Theoretical Investigation on the Kinetics and Mechanism of the Synthesis of Fluorescent 3,8-Disubstituted-3H-Imidazo [4,5-a] Acridine-11-Carbonitriles

Abstract

3,8-Disubstituted-3H-imidazo[4,5-a]acridine-11-carbonitriles show very interesting optical properties. In some cases, they have higher quantum yields compared to well-known fluorescent dyes such as fluorescein. Hitherto, no detailed theoretical study has been reported on the mechanism of the synthesis of the titled compounds, hence an accurate and detailed theoretical investigation on the synthesis of these dyes is desirable. In this paper, density functional theory (DFT) methods have been employed to investigate the most reasonable mechanism in formation of these fluorophores. All species and related transition states were optimised and the relative energies of all species and the activation energies for all proposed mechanisms were obtained. Comparing the Ea values of all pathways reveals that intramolecular electrophilic aromatic substitution is the most plausible mechanism for the cyclisation reaction in the preparation of these dyes. Also, the effects of substituents in positions 3 and 8 were investigated and the results show that electron-donor substituents can reduce the activation energy for formation of the σ complex in the electrophilic aromatic substitution.

Synthesis, characterisation, optical properties and theoretical calculations of a new fluorescent heterocyclic system: 3H-benzo[a]pyrazolo[3,4-j]acridine

“…Recently, we performed DFT calculations using the B3LYP hybrid functional and the 6-311++G(d,p) basis set to gain the most reasonable mechanism for the formation of 3H-imidazo [4,5-a]acridines. 28 The results obtained revealed that intramolecular electrophilic aromatic substitution is the most likely mechanism for cyclisation of the intermediate in these reactions. According to these results, 28 the most plausible reaction mechanism to explain the formation of fluorophores 3a-d involves the attack of the anion derived from 2 on compounds 1a-d and the generation of intermediates A and A′ followed by dehydration of A′′ and the formation of intermediate B in basic media, as depicted in Scheme 2.…”

“…28 The results obtained revealed that intramolecular electrophilic aromatic substitution is the most likely mechanism for cyclisation of the intermediate in these reactions. According to these results, 28 the most plausible reaction mechanism to explain the formation of fluorophores 3a-d involves the attack of the anion derived from 2 on compounds 1a-d and the generation of intermediates A and A′ followed by dehydration of A′′ and the formation of intermediate B in basic media, as depicted in Scheme 2. Finally, intramolecular electrophilic aromatic substitution of C to D led to the formation of the compounds 3a-d.…”

Synthesis, electrochemical, photophysical, and photovoltaic properties of new fluorescent compounds: 3 H ‐benzofuro[2,3‐ b ]pyrazolo[4,3‐ f ]quinoline

“…As depicted in Scheme 2, the mechanism behind the preparation of the novel 3a ‐ e can be considered to be as follows 43 . The attack of the anion 2 on the compounds 1a‐e produces the intermediates A and A′ followed by the dehydration of A″ and the preparation of intermediate B in alkaline solution.…”

“…The details of the photoelectrochemical measurements can be found in our earlier studies 42,43 . As represented in Figures 5 and 6, the I ‐ V curves and the IPCE spectra of the heterocyclic compounds 3a‐e have been subjected to investigation.…”