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

Abstract

In this study, two different classes of push–pull chromophores were synthesized in modest to excellent yields by formal [2+2] cycloaddition-retroelectrocyclization (CA-RE) reactions. N -Methyl indole was introduced as a new donor group to activate alkynes in the CA-RE transformations. Depending on the side groups’ size and donor/acceptor characteristics, N -methyl indole-containing compounds exhibited λ max values ranging between 378 and 658 nm. The optoelectronic properties of the reported D–A-type structures were studied by UV/vis spectroscopy and computational studies. The complete regioselectivity observed in the products was elaborated by one-dimensional (1D) and two-dimensional (2D) NMR studies, and the electron donor strength order of N -alkyl indole and triazene donor groups was also established. The intramolecular charge-transfer characteristics of the target push–pull chromophores were investigated by frontier orbital depictions, electrostatic potential maps, and time-dependent density functional theory calculations. Overall, the computational and experimental results match each other. Integrating a new donor group, N -alkyl indole, into the substrates used in formal [2+2] cycloaddition-retroelectrocyclizations has significant potential to overcome the limited donor-substituted substrate scope problem of CA-RE reactions.

Phenothiazine and phenothiazine-5,5-dioxide-based push–pull derivatives: synthesis, photophysical, electrochemical and computational studies

“…S10 in the ESI†). 6 The push–pull chromophores PTZ 4–6 were synthesized by the oxidation reaction of PTZ 1–3 with 3 equivalents of 3-chloroperbenzoic acid ( m -CPBA) in dry DCM solvent at room temperature for 1 h, which resulted in PTZ 4–6 in 80%, 75%, and 79% yield, respectively (Scheme 1).…”

“…The longer wavelength transition is associated with intramolecular charge transfer (ICT) from the donor phenothiazine to acceptor TCBD unit. 6,50,52,53 Similarly, the cyclohexa-2,5diene-1,4-diylidene-expanded TCBD substituted PTZ 3 and phenothiazine-5,5-dioxide functionalized cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD substituted PTZ 6 exhibit two strong absorption bands at 400 nm, 675 nm and 373 nm, 535 nm, respectively. The TCBD and cyclohexa-2,5-diene-1,4diylidene-expanded TCBD functionalized PTZ 2 and 3 exhibit absorption bands at a higher wavelength region than PTZ 5 and 6, reflecting the weak donor ability of the phenothiazine-5,5dioxide unit.…”

“…Over the last few decades, the development and study of organic p-conjugated push-pull materials has become an attractive field of research due to wide applications in organic light-emitting diodes (OLEDs), organic photovoltaics, nonlinear optics, field-effect transistors (OFET), organic photodetectors and bioimaging. [1][2][3][4][5][6][7][8] These donor-acceptor (D-A) derivatives exhibit unique photonic properties and that can be improved by simple synthetic changes. 9,10 In these p-conjugated chromophores, the heteroatom-containing cyclic systems were primarily used to tune the photophysical and redox properties of push-pull dyes.…”

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.…”

π-Bridge Extension and Additive-Influenced Panchromaticity: A Synergetic Ploy for Augmenting Photovoltaic Characteristics of π-Distorted Chromophores

“…Seminal contributions in this field were made by Jen, Bosshard (1999), and Yamashita (2004). − Later in 2005, it was Diederich who elaborated the scope to diverse substrates and studied the structural influence on the reactivity as well as chemical yields . From then onward, continuing development by the same group along with others paved the way for the discovery of numerous molecular chromophores by adopting this chemistry. − As TCBD/DCNQ-containing products possess distinct photophysical, electrochemical, and structural properties, they have gained significant momentum in materials science as well as optoelectronics. − Among the different applications, the light harvesting property of TCBD/DCNQ-derived π-semiconductors has received profound interest in the area of organic photovoltaics (OPVs). − …”