Research Projects

Design and development of metal-free pure organic systems that can simultaneously generate singlet oxygen (¹O₂) with improved efficiency and have the ability to regulate the ¹O₂ generation process with accurate control remain under-explored. This project aims at developing metal-free water soluble pure organic photoswitchable molecules and amphiphiles which by virtue of their photoswitchability, can regulate the ¹O₂ generation and can be applied in controlled photodynamic therapy (PDT) in a non-invasive way. To make the PDT non-invasive, we design all the systems such that the photoisomerization process should be triggered by visible and NIR light only avoiding the UV lights as stimuli. Diarylethene (DAE) will be our choice as a photoswitching control unit due to its high thermal stability, robust fatigue resistance property and the presence of two distinctly different absorbance maxima for the two isomeric states. The visible light triggered switching might be achieved by using salicylidene-based intramolecular proton transfer (IPT) unit and diacetyl-based photosensitization methods where both the units (IPT and diacetyl) must be attached to the DAE in a conjugated manner. Further, in order to obtain visible light induced switching of DAE, a suitable triplet sensitizer (pyromellitic unit) will be introduced in a conjugated manner for triplet-triplet energy transfer (TTET) from the sensitizer to the DAE unit. From this point of view, the sensitizer will be designed in such a manner that the excitation of the sensitizer does not interfere the photoswitching phenomenon of DAE and the emission of the sensitizer must have sufficient spectral overlap with the absorption bands of closed isomer of DAE (not open form) for “on-demand activation-deactivation” of ¹O₂ generation process. Further, the NIR light driven photoisomerization process will be carried out by the core structural modification of DAE, where the ethene bridge of the DAE unit will be modified with highly electron deficient moieties. Importantly, all the sensitizers will be meticulously constructed to have stable triplet state to effectively transfer energy to the ambient triplet oxygen to generate highly reactive ¹O₂. Among all, few proposed molecules are expected to function in monomeric state whereas other proposed amphiphiles are expected to assemble as micellar nanoaggregate and to demonstrate enhanced ¹O₂ generation capability in aggregated state more elegantly as PDT agents as nanoaggregates based therapeutic agent often offer minimal damage to surrounding healthy tissues. We envisage that our proposed study will pave a new avenue to develop metal-free pure organic photoswitchable molecules for the tunable generation of ¹O₂ in monomeric as well as nanoaggregates in water as efficient PDT agents with precise control.