Theoretical and experimental study on intramolecular charge-transfer in symmetric bi-1,3,4-oxadiazole derivatives

Controllable molecular aggregation and fluorescence properties of 1,3,4-oxadiazole derivatives

“…With a further increase in concentration, the two bands split more obviously due to their opposite-directional shift, and the intensity of the peak at 300 nm (H-aggregates) decreases compared to the one at 355 nm; the peak at 355 nm (J-aggregates) red-shifts gradually to 370 nm and is the only one prominent at higher concentrations ( Figure S2b), implying that J-aggregates are the main component in concentrated solutions (~10 -3 M). It should be noted that the intensity of the band at 250 nm, which should be assigned to those transitions to the higher excited states, 37 also increased when the concentration are increasing from 1×10 -6 to 1×10 -4 M, but decease on further concentration increase ( Figure 1c and S2b), indicating that the intensity change should be related with the formation of H-aggregates. However, the detailed mechanism is still beyond our understanding.…”

“…37 The position of main absorption band are almost independent of the concentration ( Figure 1a); only relative absorption intensity of short wavelength (under 300 nm, Figure S1a) and the peak width increase (more obvious from 2×10 -4 M, Figure S1b) with the increasing concentration, indicative of the formation of molecular aggregates. These molecular aggregates can be further confirmed by the photoluminescence excitation and emission spectra (more sensitive to molecular aggregates, Figure 1b-c).It can be seen that the excitation spectrum at the lower concentration (~10 -6 M) in THF presents a main peak at 320 nm( Figure 1c and S2), and is consistence with shape of the absorption spectrum ( Figure 1a).…”

Enhancement of intramolecular charge transfer strength in diphenylamine substituted symmetric 1,3,4-oxadiazole derivatives

“…The two molecules would not exhibit molecule dipole moments, these calculated dipole moment variations should be assigned to the changes in local dipole moments. 34 These relatively large changes in the local dipole moment are a direct evidence of the strong intramolecular charge transfer characteristic of the excited state in DPAOXD and DPAOXDBEN.…”

“…In our previous studies, it has already been proved that alkoxy phenyl substituted 1,3,4-oxadiazole derivatives show obvious intramolecular charge transfer characteristic, in which symmetric molecular structure was demonstrated to be an effective way to enhance their intramolecular charge transfer characteristic. 34 Furthermore, it was also found that the substituted positions and quantities of methoxy groups in symmetric bi-1,3,4-oxadiazole derivatives would affect the intramolecular charge transfer characteristic; and the strength of intramolecular charge transfer could be enhanced by the introduction of methoxy group in the meta-position on the benzene ring or increase of the quantities of substituted methoxy groups. 35 Herein, in order to further increase the strength of intramolecular charge transfer, two diphenylamine substituted symmetric 1,3,4-oxadiazole derivatives named DPAOXD and DPAOXDBEN were synthesized.…”

“…As shown in Scheme 1a, both of the two compounds maintain symmetric molecular structures for that could enhance intramolecular charge transfer characteristic through doubling the transferred charge. 34 In addition, two key points are also considered in this molecular design: (1) to increase the electron-donating ability of the donors: as compared with BOXD-p-OCH 3 in which a methoxy group was introduced in para position on the benzene ring of symmetric bi-1,3-4-oxadiazole derivative (Scheme 1b), the terminal methoxy group was replaced by a stronger donor group, diphenylamine in DPAOXD, which was expected to be able to donate more electrons to the acceptors; (2) to enlarge the charge transfer distance: in DPAOXDBEN, an additional benzene ring was introduced between the two 1,3,4-oxadiazole rings on the basis of the molecular structure of DPAOXD. Experimental studies and theoretical calculations are carried out jointly to illustrate the effect of molecular structural factors on intramolecular charge transfer characteristic.…”