Donor‐Acceptor Based 1,8‐Naphthalimide Substituted Phenothiazines: Tuning of HOMO‐LUMO Gap

Abstract

A set of donor-acceptor (D-A) substituted phenothiazine based chromophores (D-π-D-π-A, D'-π-D-π-A, D-A'-D-π-A and D'-A'-D-π-A) were designed and synthesized. The phenothiazine was substituted with the 4-ethynyl-1,8-naphthalimide (NPI) on one side and a variety of donors (phenothiazine, carbazole, ferrocene and triphenylamine) were introduced on the other side of phenothiazine via Pdcatalyzed Sonogashira cross-coupling reaction resulting PTZ8-11. In order to tune the optoelectronic properties of the phenothiazine chromophores, cyano-based acceptor 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) was incorporated by [2 + 2] cycloaddition-electrocyclic ring-opening reaction of phenothiazine derivatives PTZs 8-11 and tetracyanoethylene (TCNE). The photophysical and electrochemical studies showed that the incorporation of TCBD acceptor in the phenothiazine chromophores PTZs 12-15 facilitated the donor-acceptor strength to greater extent. The electronic absorption spectra exhibited red shifted absorption bands for the TCBD substituted phenothiazines as compared to the alkynylated phenothiazines which led to much lower optical band gaps in the formers. The experimental values were also supported by the DFT and TD-DFT calculations.

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

“… 46 Similarly, long-term storage limitations and instability reduce the diversity of donor-substituted alkynes used in CA-RE. Metal acetylides, 19 , 47 dialkylaniline, 20 ferrocene, 23 thiophene, 48 p-methoxybenzene, 48 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY), 49 cyclopenta[ b ]furan-2-one, 50 metalloporphyrins, 51 carbazole-substituted alkynes, 52 ynamides, 53 tetrathiafulvalene, 17 azulene, 54 phenothiazine, 55 triazene, 56 , 57 and ureas 33 are donor substrates displaying sufficient reactivity in CA-RE reactions with TCNE. Surprisingly, the donor substrate scope (dialkylaniline, 42 ferrocene, 58 cyclopenta[ b ]furan-2-one, 59 carbazole, 60 metal acetylides, 61 azulene, 62 phenothiazine, 63 thiophene 64 ) is much more limited in CA-RE reactions with TCNQ ( Figure 1 ).…”