Tuning Electron‐Withdrawing Strength on Phenothiazine Derivatives: Achieving 100 % Photoluminescence Quantum Yield by NO₂Substitution

Abstract

The weak fluorescence( quantum yield < 1% in cyclohexane)o fp henothiazine (PTZ)i mpedes its further application. In addition, the nitro group (NO 2 )i sawell-known fluorescence quencher.I nterestingly,w eo btained ah ighly fluorescent chromophore by combining these two moieties, forming 3-nitrophenothiazine (PTZ-NO 2 ). For comparison, a series of PTZ derivatives bearing electron-withdrawing groups (EWGs;C Na nd CHO) or electron-donating groups (EDGs;O Me) at the 3-position have been designed and synthesized. The phenothiazines bearing EWGs exhibited enhanced emission compared with the parent PTZ or EDGd e-rivatives. Computational approaches unveiled thatf or PTZ and PTZ-OMe,t he transitions are from HOMOs dominated by p orbitals to LUMOso fm ixed sulfur nonbonding-p*o rbitals, and hence are partially forbidden. In contrast, the EWGs lower the energy level of the lone-pair electrons on the sulfur atom, thereby suppressing the mixingo ft he nonbondingo rbital with the p*o rbital in the LUMO, such that the allowed pp*t ransition becomes dominant. This work thus demonstrates aj udiciousc hemical design to fine-tune the transition character in PTZ analogues,w ith PTZ-NO 2 attaining 100 %e mission quantumy ields in nonpolar solvent.

Deciphering the unusual fluorescence in weakly coupled bis-nitro-pyrrolo[3,2-b]pyrroles

“…2 and 3b, c). This pronounced solvatofluorochromism is consistent with the breaking of the quadrupolar symmetry of the FC LE states leading to dipolar S 1 states capable of radiative deactivation 37,[52][53][54][55][56] .…”

Fluorescent Chromophores Containing the Nitro Group: Relatively Unexplored Emissive Properties

“…Recent work by Chen et al. introduced the nitro group on the C‐3 substituted phenothiazines ( PTZ ), [62] a well‐known electron donating moiety applied in optoelectronics, especially in the thermally activated delayed fluorescence (TADF) [63] for organic light emitting diodes (OLEDs) [64] (see Figure 17), well extended the corresponding photophysics. In this work, the most interesting part is that the PTZ derivatives 3‐nitrophenothiazine ( PTZ − NO 2 ) exhibits 100 % PLQY in cyclohexane, showing the brilliant photophysical behavior.…”

“… Excited‐state optimized HOMO and LUMO orbitals of the molecules computed by m062×/6‐31+g(d,p) with cyclohexane as solvent from Chen et al.’s work in 2020 [62] …”

Structure-induced optoelectronic properties of phenothiazine-based materials

“…its low photoluminescence quantum yield (PLQY) in nonpolar solvents (o1% in cyclohexane). 33 In particular, a highly fluorescent PTZ-based derivative, namely 3-nitrophenothiazine, was achieved with the modification of PTZ with a nitro group (NO 2 ) at the para position with respect to the N atom of the PTZ structure. NO 2 -modified PTZ chromophore displayed a 100% PLQY in cyclohexane.…”

“…62 Fig. 9 Phenothiazine (PTZ)-based donor (32)(33)(34)(35)(36)(37)(38) and acceptor (39-43) materials. The key properties of OSCs employing these dyes in the BHJ blend are listed in Table 1.…”