pH‐Dependent Excited‐State Properties of N,N‐di(2‐phosphonoethyl)‐1,4,5,8‐naphthalenediimide

Abstract

ABSTRACTings open the horizons for the use of these imides in pho-The effect of the protonation state of a novel aqueous soluble N, N '-di(2-phosphonoethyI)-1,4,5,8-naphthaIenediimide (DPN) on its spectroscopic properties is studied. In aqueous solution DPN depicts linear Lambert-Beer plots up to the solubility limits at pH 1.0, 7.1 and 10.1, in accordance with its solubilization as a monomer. A small increase in the extinction coefficients with pH is observed. Conversely a strong decrease in the fluorescence emission yields are observed with the increase in pH. These results are shown to originate from the distinct efficiencies of the intersystem crossing of DPN as a function of the net charge on the phosphono moieties. Accordingly, from the decrease in fluorescence emission, titration curves were obtained resulting in two pKa of -1.5 and 6.7 in agreement with the potentiometric analysis. In parallel monitoring the amount of heat deposited in the system shows an inverse pattern, that is, increase in the thermal lensing time-resolved signal with pH. Laser flash photolysis and thermal lensing data in the absence and presence of oxygen show the interplay of an intersystem crossing process with the protonation state of the dye. The changes in protonation from neutral to two-and four-fold charged species are accompanied by an enhancing effect on the naphthalenediimide ring toward spin inversion (triplet formation) and consequently in different fluorescence yields.

Synthesis and Characterization of Silica Gel Particles Functionalized with Bioactive Materials

“…The addition of a new Zr layer leads to DPN immobilization resulting in the broadening of the spectrum observed with aggregated DPN (Fig. 4, trace c; Rodrigues et al, 1999). The spectra of silica gel with Trp or tripeptide (traces e and d respectively) are similar to that of immobilized DPN and shows an extra transition at ∼280 nm due to Trp.…”

“…4. The spectrum of DPN free in aqueous media (trace a) shows its usual vibronic aspect with maxima at ∼380, 360, 335, and 325 nm (Rodrigues et al, 1999). The spectrum of DPN with one extremity bound to silica particles and another free (Fig.…”

“…Transient signals due to Scheme 1. 3 DPN and to DPN .− are observed at 450 and 475 nm, respectively (Rodrigues et al, 1999;Aveline et al, 1997). For clarity purpose the transient signals of a longer lived NDI derivative (a N-dibutyl-naphthalenediimide DBN, up right panel) dissolved in a rigid matrix (sucrose octaacetate) and of DPN in water using a good electron donor (1,4-diaza-biciclo [2.2.2] octano, DABCO) are included.…”

“…N,N -bis (2-phosphnooethyl)-1,4,5,8-naphthalenediimide (DPN) and N,N -bis(dibutyl)-1, 4, 5, 8-naphthalenediimide (DBN) were prepared as previously described (Rodrigues et al, 1999). Fmoc-Ala-OH, Fmoc-Trp-OH1, 3-diisopropylcarbodiimide (DIC), 1-hydroxybenzotriazole (HOBt) and piperidine were Aldrich products.…”

“…The photoactive chromophore group is a naphthalenediimide (NDI) derivative due to its straightforward synthetic chemistry and to its favorable photochemical properties (Rodrigues et al, 1999;Aveline et al, 1997) Excitation of NDI produces an extensive amount of triplet state due to a high yield intersystem crossing (Rogers and Kelly, 1999), as well as radical species in the presence of appropriate electron donors.…”