Modelling the quenching effect of chloroaluminum phthalocyanine and graphene oxide interactions: implications for phototherapeutic applications.

Photodynamic therapy (PDT) and photothermal therapy (PTT) are promising candidates for cancer treatment and their efficiency can be further enhanced by using a combination of both. While chloroaluminum phthalocyanine (AlClPc) has been studied extensively as a photosensitizer in PDT, nanographene oxide (nGO) has shown promise in PTT due to its high absorption of near-infrared radiation. In this work, we investigate the energy transport between AlClPc and nGO for their combined use in phototherapies. We use density functional theory (DFT) and time-dependent DFT to analyze the electronic structure of AlClPc and its interaction with nGO. Based on experimental parameters, we model the system's morphology and implement it in Kinetic Monte Carlo (KMC) simulations to investigate the energy transfer mechanism between the compounds. Our KMC calculations show that the experimentally observed fluorescence quenching requires modeling both the energy transfer from dyes to nGO and a molecular aggregation model. Our results provide insights into the underlying mechanisms responsible for the fluorescence quenching observed in AlClPc/nGO aggregates, which could impact the efficacy of photodynamic therapy.

Dynamical exciton decay in organic materials: the role of bimolecular recombination.

Excitons play a critical role in light emission when it comes to organic semiconductors. In high exciton concentration regimes, monomolecular and bimolecular routes for exciton recombination can yield different products affecting significantly the material's optical properties. Here, the dynamical decay of excitons is theoretically investigated using a kinetic Monte Carlo approach that addresses singlet exciton diffusion. Our numerical protocol includes two distinct exciton-exciton interaction channels: exciton annihilation and biexciton cascade emission. Our findings reveal that these channels produce different consequences concerning diffusion and spectroscopic properties, being able to explain diverging experimental observations. Importantly, we estimate critical exciton densities for which bimolecular recombination becomes dominant and investigate its effect on average exciton lifetimes and diffusion lengths.