N‐Ethyl Carbazole Derived D‐π‐A‐π‐D Based Fluorophores: Consolidated Spectroscopic, Viscosity and DFT Studies

Abstract

This article reports design and synthesis of three new fluorophores (5 a‐c) with the donor‐π‐acceptor‐π‐donor motif, where dicyano vinylene group is the central acceptor, N‐ethyl carbazole group is a fixed donor and varying the N‐substituted secondary donors so as to study their photophysical behavior. Based on the systematic photophysical and theoretical reconnaissances, the fluorophores structure‐property relationships are defined. Their spectral and photophysical behaviors are affected by the solvent polarity, with a significant bathochromic shift in emission and large Stoke shifts being observed in polar solvents. Contrary to dipolar asymmetric analogue this system shows an efficient intramolecular charge transfer as observed from various solvent polarity plots. For 5 a, 5 b, and 5 c, the viscosity induced emission studies show respectively 3.78, 6.53, and 6.82 times enhancement in their fluorescence intensity and hence act as a fluorescent molecular rotor (FMR). The structure and electronic properties of these fluorophores were evaluated using density functional theory computations using B3LYP/6‐311++G(d,p). The frontier molecular orbitals and the optimized geometry reveal that secondary donors in each fluorophore donate the electron and not the N‐ethyl carbazole group which is more twisted. The non‐linear and linear optical properties were determined employing solvatochromic and computational methods in solvents of varying polarities with results falling within the expected limiting values. The linear and non‐linear optical properties of the fluorophores change with the strength of different secondary donors used and solvent polarity. The two photon absorption cross‐section described using two level approximation is highest for 5 b (115‐172 GM).

New route for synthesis of 2-(2,2-dimethoxyethyl)-1,2,3,4,5,6-hexahydro-1,5-methanoazocino[4,3-b]indole and DFT investigation

“…On [24] by the same level of this work in 17.35-24.24 Â 10 À24 esu in the CHCl 3 . Also, the β tensor for the urea molecule, which is a prototype compound using for the comparison purpose, was reported [31] in 0.6230 Â 10 À30 esu.…”

“…Also, the chemical shifts for the C30, C37, and C41 have given the signals in 57.9, 52.6, and 53.2 ppm, respectively, and calculated in 68.0, 58.0, and 58.5 ppm (in CHCl 3 ). Recently, the aromatic 13 C chemical shifts for the carbazole substituted malononitrile derivatives were observed in 108.7-141.4 ppm, 108.8-151.0 ppm, and 108.6-150.4 ppm [24] and the unsaturated ring 13 C shifts for one of the studied compounds 21.0-60.4 ppm. Also, 13 C shifts for the aromatic and unsaturated rings of the hyperoside compound were reported [25] in 156.2-103.9 ppm and 71.2-60.1 ppm, respectively.…”

Donor–Acceptor Biarylcarbazoles as Efficient Host Materials for Solution-Processable High-Performance Phosphorescent Organic Light-Emitting Diodes

“…To introduce D–A functionalities onto the carbazole scaffolds, numerous synthetic approaches have been reported in the literature, which mainly include organometal-catalyzed reactions. − Sekar et al have reported carbazole-derived D−π–A−π–D-based fluorophores via condensation of 2-[1-(9-ethyl-9 H -carbazol-3-yl)­ethylidene]­malononitrile with different aldehydes . Zhao et al have synthesized carbazoles containing D–A cyclopropanes by regioselective N–H/C–H functionalization of carbazole in the presence of TfOH or Sc­(OTf) 3 , but these procedures require either expensive metal catalysts or harsh reaction conditions.…”