@article {48939, title = {Isomer effect on energy storage of π-extended S-shaped double[6]heterohelicene}, journal = { Angewandte chemie-international edition}, volume = {62}, year = {2023}, month = {NOV}, type = {Article}, abstract = {

Recently, chiral and nonplanar cutouts of graphene have been the favorites due to their unique optical, electronic, and redox properties and high solubility compared with their planar counterparts. Despite the remarkable progress in helicenes, pi-extended heterohelicenes have not been widely explored. As an anode in a lithium-ion battery, the racemic mixture of pi-extended double heterohelical nanographene containing thienothiophene core exhibited a high lithium storage capability, attaining a specific capacity of 424 mAh g-1 at 0.1 A g-1 with excellent rate capability and superior long-term cycling performance over 6000 cycles with negligible fade. As a first report, the pi-extended helicene isomer (PP and MM), with the more interlayer distance that helps faster diffusion of ions, has exhibited a high capacity of 300 mAh g-1 at 2 A g-1 with long-term cycling performance over 1500 cycles compared to the less performing MP and PM isomer and racemic mixture (150 mAh g-1 at 2 A g-1). As supported by single-crystal X-ray analysis, a unique molecular design of nanographenes with a fixed (helical) molecular geometry, avoiding restacking of the layers, renders better performance as an anode in lithium-ion batteries. Interestingly, the recycled nanographene anode material displayed comparable performance. A pi-extended double heterohelical nanographene of thienothiophene core fused with two hexabenzocoronene units exhibits excellent performance as an anode in a lithium-ion battery. The isomer (PP and MM) with more interlayer distance exhibited a high lithium storage capability compared to the other isomer and racemic mixture. Helical nanographene anodes display excellent rate capability, superior long-term cycling performance, and recyclability.image

}, keywords = {Battery, graphene, Li-ion battery, nanographene, Organic Electrode Material}, issn = {1433-7851}, doi = {10.1002/anie.202311657}, author = {Kumar, Viksit and Bharathkumar, H. J. and Dongre, Sangram D. and Gonnade, Rajesh and Krishnamoorthy, Kothandam and Babu, Sukumaran Santhosh} } @article {49607, title = {Chiroptical amplification of [7]-helicene nanographene by additional helical chirality}, journal = {Angewandte Chemie-International Edition}, volume = {64}, year = {2025}, month = {FEB }, pages = {e202420767}, type = {Article}, abstract = {

Nanographenes have captivated scientific interest since the pioneering discovery of graphene. Recently, attention has shifted towards exploring chiral and nonplanar nanographenes, for their distinct optical, chiroptical, and electronic properties. Despite the growing acceptance of helicenes, the research on inducing helical chirality on pi-extended derivatives to boost chiroptical properties remains unattended. In our study, we introduce a new pi-extended [7]-helicene resulting from the condensation of diamines with 3,6-dibromophenanthrene-9,10-dione, complemented by two hexabenzocoronene arms in the periphery. Notably, the nanographene containing binaphtho-[1,4]diazocine, compared to the corresponding phenazine, exhibits a remarkable average 2.5, 5, and 10-fold enhancements in quantum yield, dissymmetry factor, and brightness, respectively, when measured in five different solvents. These improvements underscore the significance of the induced helical chirality by the antiaromatic binaphtho-[1,4]diazocine in influencing the chiroptical properties of the helical nanographene. Our research represents a significant stride toward unlocking the potential of pi-extended helicenes and lays the groundwork for further exploration in designing and synthesizing new chiral nanomaterials.

}, keywords = {circularly polarised luminescence, dissymmetry factor, helicene, nanographene, quantum yield}, doi = {10.1002/anie.202420767}, author = {Dongre, Sangram D. and Venugopal, Geethu and Kumar, Viksit and Badrinarayan Jadhav, Ashok and Kumar, Jatish and Babu, Sukumaran Santhosh} } @article {49568, title = {Regioisomeric π-extended nanographene with long-lived phosphorescence afterglow}, journal = {Angewandte Chemie-International Edition}, volume = {64}, year = {2025}, month = {FEB}, pages = {e202422125}, type = {Article}, abstract = {

The cutouts of graphene sheets, particularly those with a nonplanar topology, present vast opportunities for advancement. Even a slight deviation from the planar structure can lead to intriguing (chiro)optical features for helically twisted nanographenes. In this context, we introduce two regioisomeric pi-extended nanographenes that exhibit distinct excited-state characteristics. The helicene structure and the photophysical features can be easily tuned by changing the connecting position of the nanographene to the carbazole core (2,7- and 3,6-). Single-crystal X-ray diffraction analysis confirmed the formation of nanographenes with bent and helical conformations. Both derivatives exhibited thermally activated delayed fluorescence at room temperature and phosphorescence at low temperatures. Notably, the nanographene with the bent structure displayed an impressive red afterglow lasting over 30seconds, in contrast to the very weak afterglow observed in the helical structure. DFT calculations revealed the existence of an isoenergetic higher triplet state (T-8) and comparatively weak spin-orbit coupling (T-1-S-0), thereby enabling the bent nanographene to exhibit a long-lived component and strong afterglow. Our findings highlight the significance of regioisomeric nanographenes with exceptional optical properties and offer a deeper understanding of the structure-property relationship in nonplanar nanographenes.

}, keywords = {Afterglow, CPL, Helicenes, nanographene, Phosphorescence, TADF}, doi = {10.1002/anie.202422125}, author = {Kumar, Viksit and Venugopal, Geethu and Jadhav, Ashok Badrinarayan and Dongre, Sangram D. and Gonnade, Rajesh and Kumar, Jatish and Ruer, Paul C. and Hupp, Benjamin and Steffen, Andreas and Babu, Sukumaran Santhosh} }