Nanophotosensitizing through Space Charge Transfer Assemblies of Pentacenequinone Derivative for 'Metal-free' Photoamidation Reactions.

Abstract

The present study demonstrates the influence of small portion (20 %) of organic co-solvent (DMSO/THF/ACN/MeOH) in mixed aqueous media (80 % water) in controlling the size, quantum yield and life time of the through space charge transfer assemblies (TSCT) of pentacenequinone derivative (TPy-PCQ-TPy). Among various solvent systems [H2 O : DMSO (8 : 2), H2 O : THF (8 : 2), H2 O : ACN (8 : 2) and H2 O : MeOH (8 : 2)] examined, highly emissive (Φf =12 %) and nano-sized assemblies having long life time (3.11 ns) were formed in H2 O : DMSO (8 : 2) solvent system. The solvent dependent differences in the size and excited state properties of TPy-PCQ-TPy assemblies are reflected in their photosensitizing behaviour in different solvent systems. Backed by excellent photosensitizing properties, TPy-PCQ-TPy assemblies smoothly catalyse the photoamidation reactions between unactivated/activated aldehydes and secondary amine under mild reaction conditions (visible light irradiation, aerial atmosphere, room temperature) in H2 O : DMSO (8 : 2) solvent mixture. The as prepared assemblies of TPy-PCQ-TPy also exhibit high potential to catalyse the oxidation of benzyl alcohols to aromatic aldehydes, thus, generating a possibility to use aromatic alcohols as the starting material in photoamidation reactions. The real time application of TSCT assemblies has also been demonstrated in gram scale transformation of aromatic aldehydes to aromatic amides and photooxidation of benzyl alcohol to aromatic aldehyde.