Excited-State Carrier Dynamics in Semiconducting Heterostructures from Self-Sorted NIR Active Dyes

Heterostructures comprise two or more different semiconducting materials stacked either as co-assemblies or self-sorted based on their dynamics of aggregates. However, self-sorting in heterostructures is rather significant in improving the short exciton diffusion length and charge separation. Despite small organic molecules being known for their self-sorting nature, macrocyclic are hitherto unknown owing to unrestrained assemblies from extended π-conjugated systems. Herein, two near infrared region (NIR) active molecules comprised of porphyrin appended D-π-D (1) and A-π-A (2) have been reported to show the self-assembled 0D and 2D nanostructures via J-aggregates. Interestingly, the mixture of 1 and 2 reveals self-sorting at the molecular level promoting nanosphere and sheet structures which further rolled over to spheres through π-π stacking leading to core-shell type heterostructure. Consequently, electrical conductivity is 10 times higher than the individual assemblies due to excited state electron transfer from 1 to 2 in a mixture, confirmed by femto second-transient absorption spectroscopy and electrochemical impedance spectroscopy. These results suggest that controlling the self-sorted heterostructures fosters refining the electronic properties which pave the way for designing novel NIR-absorbed molecules for organic solar cells (OSCs).