Luminescence and Electrochemical Activity of New Unsymmetrical 3-Imino-1,8-naphthalimide Derivatives

Abstract

A new series of 1,8-naphtalimides containing an imine bond at the 3-position of the naphthalene ring was synthesized using 1H, 13C NMR, FTIR, and elementary analysis. The impact of the substituent in the imine linkage on the selected properties and bioimaging of the synthesized compounds was studied. They showed a melting temperature in the range of 120–164 °C and underwent thermal decomposition above 280 °C. Based on cyclic and differential pulse voltammetry, the electrochemical behavior of 1,8-naphtalimide derivatives was evaluated. The electrochemical reduction and oxidation processes were observed. The compounds were characterized by a low energy band gap (below 2.60 eV). Their photoluminescence activities were investigated in solution considering the solvent effect, in the aggregated and thin film, and a mixture of poly(N-vinylcarbazole) (PVK) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) (50:50 wt.%). They demonstrated low emissions due to photoinduced electron transport (PET) occurring in the solution and aggregation, which caused photoluminescence quenching. Some of them exhibited light emission as thin films. They emitted light in the range of 495 to 535 nm, with photoluminescence quantum yield at 4%. Despite the significant overlapping of its absorption range with emission of the PVK:PBD, incomplete Förster energy transfer from the matrix to the luminophore was found. Moreover, its luminescence ability induced by external voltage was tested in the diode with guest–host configuration. The possibility of compound hydrolysis due to the presence of the imine bond was also discussed, which could be of importance in biological studies that evaluate 3-imino-1,8-naphatalimides as imaging tools and fluorescent materials for diagnostic applications and molecular bioimaging.

Six New Unsymmetrical Imino-1,8-naphthalimide Derivatives Substituted at 3-C Position—Photophysical Investigations

“…These molecules can form a stable amorphous phase, without crystallization and melting during heating above T g ( Figure 2 c). The T m and T g temperatures were observed in line with the trend for substituents: naphthalene < phenanthrene < anthracene < pyrene (a compound with naphthalene substituent described in our former work [ 38 ]). The presence of ethynyl bond (AzNI-6) increased the T 5% , T m and T g compared with the molecule bearing 4-phenyl-benzyle unit (AzNI-5).…”

“…The absorption band with the maximum (λ max ) between 318 nm–349 nm corresponds to π–π* transitions in the imide unit [ 38 ], while the second band from 374 nm to 415 nm seen in UV-Vis spectra of AzNI-3 and AzNI-1 comes from fused phenyl rings, such as pyrene (AzNI-3) and anthracene (AzNI-1) ( Figure 6 and Supplementary Figure S6 ). The absorption band in the lower energies (3.32–2.99 eV) can be attributed to the charge transfer (CT) between the substitutes and naphthalimide (intra molecular charge transfer/locally excited (ICT/LE) nature) [ 22 , 36 , 38 ]. A better degree of conjugation for azomethino-1,8-naphthalimide with anthracene substituent was noticeable, confirmed by NMR and FTIR spectra and the position of λ max in the lower energies [ 38 ].…”

“…The absorption band in the lower energies (3.32–2.99 eV) can be attributed to the charge transfer (CT) between the substitutes and naphthalimide (intra molecular charge transfer/locally excited (ICT/LE) nature) [ 22 , 36 , 38 ]. A better degree of conjugation for azomethino-1,8-naphthalimide with anthracene substituent was noticeable, confirmed by NMR and FTIR spectra and the position of λ max in the lower energies [ 38 ]. Similar behavior was observed for bis-(imino-1,8-naphthalimides) with triphenylamine described in our recent publication [ 36 ].…”

“…In previous works [ 37 , 38 , 44 ], it was found that an increase in photoluminescence through the protonation of the imine bond related to the inhibition of the PET process can take place. The non-radiative decay rates outperformed radiation processes ( Table 4 ).…”

3-(N,N-Diphenylamino)carbazole Donor Containing Bipolar Derivatives with Very High Glass Transition Temperatures as Potential TADF Emitters for OLEDs

“…Low molar mass organic derivatives that can form stable amorphous films are known as molecular glasses or amorphous molecular materials. The derivatives demonstrate transparency, good film forming, and homogeneous properties, and are widely investigated in terms of scientific research and technological development [23][24][25][26][27][28]. Aromatic amines as molecular glasses are in the group of charge-transporting and light emitting layer derivatives and are well known in OLEDs field applications [29][30][31][32].…”