Solid‐State Fluorescence of Excited‐State Cation–Anion Intermolecular Proton Transfer in 2‐(2‐Hydroxypyridyl)benzothiazole. Issue 11 (5th April 2022)

• Record Type: Journal Article
• Authors: Takahashi, Keigo; Sambe, Kohei; Kasahara, Yotaro; Takeda, Takashi; Hoshino, Norihisa; Sakai, Ken‐ichi; Akutagawa, Tomoyuki
• Is Part Of: Advanced optical materials. Volume 10:Issue 11(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-04-05
• Subjects: dielectrics -- excited‐state intramolecular proton transfer -- fluorescence -- hydrogen‐bonds -- sensing; Optical materials -- Periodicals; Photonics -- Periodicals; 620.11295
• DOI: 10.1002/adom.202200134
• Languages: English
• ISSNs: 2195-1071

Abstract

Abstract: A basic pyridyl unit is introduced to the excited‐state intramolecular proton transfer (ESIPT) of 2‐(2‐hydroxyphenyl)benzothiazole fluorescent molecule, forming 2‐(2‐hydroxypyridyl)benzothiazole (1 ). The formation of the proton‐transferred H1 + X − salts is confirmed in X − = Cl −, Br −, BF4 −, and CF3 COO − (trifluoroacetate, TFA − ) wherein the highly acidic HX species are easily transferred to the pyridyl unit of 1 . Normal ESIPT fluorescence is observed in H1 + BF4 − crystals as the ESIPT active intramolecular O−HN= hydrogen‐bonding conformation (Stokes shift ≈ 8500 cm −1 ). In contrast, the H1 + Cl −, H1 − Br −, and H1 + TFA − salts exhibit an ESIPT inert structure without any intramolecular O−HN= hydrogen‐bonding structure (Stokes shift ≈ 9500 cm −1 ), which could not be sufficiently explained by normal ESIPT fluorescence. The excited‐state monoprotonated H1 + exhibits an intermolecular cation–anion proton transfer from N−H + X − to NHX, which transforms the cationic H1 + to neutral 1, and exhibits intense green fluorescence with a large Stokes shift. Abstract : A basic pyridyl unit is introduced to the excited‐state intramolecular proton transfer of 2‐(2‐hydroxyphenyl)benzothiazole fluorescent molecule. The excited‐state monoprotonated species exhibit an intermolecular cation–anion proton transfer from N−H + X − to NHX, which transforms the cationic to neutral states, and exhibit intense green fluorescence with a large Stokes shift.