Twisted intramolecular charge transfer (TICT) is an electron transfer process that occurs upon photoexcitation in molecules that usually consist of a donor and acceptor part linked by a single bond. Following intramolecular twisting, the TICT state returns to the ground state through weak red-shifted emission or nonradiative relaxation. Nowadays, several TICT-based materials have been discovered to become fluorescent upon aggregation. Recently, twisted intramolecular charge transfer (TICT) combined with aggregated induced emission (AIE) based work has received much attention in biological applications. These integrated features (TICT+AIE) were effective in selectively staining cancer cells from normal cells and helped build a promising system for long-term cell tracking. The strong D−A effect causes TICT+AIE to exhibit a large stokes shift with high intensity, which minimizes the cross-talk between the excitation source and fluorescent emission enabling cellular imaging with a high signal-to-noise ratio. Combining TICT and AIE properties in one molecule is an efficient technique to achieve changes in the emission spectra in the aggregated state and offers advantages such as i) improved photo-stability ii) better reproducibility iii) boosting photothermal property iv) sensitive temperature sensing.
In this paper, we developed a TICT+AIE based system that distinguishes normal and cancer cells and is applied to deliver anticancer drugs. To the best of our knowledge, for the first time, we developed TICT and AIE active green light responsive D–π–A naphthayridine-BODIPY photocages, which accomplish both. The emission of Naph-BODIPY was examined in various solvents and found to be dependent on the polarities of solvents, which indicates the TICT character. The emission intensity of the compound also enhances with the increasing water fraction in DMSO and the system's viscosity, demonstrating the typical AIE property. Encouragingly, the TICT-AIE properties of Naph-BODIPY indicated its potential as an intense orange-emission source in the solid state. Interestingly, methyl substituted naphthyridine PRPGs showed faster photorelease than without methyl substituted naphthyridine PRPGs. The difference in the photorelease rate was investigated and supported by DFT calculations.

Scheme:TICT + AIE Active Naphthyridine-BODIPY as a PRPG

Moumita Banerjee

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