Substituent effects on the optical properties of naphthalenediimides: A frontier orbital analysis across the periodic table

Abstract

A comprehensive theoretical treatment is presented for the electronic excitation spectra of ca. 50 different mono-, di-, and tetrasubstituted naphthalenediimides (NDI) using time-dependent density functional theory (TDDFT) at ZORA-CAM-B3LYP/TZ2P//ZORA-BP86/TZ2P with COSMO for simulating the effect of dichloromethane (DCM) solution. The substituents -XHn are from groups 14-17 and rows 2-5 of the periodic table. The lowest dipole-allowed singlet excitation (S0 -S1 ) of the monosubstituted NDIs can be tuned from 3.39 eV for -F to 2.42 eV for -TeH, while the S0 -S2 transition is less sensitive to substitution with energies ranging between 3.67 eV for -CH3 and 3.44 eV for -SbH2 . In the case of NDIs with group-15 and -16 substituents, the optical transitions strongly depend on the extent to which -XHn is planar or pyramidal as well as on the possible formation of intramolecular hydrogen bonds. The accumulative effect of double and quadruple substitution leads in general to increasing bathochromic shifts, but the increased steric hindrance in tetrasubstituted NDIs can lead to deformations that diminish the effectiveness of the substituents. Detailed analyses of the Kohn-Sham orbital electronic structure in monosubstituted NDIs reveal the mesomeric destabilization of the HOMO as the primary cause of the bathochromic shift of the S0-S1 transition.

Rational design of near‐infrared absorbing organic dyes: Controlling the HOMO–LUMO gap using quantitative molecular orbital theory

“…Introducing a π‐donating NH 2 (X in Scheme ) substituent on the benzene ring (D2) increases its HOMO energy (C 6 H 4π,HOMO ), whereas a π‐accepting CN (Y in Scheme ) substituent (A2) lowers its LUMO energy (C 6 H 4π*,LUMO ), resulting in both cases in a decrease of Δ E frag H‐L (Fig. b) in qualitative agreement with recent studies . The HOMO arises from the antibonding combination of the occupied D1 π,HOMO and NH 2π,HOMO fragment orbitals, whereas the LUMO originates from the bonding combination of the unoccupied A1 π*,LUMO and CN π*, LUMO fragment orbitals.…”

Performance of TDDFT Vertical Excitation Energies of Core‐Substituted Naphthalene Diimides

“…All the equilibrium geometries were verified by vibrational analyses to be (local) minimum energy structures (zero imaginary frequencies). The frontier orbital wavefunctions exhibit a nodal plane at the two nitrogen positions in the diimide ring, which suggests that the alkyl or phenyl groups at these positions would have no significant impact on the molecular electronic properties . We found exactly the same observation.…”

“…In this paper we present a systematic TDDFT study of core‐substituted naphthalene diimides (cNDIs) which are well known for their tunable absorption and emission properties, ranging over the entire visible to near‐infrared spectrum . The parent NDI molecule has been extensively used as an electron acceptor exhibiting a high π‐acidity, as well as for electron transport and photoinduced CT applications .…”

Systematic Computational Design and Optimization of Light Absorbing Dyes

“…This way of substitution is found to be most common in the literature. 21 , 25 , 28 , 54 Using CAT, a total of 1015 NDI derivatives are generated: 7 mono-substituted, 28 di-substituted, 343 tri-substituted, and 637 tetra-substituted derivatives. The molecule sizes vary from 33 to 106 atoms.…”

“…It is shown that electron-donating functional groups like alkoxy, 25 , 26 alkylamino, 26 alkylthio, 25 and thiophenes 27 affect optical properties via electronic effects (mainly mesomeric and inductive) on the frontier molecular orbitals, causing a decrease of the HOMO/LUMO gap while increasing the HOMO and LUMO energies. 28 , 29 The lowest transition in NDI is susceptible to the substituent effect, while the higher transition is unaltered and resembles the properties of non-substituted NDI. 21 , 25 …”