Deep Red emitting dicyanovinylene isophorone based chromophores: Combined synthesis, optical properties, viscosity sensitivity, and DFT studies

Abstract

Deep red emitting dicyanovinylene isophorone based dyes are synthesized and studied for photophysical properties, viscosity sensitivity, and DFT. The dyes consist of Carbazole and Triphenylamine donor and thiophene spacer together with one auxiliary accepter, –CN leads to deep red emission towards the NIR region (∼600−700 nm) in polar solvent media. All dyes show good emission solvatochromism with an increase in solvent polarity. The dyes show intramolecular (ICT) as well as “Twisted Intramolecular Charge Transfer (TICT)” which is reinforced by Lippert Mataga, MacRae, Weller, and Rettig plots. Viscosity induced emission enhancement study in ethanol/polyethylene glycol (PEG 400) system shows 4.34–4.85 folds increases emission intensity. ICT is supported by Frontier Molecular Orbital (FMO) diagram and bandgap energy. The observed experimental findings are also correlated with the computed values using “Density Functional Theory (DFT)”. The magnitudes of “first order hyperpolarizability”(β0) are 500−1000 × 10−30.e.s.u. while those of the “second order hyperpolarizability”(γ) are 3000−8300 × 10-36 e.s.u. Hence they can act as very good NLOphores. Mulliken Hush analysis and Natural Bond Orbital (NBO) analysis were used to support charge transfer characteristics.