Polycyclic aromatic hydrocarbon-substituted push–pull chromophores: an investigation of optoelectronic and nonlinear optical properties using experimental and theoretical approaches

Abstract

IntroductionDonor-π-acceptor (D-π-A)-type push-pull chromophores, are well-known for their desirable features, such as tunable strong intramolecular charge-transfer bands that absorb light in a wide range of area including visible and near-IR regions, spectacular nonlinear optical properties, excellent solubility, and high thermal stabilities [1][2][3]. With these desired properties, push-pull chromophores have already been employed in a series of advanced applications such as photovoltaics, [4,5] light-emitting diodes, [6,7] sensors, [1,8,9] and NLO devices [1,10,11]. The successful integration of push-pull systems in high technology areas makes it necessary to design and synthesize new molecular structures with enhanced optoelectronic properties. However, synthetic strategies to access these entities are arguably limited and require multi-step protocols. The formal [2+2] cycloaddition-retroelectrocyclization (CA-RE) is one of the promising reaction candidates to circumvent these synthetic problems [1]. With its high-yielding nature and broad substrate scope, [2+2] CA-RE transformation occurs under very mild conditions without requiring a catalyst and fulfills all the requirements to be referred as a "click-type reaction" [12,13] [2+2] CA-RE transformation requires electron-rich alkynes and electrondeficient alkenes to synthesize nonplanar D-π-A systems [1]. Bruce and co-workers reported the first example of [2+2] CA-RE reactions between ruthenium-substituted acetylides and tetracyanoethylene (TCNE) in 1981 [14]. Later, metalfree substrates have also been employed in CA-RE reactions for the synthesis of structurally demanding push-pull chromophores by Diederich and co-workers [11]. The short and easy-to-perform CA-RE method has increased the variety in the design of the target push-pull chromophores. When the structures of push-pull chromophores obtained by CA-RE reactions are examined in detail, derivatization is mostly made in two main parts (donor groups and acceptor groups).

3-Alkynylindoles as Building Blocks for the Synthesis of Electronically Tunable Indole-Based Push–Pull Chromophores

“…Following the regioselective 3-iodination 1 was obtained in 74% yield. At the same time, alkynes substituted with electron-rich and electron-poor phenyl groups 2a – e , PAHs 2f – i , required for the synthesis of N -alkyl indole-based substrates 3a – i have also been synthesized using literature procedures. − With iodo-indole 1 and terminal alkynes 2a – i in hand, the Sonogashira cross-coupling step has been performed. While preparing disubstituted alkynes 3a , 3b , 3c , and 3e , cross-coupling reactions occurred at room temperature.…”

“…Commercially available chemicals were purchased, and no additional purification has been performed. Compounds 2a , 73 2b , 75 2d , 76 2e , 77 2f , 74 2g , 74 2h , 74 and 2i ( 78 ) were prepared according to literature procedures. Solvents (dichloromethane, hexanes, and ethyl acetate) used for extraction or column chromatography procedures were distilled.…”

Click-Type Synthesis of Homoconjugated Push–Pull Chromophores: Computational Investigation of Optical and Nonlinear Optical (NLO) Properties

“…ESP maps, one of the most frequently employed visualization techniques to describe electron transfer interactions in D-A systems, are also given in Table 1. [25][26][27] The regions shown in red represent the regions where the electron density increased after ICT and the regions shown in blue represent the regions where the electron density decreased. Accordingly, it is noticeable that the electron density is concentrated around the six membered ring, in line with the FMO results.…”

Synthesis, photophysical and nonlinear optical properties of push–pull tetrazoles

“…Organic push–pull molecules with a delocalized π-system exhibit highly efficient optoelectronic properties and show great promise as active components in the design of organic light-emitting diodes, 1 photodiodes, 2 solar cells 3 and nonlinear optical (NLO) devices. 4–6 Their unique spectroscopic properties are attributed to an intramolecular charge transfer (ICT) from the electron donating (D) to the electron accepting group (A) separated by a π-linker. 7 ICT generates a molecular dipole and polarization that imparts distinct electronic, linear and nonlinear optical properties to the molecule.…”