Bright, emission tunable fluorescent dyes based on imidazole and π-expanded imidazole
作者:Kamil Skonieczny、Adina I. Ciuciu、Eva M. Nichols、Vincent Hugues、Mireille Blanchard-Desce、Lucia Flamigni、Daniel T. Gryko
DOI:10.1039/c2jm33891b
日期:——
A diverse set of imidazole- and Ï-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 (6500â15â600 cmâ1). The type of Ï-expansion strongly influences the overall optical phenomena: while typical Ï-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 5â100 GM.
Blue-green emitting sulphonamido-imidazole derivatives: ESIPT based excited state dynamics
作者:Adina I. Ciuciu、Lucia Flamigni、Kamil Skonieczny、Daniel T. Gryko
DOI:10.1039/c3cp52291a
日期:——
Six imidazole derivatives characterized by the presence in their molecules of a sulphonamido group and able to display excited state intramolecular proton transfer (ESIPT) have been synthesized in a straightforward manner and the dynamics of their excited states investigated in detail in solvents of different polarity and proticity: toluene (TOL), dichloromethane (DCM) and methanol (MeOH). With the exception of one compound, these ESIPT-capable molecules are highly luminescent. The major emitting species at room temperature is the ketimine (K) tautomer but the weak emission from the enamide (E) form was detected in several cases. In general, the luminescence quantum yields (ϕfl) of the K form range between 0.4 and 0.6 with lifetimes of several nanoseconds, with radiative rate constants kr of the order of 108 s−1. The lifetime of the E form, and hence of the ESIPT process, range between τ <10 ps up to 190 ps. At 77 K, in addition to hypsochromically shifted fluorescence bands from the E and/or K tautomers, E phosphorescence emissions with lifetimes in the range of seconds (0.4–2.5 s) are also detected. The triplet excited state absorbance of these molecules was probed in DCM and MeOH and both E (between 450–520 nm) and K (at about 420 nm) forms were identified. The triplet lifetimes at room temperature in air-free solutions are in the microsecond range, whereas the reaction rates with oxygen are of the order of 109 M−1 s−1.