Metallocene-Naphthalimide Derivatives: The Effect of Geometry, DFT Methodology, and Transition Metals on Absorption Spectra

Abstract

In the present paper, the photophysical properties of metallocene-4-amino-1,8-naphthalimide-piperazine molecules (1-M2+), as well as their oxidized and protonated derivatives (1−M3+, 1-M2+-H+, and 1-M3+-H+), where M = Fe, Co, and Ni, were studied via DFT and TD-DFT, employing three functionals, i.e., PBE0, TPSSh, and wB97XD. The effect of the substitution of the transition metal M on their oxidation state, and/or the protonation of the molecules, was investigated. The present calculated systems have not been investigated before and, except for the data regarding their photophysical properties, the present study provides important information regarding the effect of geometry and of DFT methodology on absorption spectra. It was found that small differences in geometry, specifically in the geometry of N atoms, reflect significant differences in absorption spectra. The common differences in spectra due to the use of different functionals can be significantly increased when the functionals predict minima even with small geometry differences. For most of the calculated molecules, the main absorption peaks in visible and near-UV areas correspond mainly to charge transfer excitations. The Fe complexes present larger oxidation energies at 5.4 eV, whereas Co and Ni complexes have smaller ones, at about 3.5 eV. There are many intense UV absorption peaks with excitation energies similar to their oxidation energies, showing that the emission from these excited states can be antagonistic to their oxidation. Regarding the use of functionals, the inclusion of dispersion corrections does not affect the geometry, and consequently the absorption spectra, of the present calculated molecular systems. For certain applications, where there is a need for a redox molecular system including metallocene, the oxidation energies could be lowered significantly, to about 40%, with the replacement of the iron with cobalt or nickel. Finally, the present molecular system, using cobalt as the transition metal, has the potential to be used as a sensor.

Molecular Logic Gates Based on Ferrocene-Containing Compounds

“…B3LYP has been used for theoretical calculations of ferrocene [16]. However, PBE0 is the functional that has yielded the most accurate results in the prediction of the ferrocene properties [19]. The Minnesota family functionals M06 [84] have also become very popular, while long-range corrected hybrid functionals wB97, wB97X, wB97X-D, and wB97X-2 could be used as well.…”

“…Tzeliou and Tzeli [19] studied, via DFT and TD-DFT, the photophysical properties of metallocene-4-amino-1,8-naphthalimide-piperazine molecules (1-M 2+ ), and their oxidized and protonated derivatives (1-M 3+ , 1-M 2+ -H + , and 1-M 3+ -H + ), where M = Fe, Co, and Ni, employing three functionals, i.e., PBE0, TPSSh, and wB97XD. The calculated systems had not been investigated before.…”

“…Ferrocene can easily donate an electron in a molecular system designed according to the principles of modular photoelectron transfer, i.e., in the 'fluorophore−spacer−receptor' or 'fluorophore−spacer−receptor1−spacer−receptor2 ′ format via redox chemistry. Thus, ferrocene derivatives have potential applications as MLG systems [17][18][19][20].…”

“…Finally, a summary of the previous experimental and theoretical MLG studies on compounds containing the ferrocene moiety is presented in Table 1. [23] (expt) NOT [19] (th) [20] (expt + th); [22] (expt) PASS 5 [17] (expt + th); 6 [17] (expt + th); 13 [41] (expt) [20] (expt + th); [23] (expt + th)…”

“…[51] (th); [30] (expt); [31] (expt); [32] (expt) [22] (expt + th); [23] (expt + th); [26] (expt); [28] (expt); [60] (expt) NAND [19] (th) [20] (expt + th); [60] (expt)…”