Complexes of a naphthalimide photoacid with organic bases, and their excited-state dynamics in polar aprotic organic solvents

Abstract

Complex formation and intermolecular excited-state proton transfer (ESPT) between a dihydroxy-1,8-naphthalimide photoacid and organic bases are investigated in polar aprotic solvents. First, quantum chemical calculations are used to explore the acid-base and spectroscopic properties and to identify energetically favorable complexes. The two hydroxyl groups of the photoacid enable stepwise formation of 1 : 1 and 1 : 2 complexes. Weak bases exhibit only hydrogen-bonding interactions whereas strong bases are able to deprotonate one of the hydroxyl groups resulting in strong negative cooperativity (K1≫ 4K2) in the formation of the 1 : 2 complex. Time-resolved fluorescence studies of the complexes provide strong indications of a three-step dissociation process. The species involved in the model are: a hydrogen-bonded complex, a hydrogen-bonded ion pair, a solvent separated ion pair, and a free ion pair.

Modulation of Excited‐State Proton‐Transfer Dynamics inside the Nanocavity of Microheterogeneous Systems: Microenvironment‐Sensitive Förster Energy Transfer to Riboflavin

“…Thus, we expected that any change in the microenvironment, in terms of polarity, hydrogen bonding, viscosity, etc., will have a strong influence on their emission properties. For example, the polar solvents preferentially stabilize the anionic form, as the latter possesses larger charge separation compared to the neutral form (Figure b & S2b) . However, a dramatic change was observed in alcoholic solvents, which cannot be explained on the basis of polarity alone.…”

“…For example, the polar solvents preferentially stabilize the anionic form, as the latter possesses larger charge separation compared to the neutral form ( Figure 2b & S2b). [14] However, a dramatic change was observed in alcoholic solvents, which cannot be explained on the basis of polarity alone. This change is presumably caused by hydrogen bonding interaction between TDMPP and the solvent molecules in the excited state, which ultimately accelerates the proton transfer process (Figure 2c).…”

Propyl acetate/butyronitrile mixture is ideally suited for investigating the effect of dielectric stabilization on (photo)chemical reactions

“…On the other hand, a strong base (DBU) will deprotonate one of the hydroxyl groups already in the ground state. 44 Therefore, the impact of dielectric stabilization on the deprotonation constant can be demonstrated in the presence of a strong base.…”

“…For this purpose, we use a 1,8-naphthalimide-based photoacid (Chart 1) complexed with either a weak base (N-methylimidazole, NMI) or deprotonated by a strong base (1,8-diazabicyclo[5.4.0]undec-7-ene, DBU). 43,44 Experimental section…”

Excited-state proton transfer of 4-hydroxyl-1, 8-naphthalimide derivatives: A combined experimental and theoretical investigation

“…© 2016. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/Recently, Brouwer and coworkers synthesized and characterized some hydroxy-substituted 1, 8-naphthalimide derived "super" photoacids, where the hydroxyl group is located at the 3 or 6 position of the naphthalimide ring [6,14]. However, for 4-hydroxyl-1, 8-naphthalimide derivatives, which are extensively used for designing turn-on or rationmetric fluorescent indicators for bioimaging [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29], the photophysical properties and the excited-state proton transfer (ESPT) reactions are rarely studied [30].In this contribution, the steady-state absorption and emission spectra of two 4-hydroxyl-1, 8-naphthalimide derivatives (BOH and MOH, Scheme 1) in organic solvents and water with various pH values are recorded.…”