of DFT Calculations in Designing Naphthalimide-π- Dimethylanilines

Abstract

The introduction of density functional theory (DFT) has tremendously aided the application of computational material science in the design and development of organic materials. The use of DFT and other computational approaches avoids time-consuming empirical processes. Therefore, this review explored how the DFT computation may be utilized to explain some of the features of organic systems. First, we went through the key aspects of DFT and provided some context. Then we looked at the essential characteristics of an organic system that DFT simulations could predict. Gaussian software had been employed with the B3LYP functional and 6-31G(d, p) basic sets for organic systems.

Keywords

• DFT
• organic materials
• B3LYP
• 6-31G(d
• p) basic sets

1. Introduction

2. Experimental section

Computational details

Quantum chemical calculations of studied derivatives were performed using DFT and TD-DFT implemented in the Gaussian 16 [5] software package. Geometry optimization was provided by means of density functional CAM-B3LYP method and 6-31g(d,p) basis set in the ground S0 state as well as the lowest excited S1 state. Solvent surrounding (cyclohexane, acetonitrile) was simulated using PCM method. The evaluation of the twisted excited states was carried on with semi-empirical MOPAC, using PM7 Hamiltonian, including solvent with COSMO model [6].

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3. Results and discussion

DFT modelling, intramolecular charge transfer

Optimized ground state geometries and charge density distributions in HOMO and LUMO states of compounds NA1 and NA2 in cyclohexane (CyHex) are depicted in Figure 1. Both molecules reveal a CT nature of electronic transition. The HOMO state comprises charge redistribution between NI and DMA moieties, while the charge density in the LUMO state is localized mainly on NI core. The studied compounds show different twist angles between NI and DMA moieties. Compound NA1 with phenyl ring as a π-linker has a pre-twisted geometry in a ground state: the twist angle between dimethylamine and benzene (ϕ1) is 9°, while between NI and DMA (ϕ2) is 51°. state geometry changes were noted in solvents of higher dielectric constant (Table 1). The energies of upwards transitions of singlets states as well as a short comment on the excited state optimization are provided in Table 2. EMAIL: [e-mail] (D. Gudeika)

2023 Copyright for this paper by its authors. energies of electronic transitions S0→S1 and S1→S0 in different solvents.

1 ϕ1 denotes angle between dimethylamine and benzene ring.

2 ϕ2 denotes angle between naphthalimide unite and benzene ring.

3 Angles between dimethylamine and benzene ring (ϕ1) and between naphthalimide unit and benzene ring (ϕ2) in the excited state geometry. For the comment on the obtained values, see text below

The optimisation of the potential surface of the lowest excited singlet when varying the twist angle was not successful with selected long-range separated functional CAMB3LYP and PCM solvent model, i.e., no significant twist was obtained in acetonitrile and the calculated transition energies (S1→S0) reassembles only the blue fluorescence spectra band. On the other hand, the semi-empirical evaluation with PM7 Hamiltonian of MOPAC (with solvent model COSMO) allowed to reproduce the twisted geometries of NI compounds in most polar environment, as showed in Figure 2. EMAIL: [e-mail] (D. Gudeika)

2023 Copyright for this paper by its authors. dimethylaniline for NA1 (a) and NA2 (b) in non-polar (with ε=1) and polar (with ε=20) environments, obtained with semi-empirical method (PM7 Hamiltonian of MOPAC, solvent model

COSMO). Table 2. The calculated ground state dipole moments.

4. Conclusions

Two new twisted intramolecular charge transfer (TICT) donor-π-acceptor compounds were designed by combining a well-known electron acceptor naphthalimide unit with a classic electron donor dimethylaniline through two types of different rigid linkers. The increase of solvent polarity determines the competition between CT and TICT states.The pre-twisted geometry of compound has no influence in terms of excited state reaction rates. On the other hand, the higher difference between ground and excited state dipole moments determines faster excited state processes.

5. Acknowledgements

We thank R. Skaisgiris for the contribution at the early stages of the project. EMAIL: [e-mail] (D. Gudeika)

2023 Copyright for this paper by its authors.

6. References

multifunctional drug delivery systems:

References

[1] K. A. Baseden , J. W. Tye , Introduction to density functional theory: calculations by hand on the