Synthesis and Evaluation of a 1,3a,6a‐Triazapentalene (TAP)‐Bonded System

Abstract

A method of synthesizing a directly connected 1,3a,6a‐triazapentalene (TAP) ring system as a linearly bonded aromatic system with a planar form was established. Various TAP‐dimers and a 2‐alkyl‐TAP‐trimer were synthesized and their fluorescence properties were evaluated. Although the direct connection of the TAP ring with other TAP rings did not affect the fluorescence properties in diluted solvent, TAP‐dimers showed unique fluorescence properties derived from the aggregation state under highly concentrated conditions. In particular, TAP‐dimer 5 f showed aggregation‐induced emission in highly concentrated solution, and 5 b showed typical mechanochromic fluorescence in the solid state despite their compact molecular size.

Development of a 1,3a,6a-triazapentalene derivative as a compact and thiol-specific fluorescent labeling reagent

“…We recently discovered that a 1,3a,6a-triazapentalene (TAP) (1) skeleton is a compact and highly fluorescent chromophore with the potential to overcome the molecular size problem (Fig. 2) 15 , and it has been applied to various fluorescent probes [16][17][18][19] . Interestingly, the fluorescence of the TAPs shifted to longer wavelengths along with the inductive effect of the 2substituents 15,[19][20][21][22][23][24] .…”

Pyridazino-1,3a,6a-Triazapentalenes as Versatile Fluorescent Probes: Impact of Their Post-Functionalization and Application for Cellular Imaging

“…Therefore, extensive synthetic studies have been reported on the 5/5 bicyclic scaffold in order to introduce structural diversities in order to improve its fluorescent property and/or its chemical stability [ 8 ]. However, the postfunctionalization remains delicate and thus the modulation of the existing TAP fluorophore is closely related to the few synthetic pathways reported in the literature ( Scheme 1 ), i.e., substitution at position 2 and 4 [ 9 ], at position 2 [ 10 ], position 2 and 5 [ 11 , 12 ], at position 4 [ 13 ], at position 2, 6 [ 14 ], at position 3 [ 15 , 16 ] and at position 2, 3, 4 and 6 [ 17 ]. Recently, the development of a TAP system flanked with an additional fused heteroaromatic ring demonstrated a significant improvement in respect to the chemical stability while retaining promising spectroscopic properties [ 18 , 19 ].…”

Synthesis, Photophysical Properties, and Aromaticity of Pyrazine-Fused Tetrazapentalenes

“…For instance, the 1,3a,6a-triazapentalene (TAP) is a zwitterionic aromatic heterocycle with three consecutive nitrogen atoms of which two are at the bicyclic ring junction. The intramolecular charge transfer that can occur in this family of compounds has been particularly studied to produce compact organic fluorophores, either as simple bicyclic systems − or as larger molecules when the azapentalene bicyclic system is fused to various heterocyclic scaffolds (Scheme a). − They possess an amphiphilic character particularly interesting for biological imaging applications. − With an additional nitrogen atom, zwitterionic tetraazapentalene analogue (TeAP) remains more confidential and were developed for energetic applications. − Among them, z-TACOT and derivatives exhibit a unique pattern with four consecutive nitrogen atoms arranged in a Z shape, which was even recently flanked with various energy-rich fragments such as benzofuroxan or 1,2,3,4-tetrazine 1,3-dioxane. − …”