Investigation of naphthalenediimide and phenothiazine derivatives as photoinduced charge separation junctions

Abstract

Phenothiazine derivatives present low oxidation potentials and oxidized species with high stability, entitling them as good $\pi$-electron donors. Naphtalenediimide (NDI) is an efficient electron acceptor due to its high electron affinity while ambient air-stable. NDI can be easily synthesized with siloxy groups permitting the fabrication of silicate films and mesoporous materials using sol-gel chemistry. We have investigated $\pi$-stacked junctions of bis-triethoxysilylpropyl-Naphthalenediimide (NDI-silane) with Methylene Blue [3,7-Bis(di-methylamino) phenothiazin-5-ium chloride, MB], phenothiazine tert-butyl [3,7-di-t-butylphenothiazine, TBP], and their 1,10'-dimers (MB-DI and TBP-DI, respectively) using Time-Dependent Density Functional Theory (TD-DFT) with the optimally tuned range separated hybrid (OT-RSH) functional. From simple designing rules, as ionization potential matches, we note that the junction TBP-NDI-silane is quite promising. It shows the correct alignment between the ionization energy of the donor with the electron affinity of the acceptor. It also demonstrates the first two excited states with a strong charge-transfer character. These transitions are at ``sunlight accessible'', at 1.46 and 2.84 eV, with non-negligible oscillator strengths, 0.015 and 0.020, respectively. In this project, we propose to investigate the influence of a heterogeneous environment in TBP-NDI-silane thin films with respect to the optical properties and photoinduced charge transfer efficiency. (AU)