Abstract
A dipolar dipicolinate derivative, trans-dimethyl-4-[4′-(N,N-diphenylamino)-styry1]-pyridin-2,6-dicarboxylate (P-1), and a P-1based V-shaped compound, {4-[(E)-2-(2,6-dimethoxycarbonylpyridin-4-yl) vinyl]}-N-phenyl-N-{4-[(E)-2-(2,6-dimethoxycarbonylpyridin-4-yl)vinylphenyl]}aniline (P-2), with intense two-photon fluorescence emission properties were systematically investigated by using steady-state absorption and fluorescence spectroscopy, open-aperture Z-scans, and two-photon excited fluorescence (TPF). The two-photon absorption cross-section of the V-shaped compound P-2 in tetrahydrofuran (THF) was determined to be 208 GM, which represents a 6.5-fold enhancement compared with its dipolar counterpart P-1 (32 GM). Extension of the intramolecular charge transfer (ICT) in the V-shaped dipicolinate derivative has been suggested as the mechanism of enhancement. The excited state dynamics from transient absorption spectroscopy were analyzed and discussed. The formation and relaxation lifetimes of the ICT state for these dipicolinate derivatives in THF solutions were found to be several picoseconds and several hundred picoseconds, respectively. The results show an increased ICT character of the V-shaped compound and a potential application for this compound in two-photon fluorescence imaging fields.
Highlights
INTRODUCTIONSmall focal volume (on the order of approximately λ3), which permits three-dimensional image resolution.[6] Based on these advantages, two-photon labels with strong twophoton excited fluorescence (TPF) are highly desirable for biological applications and, subsequently, have attracted increased interest in recent years.[7] Labels that contain both a large two-photon absorption (TPA) cross section and a high fluorescence quantum yield are desired.[8] a lot of effort has been made to improve both the Two-photon absorption (TPA) cross section and the fluorescence quantum yield
Two-photon absorption (TPA) is a third-order nonlinear optical process that requires two photons to interact simultaneously with a single molecule.[1]
twophoton excited fluorescence (TPF) has been found to be a powerful tool in the field of laser scanning fluorescence microscopy imaging and is frequently employed in fluorescent dyes used as molecular probes.[2,3,4,5]
Summary
Small focal volume (on the order of approximately λ3), which permits three-dimensional image resolution.[6] Based on these advantages, two-photon labels with strong TPF are highly desirable for biological applications and, subsequently, have attracted increased interest in recent years.[7] Labels that contain both a large two-photon absorption (TPA) cross section and a high fluorescence quantum yield are desired.[8] a lot of effort has been made to improve both the TPA cross section and the fluorescence quantum yield To this end, many dipolar, quadrupolar, octupolar, multi-branched chromophores and macrocyclic molecules have been designed and investigated.[9,10,11,12,13,14,15,16] there are few reports of coordinating TPA compounds with metal ions in an effort to improve the TPA response, the mechanical properties and the stability of the materials in an ambient environment. Our study demonstrates that the V-shaped compound P-2 based on dipicolinate hold promise for biological fluorescence imaging for life sciences fields, and can be used to trace interactions in living cells, such as those between DNA and proteins.[25,26]
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