Expansion of Photostable Luminescent Radicals by Meta‐Substitution

Abstract

Polychlorinated pyridyldiphenylmethyl radicals having substituents meta to the position bearing the carbon‐centered radical (α‐carbon) are synthesized. All of them are stable in ambient conditions in solutions and fluorescent in cyclohexane. The fluorescence of the radicals with bromo, phenyl, 4‐chlorophenyl, or 2‐pyridyl substituents are enhanced in chloroform, while the emission of the radicals with 2‐thienyl or 2‐furyl substituents are quenched in chloroform. DFT and TD‐DFT calculations indicate that the first doublet excited states of the former are locally excited, while the first doublet excited states of the latter are charge transfer states from the π‐electron‐donating substituent to the accepting radical. The latter also show much higher photostability under 370‐nm light irradiation compared with the first reported photostable fluorescent radical, (3,5‐dichloro‐4‐pyridyl)bis(2,4,6‐trichlorophenyl)methyl radical (PyBTM), with pronounced bathochromic shifts of the fluorescence.

2,7‐Substituted N‐Carbazole Donors on Tris(2,4,6‐trichlorophenyl)methyl Radicals with High Quantum Yield

“…Many of the reported compounds exhibit reasonable quantum yields; however, the emission profile of all radicals reported so far remains in the red to deep‐red spectrum. [ 11,23–27 ] For TTM‐Cz functionalized with electron withdrawing nitriles in the 3,6 and 2,7‐position of Cz, a hypsochromic shift of the photoluminescence into the green spectrum has been predicted using quantum mechanical calculations. [ 21,28 ] Yet, Cz‐TTMs with electron withdrawing groups in the 2,7‐position have not been synthesized to date.…”

Enhancement of fluorescence and photostability of luminescent radicals by quadruple addition of phenyl groups

“…The precursor of Ph 4 -F 2 PyBTM ( 1 ): αH-Ph 4 -F 2 PyBTM ( 1H ) was synthesized by Suzuki–Miyaura coupling between phenylboronic acid and (3,5-difluoro-4-pyridyl)bis(3-bromo-2,4,6-trichlorophenyl)methane (αH- m Br 2 -F 2 PyBTM), the compound we previously used to prepare m Ph 2 -F 2 PyBTM by Migita–Kosugi–Stille coupling. 10 Probably two bromine atoms at the meta -positions were first substituted and then two chlorine atoms at para -positions were substituted by phenyl groups. The substitution at adjacent bromo and chloro groups show the powerful nature of this reaction.…”

Electro-optical π-radicals: design advances, applications and future perspectives

“…99 Switching PyBTM nitrogen atom from para - to meta -position generally enhances the solid-state emission even at room temperature (see structure S8 , Scheme S1 and Table S1, ESI†). 100 Hattori et al 101 coupled different aryl substituents to the meta -positions of PyBTM. Electron-rich thiophene and furan rings changed the localised electronic structure of PyBTM into D–A type systems whose photostabilities were enhanced, albeit with concomitant emission quenching effects (structures S9 and S10 , respectively, Scheme S1 and Table S1, ESI†).…”