Bright, emission tunable fluorescent dyes based on imidazole and π-expanded imidazole

Abstract

A diverse set of imidazole-and p-expanded imidazole derivatives displaying excited state intramolecular proton transfer (ESIPT) was designed and synthesized. The effect of structural variation on photophysical properties was studied in detail for nine dyes. The relationship between the structure and photophysical properties was thoroughly elucidated also by comparing with analogues with blocked ESIPT functionality. All but one of the obtained compounds exhibit ESIPT, as demonstrated by large Stokes shifts (6500-15 600 cm À1 ). The type of p-expansion strongly influences the overall optical phenomena: while typical p-expansion preserves ESIPT activity, the direct fusion of imidazole with a naphthalene unit at positions 4 and 5 results in dyes which do not exhibit ESIPT. The compound possessing an acidic NH group as part of an intramolecular hydrogen bond system has a much higher fluorescence quantum yield and Stokes shift than its analogue bearing an OH group. The occurrence of ESIPT for tosylamide analogues is less affected by the hydrogen-bonding ability of the solvents compared to the unprotected amines. Two-photon absorption cross-sections of the selected derivatives are in the range of 5-100 GM.

On the Fine‐Tuning of the Excited‐State Intramolecular Proton Transfer (ESIPT) Process in 2‐(2′‐Hydroxybenzofuran)benzazole (HBBX) Dyes

“…[3] Therefore, ESIPT emission is characterized by enhancedS tokess hifts as compared with regularf luorophores, and as trong dependence of the proton-transfer strength and fluorescencei ntensity on the environment.T his is especially remarkable in the case of protic media, which can induce ap artialf rustrationo ft he protont ransfert hrough ah ydrogen-bonded stabilization of the enol speciesi nt he most commonc ase, that is, of an ESIPT process that consistso fa nenol/keto tautomerization. Of these structures, one can quote reported ESIPT emitters based on 2,2'-bipyridine-diol, [5] benzoimidazol indolizines, [6] imidazoles, [7] hydroxytriazine, [8] imidazo [1,2-a]pyridine, [9] or benzoquinoline, [10] among other derivatives. [4] The ESIPT process has been revealed in both natural and synthetic chromophoric structures that featureastrong hydrogen bond in the grounds tate in their p-conjugated molecular core.…”

How To Reach Intense Luminescence for Compounds Capable of Excited‐State Intramolecular Proton Transfer?

“…[e] 2‐(1,4,5‐Triphenyl‐1 H ‐imidazol‐2‐yl)phenol . [f] 2‐(1‐Phenyl‐1 H ‐phenanthro[9,10‐ d ]imidazol‐2‐yl)phenol …”

“…The most important feature of all ESIPT‐capable compounds with rigid ring structures, namely, 6 a – d , 11 , and 12 (Figures and ), is their strong fluorescence, regardless of the polarity of the media, that is, they manifest large fluorescence quantum yields not only for nonpolar, but also for polar, solvents. The latter is indeed a crucial finding because an increase in solvent polarity tends to drastically decrease the fluorescence quantum yields of ESIPT‐capable compounds with protic groups on nonfused aromatic rings …”

A highly sensitive benzimidazole-based chemosensor for the colorimetric detection of Fe(ii) and Fe(iii) and the fluorometric detection of Zn(ii) in aqueous media

“…[32][33][34] Thus, low cost and easily prepared Zn 2+ uorescence chemosensors are needed for convenience. [43][44][45] Also, 4-diethylaminosalicylaldehyde moiety is a well-known uorophore and many chemosensors with this moiety are water-soluble. [43][44][45] Also, 4-diethylaminosalicylaldehyde moiety is a well-known uorophore and many chemosensors with this moiety are water-soluble.…”