphorescent materials

  20. Sanjoy Mukherjee and P. Thilagar, Chem. Commun., 2015, 51, 10988-11003  (Appeared as inside front cover page article).