Ph. D. Thesis Colloquium
Name: Mr. Manoj Kumar Sharma
Research Supervisor: Prof. Satish Patil
Title: Hamilton-Receptor-Guided Supramolecular Assembly of Pentacene: Directing J-/H-Aggregation and Intermolecular Coupling for Singlet Fission
Date and Time: Monday, 27th July at 11:00 a.m.
Venue: Rajarshi Bhattacharyya Memorial Lecture Hall, Chemical Sciences Building
Abstract:
Singlet fission (SF) is a spin-allowed multiexciton generation process in which one photoexcited singlet exciton is converted into two triplet excitons, offering a promising pathway to surpass the conventional efficiency limits of photovoltaic devices.1 While satisfying the thermodynamic energy criterion is essential, the efficiency and kinetics of SF are governed predominantly by electronic coupling2, which is exquisitely sensitive to chromophore packing. Despite extensive investigations across a wide range of chromophores, control on molecular packing remains one of the most significant unresolved challenges in the field. Conventional π-conjugated materials rely primarily on van der Waals interactions, leading to packing motifs that are difficult to predict or systematically tunable.3 As a result, fine-tuning of intermolecular electronic coupling generally demands substantial synthetic effort.4.
In this thesis, I have explored the use of supramolecular polymers as a versatile platform for singlet fission. Directional hydrogen bonding5,6 is employed to organize acene chromophores into well-defined supramolecular architectures, enabling precise control over intermolecular packing and electronic coupling. This approach exploits reversible, highly directional noncovalent interactions to access a broad range of coupling regimes within a single molecular platform. Remarkably, this strategy leads to the formation of a J-aggregate in a pentacene-based system, a rare packing motif that has remained largely inaccessible in pentacene assemblies.7 These supramolecular architectures provide an effective way to modulate SF dynamics by controlling intermolecular interactions rather than redesigning the chromophore itself.
Beyond solution-phase assemblies, this work further addresses the challenge of translating optimized molecular organization into the solid state, a limitation imposed by van der Waals interactions. Here, we demonstrated that directional hydrogen bonding effectively preserves the structural organization during solution-to-film processing. Consequently, the packing motif, electronic coupling, and singlet fission dynamics remain largely conserved, highlighting the ability of supramolecular interactions to impart structural memory and offering an attractive strategy for developing solution-processable SF materials.
In addition, a serendipitous observation during the doping of these supramolecular assemblies with the Lewis acid SbCl5 revealed unexpected electronic behavior, opening a new avenue for investigating their structure-property relationships. Collectively, these findings establish supramolecular self-assembly as a powerful molecular design principle for controlling electronic coupling and tuning singlet fission dynamics with a level of precision that is difficult to achieve through conventional covalent synthesis alone. This work provides a comprehensive framework for the rational design of next-generation singlet fission materials.
References:
(1) Smith, M. B.; et al. Singlet Fission. 2010, 6891–6936.
(2) Miyata, K.; el al, Chem. Rev. 2019, 119 (6), 4261–4292.
(3) Walker, B. J.; et al. Nat. Chem. 2013, 5 (12), 1019–1024. h
(4) Majumder, K.; et al. J. Am. Chem. Soc. 2023.
(5) Sharma, M. K.; et al. ACS Omega 2023, 5 (9), 5093–5102.
(6) Maity, N.; et al. Nat. Commun. 2022, 13 (1), 1–14.
(7) Sharma, M. K.; et al. J. Am. Chem. Soc. 2025, 147 (38), 34989–35001.