Changes in Emission Properties by π‐Stacking and Conformation Adjustment of an Imidazole‐Tethered Naphthalimide Derivative

Abstract

Solid state self-assemblies of 2,4-dinitrophenolate, 2,4,6-trinitrophenolate salts of N-(3-imidazol-1-yl-propyl)-1,8-naphthalimide (abbreviated as imidanap) have distinguishable p-stacking patterns, each stack influences fluorescence emission causing fluorescence quenching. It is found that the solid sample of nitrate or bromide salt of imidanap retains fluorescence properties of the parent compound. Photo-induced electron transfer process in solution gets prominence upon interactions of imidanap with hydrobromic as well as nitric acid but in the nitrophenolate salts the effect of p-interactions over-ride the effect of protonation of imidazole to change intensity of fluorescence emission. DFT calculations using B3LYP functional with 6-31 + G (d,p) as basis set have revealed LUMO in the imidanap and in the respective nitrophenolate salts are localized on the naphthalimide unit whereas HOMO in each case is localization differently over the rings other than the naphthalimide ring. Studies based on 1 H NMR suggest that water causes conformation adjustments of imidanap by forming hydrogen bonds. This enhances photo-induced electron transfer (PET) emission of the imidanap until a limiting concentration of water is reached, beyond which increase in amount of water causes quenching of emission. The PET-ON state of imidanap generated by addition of water to an acetonitrile solution is quenched by 2,4,6-trinitrophenol due to charge-transfer interactions.

Phenanthridine-pyrene conjugates as fluorescent probes for DNA/RNA and an inactive mutant of dipeptidyl peptidase enzyme

“…Further, although interaction of pyrene and phenanthridine is necessary for FRET, it seems that higher degree of aromatic surfaces overlapping and cation-π interactions also yield excimer fluorescence quenching [22,[24][25]. This conclusion is strongly in line with experimental insight reported here and helps in explaining the observed excimer fluorescence quenching with a decrease in the solution pH value as well as with the stronger excimer fluorescence of Phen-Py-1 compared to Phen-Py-2.…”

Photophysical Properties of Phthalimide and Pyromellitic Diimide Tethered Imidazolium Nitrophenolate Salts

“…The water molecules competes to set apart the ion pairs, hence the recovery of emission from the salt upon addition of water was possible. In a recent report, we observed that addition of water to analogous naphthalimide derivative N‐(3‐imidazol‐1‐yl‐propyl)‐1,8‐naphthalimide has shown enhancement of emission up to a particular concentration; whereas the emission quenching of the N‐(3‐imidazol‐1‐yl‐propyl)‐1,8‐naphthalimide with addition of water took place . In the present examples, only the quenching of emission were observed upon addition of water.…”

“…The emission of each compound L 1 or L 2 were quenched by H24dnp and H246tnp in a similar manner to the reported quenching of fluorescence of the N‐(3‐imidazol‐1‐yl‐propyl)‐1,8‐naphthalimide and N,N′‐ bis (3‐imidazol‐1‐yl‐propyl)naphthalenediimide . Hence, for a comparison the normalized emission intensity with respect to specific amount of two nitrophenol derivatives are plotted (Figure ).…”

“…Hence, less significant host dependent emission quenching shown by a particular nitrophenolic compound with different imidazole tethered imide hosts suggested an intermolecular quenching mechanism. Upon acidification of the imidazole by mineral acid in analogous naphthalimide derivative increased the intensity of emissions due to photo‐electron transfer (PET). This was also true in the present case, as we found that added mineral acid increased the fluorescence emission intensity of L 1 and L 2 .…”

Systematic Study of Solid-State Fluorescence and Molecular Packing of Methoxy-trans-Stilbene Derivatives, Exploration of Weak Intermolecular Interactions Based on Hirshfeld Surface Analysis

“…Among the factors resulting from the molecular arrangement in the crystal lattice, which influences the fluorescent properties, the occurrence of hydrogen bonds and π-π stacking interactions can be detected [ 8 ]. However, the literature is uncertain if the presence of these factors has a positive or negative effect on properties such as fluorescence quantum yield or fluorescence lifetime [ 9 , 10 , 11 , 12 , 13 ]. These occurrences are promoted by numerous complex mechanisms, such as aggregation-induced emission (AIE) or aggregation caused-quenching (ACQ), that can co-occur.…”