NIR‐Absorbing Donor–Acceptor Based 1,1,4,4‐Tetracyanobuta‐1,3‐Diene (TCBD)‐ and Cyclohexa‐2,5‐Diene‐1,4‐Ylidene‐Expanded TCBD‐Substituted Ferrocenyl Phenothiazines

Abstract

A series of unsymmetrical (D-A-D , D -π-D-A-D , and D -A -D-A -D ; A=acceptor, D=donor) and symmetrical (D -A-D-A-D ) phenothiazines (4 b, 4 c, 4 c', 5 b, 5 c, 5 d, 5 d', 5 e, 5 e', 5 f, and 5 f') were designed and synthesized by a [2+2] cycloaddition-electrocyclic ring-opening reaction of ferrocenyl-substituted phenothiazines with tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). The photophysical, electrochemical, and computational studies show a strong charge-transfer (CT) interaction in the phenothiazine derivatives that can be tuned by varying the number of TCNE/TCNQ acceptors. Phenothiazines 4 b, 4 c, 4 c', 5 b, 5 c, 5 d, 5 d', 5 e, 5 e', 5 f and 5 f' show redshifted absorption in the λ=400 to 900 nm region, as a result of a low HOMO-LUMO gap, which is supported by TD-DFT calculations. The electrochemical study exhibits reduction waves at low potential due to strong 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) and cyclohexa-2,5-diene-1,4-ylidene-expanded TCBD acceptors. The incorporation of cyclohexa-2,5-diene-1,4-ylidene-expanded TCBD stabilized the LUMO energy level to a greater extent than TCBD.

Tuning the Fluorescence and the Intramolecular Charge Transfer of Phenothiazine Dipolar and Quadrupolar Derivatives by Oxygen Functionalization

“…The PTZ unit is an electron-rich tricyclic heteroarene with nonplanar butterfly structure, characterized by the presence of powerful electron-donor sulfur and nitrogen atoms . In the literature, the photophysical properties and the HOMO–LUMO energy levels of PTZ derivatives have been easily modulated by substitutions at the nitrogen and the 3,7-positions of the phenothiazine unit. , Our group has functionalized the 3,7-positions of the phenothiazine unit by using polycyclic aromatic hydrocarbons of increasing complexity or strong acceptors such as benzothiadiazole or tetracyanobutadiene. , In the literature, push–pull phenothiazine–naphthalimide systems have been successfully employed in some optoelectronic applications. − However, the research on varying the oxidation state of the sulfur atom (sulfides, sulfoxides, and sulfones) in the thiazine ring of phenothiazine is still very limited. − In this study, we have synthesized new naphthalimide and phenothiazine-based systems, in which we have changed the oxidation state of the sulfur atom on the thiazine ring to investigate its effect on the photonic properties of the obtained materials.…”

Charge stabilization via electron exchange: excited charge separation in symmetric, central triphenylamine derived, dimethylaminophenyl–tetracyanobutadiene donor–acceptor conjugates

“…33 Tuning of the electronic and photonic properties of these systems can be achieved by modulating the design of donor or acceptor units and connecting p-spacer units. [34][35][36] Small organic p-conjugated donoracceptor systems exhibit a low band gap, intense absorption, and strong intramolecular interactions. 37,38 In several of these studies, triphenylamine, a classical nonplanar propeller shaped optoelectronic molecule, has been extensively used; extending their applications for developing eld effect transistors, sensors, and solid state uorescent and smart uorescent materials.…”

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

“…[20][21] It possesses unique electronic and optical properties. [22][23][24][25][26] The easy functionalization of phenothiazine chromophores and their higher chemical and thermal stability makes them an excellent prerequisite for optoelectronic applications. [27][28][29][30] On the other hand, the 1,8naphthalimide (NPI) is electron deficient fluorophore which acts as a strong acceptor.…”

“…Phenothiazine acts as a strong donor due to its electron rich nitrogen and sulphur atom [20–21] . It possesses unique electronic and optical properties [22–26] . The easy functionalization of phenothiazine chromophores and their higher chemical and thermal stability makes them an excellent prerequisite for optoelectronic applications [27–30] .…”