Solvent-Dependent Photophysics and Reactivity of Monomeric and Dimeric 4-Amino-1,8-Naphthalimides

Abstract

The solvent-dependent photophysics of two 4-amino-substituted 1,8-naphthalene imides (AIs) were studied using fluorescence spectroscopy and laser flash photolysis. The compounds were functionalized with water-soluble 2,2′(ethylenedioxy) diethylamine groups, yielding a monomer (AI3) and a dimer (AI4). The radiative and nonradiative singlet-state deactivation processes of AI3 and AI4 were quantified in 10 solvents and at different pH values. The fluorescence quantum yield for the AI4 dimer in water was more than 100× lower than in other solvents, or for the monomeric AI3. The enhanced nonradiative decay of aqueous solutions of dimeric AI4 is accompanied by biexponential decay kinetics, suggesting equilibration with a dark excited state. An oxygen-quenchable triplet state (T1) of AI3 was produced upon 416 nm excitation in both water and n-octanol. In water, the T1 state evolved into a long-lived transient that was unreactive toward oxygen or several electron donors. This species was not observed in n-octanol. The transient observed upon 416 nm excitation of AI4 in water was extremely weak. However, production of T1 in both AI3 and AI4 was evidenced by the photoinduced electron transfer to methyl viologen, albeit in low quantum yield (0.0503 and 0.00778 for AI3 and AI4, respectively). The photophysics and reactivity are consistent with the production of an intramolecular charge transfer (ICT) state that is stabilized in water. Significantly, this stabilization enhances nonradiative decay pathways, particularly in the AI4 dimer. The results indicate that the photochemistry of these compounds can be environmentally mediated, switching from radical- to triplet-initiated processes.

Creating a Natural Vascular Scaffold by Photochemical Treatment of the Extracellular Matrix for Vascular Applications

“…As described by Kelly et al [ 15 ], the 4-amino substituted 1, 8-naphthalimide core of 10-8-10 Dimer ( Figure 1 ) is proposed to undergo photoexcitation upon blue-light illumination (450 nm) to generate a transient singlet excited state, 1 [10-8-10]*, which converts via intersystem crossing (ISC) to a triplet excited-state intermediate, 3 [10-8-10]*, ( Figure 2 , Equation (I)). The triplet excited-state intermediate 3 [10-8-10]* can proceed to a water-stabilized and longer-lived intramolecular charge transfer (ICT) state, [10-8-10] •+ ( Figure 2 , Equation (II)).…”

“…Accordingly, the illumination of the 10-8-10 dimer could affect photosensitized oxidation and subsequent crosslinking reactions at oxidizable amino acid residues (e.g., tyrosine, tryptophan, histidine, methionine, cysteine) ( Figure 3 A). Mechanisms involving superoxide (O 2 •− , Figure 3 B) to affect H-atom abstraction have been described [ 15 , 16 , 17 ]. However, in polar, aqueous media, ICT state-promoted [10-8-10] •+ oxidation of amino acid residues cannot be ruled out ( Figure 3 C).…”

“…Decreasing the rate of restenosis should translate to higher long-term primary patency rates, and therefore, better patient mobility, reduced pain and improved quality of life. Systematic experiments were conducted to understand the photochemical mechanism of action of 10-8-10 Dimer when exposed to light at its absorption maximum [ 10 , 15 ]. These experiments support that the 4-amino substituted 1,8-naphthalimide core of the 10-8-10 Dimer undergoes photoexcitation upon illumination by a 450 nm light to generate a transient, reversible, excited state of the molecule ( Figure 2 and Figure 3 ).…”

Photosensitized Oxidative Dimerization at Tyrosine by a Water‐Soluble 4‐Amino‐1,8‐naphthalimide

“…The photoexcited tripletstate of 1 (Eq. 1, 3 PS*) is capable of reducing methyl viologen by a PET process, [19] thus it is feasible that 1 can promote the formation of reactive oxygen species (ROS) and induce amino acid residue oxidation by a type I or II photosensitized oxidation mechanism. [47] Indeed, the one-electron reduction potential of molecular oxygen ( 3 O 2 ) is more positive than that of methyl viologen (E(O 2 /O 2 *À )) = À 0.16 V vs. NHE), [48] thus, the formation of superoxide (O 2 *À ) via quenching of the photoexcited tripletstate of 1 (Figure 3A) represents a plausible initiation event for the oxidation of Tyr residues (Figure 3B).…”

“…[15][16][17][18] imides, such as dimer 1 (Figure 2). [19] Both the water-soluble dimer (1) and a monomeric analog (not shown), produce reactive transients (Eq. 1, PS = photosensitizer) upon excitation with 416-nm light in phosphate buffer at pH = 7.4.…”