RESUMO
In this work, a donor-acceptor substituted aromatic system ((E)-N-((E)-3-(4 (dimethylamino)phenyl) allylidene)-4-(trifluoromethyl) benzenamine (DPATB) has been synthesized and its detailed photophysics of intramolecular charge transfer process have been explored on the basis of steady state absorption, fluorescence and time resolved spectroscopy in combination with density functional theory calculations. Large solvent dependency fluorescence spectral shift and the calculated large excited state dipole moment clearly indicate an efficient charge transfer occurring from the donor group to the acceptor moiety in the excited state. Effect on addition of acid and pH on steady state spectral properties further reveals excited state charge transfer character. Quantum chemical calculations were performed in order to study the conformation and polarity of DPATB at their ground as well as excited electronic states. The HOMO and LUMO molecular orbital pictures are obtained at DFT level using B3LYP functional and 6-311 + g(d,p) basis set which clearly support excited state intramolecular charge transfer process. The molecular electrostatic potential maps for the optimized ground state, donor twisted and acceptor twisted geometry shed insight on the electrostatic potential and charge distribution in a system which gives information about the reacting site of the probe and nature of the reaction. In this work, detailed photophysics of excited state intramolecular charge transfer process in donor-acceptor system (DPATB) was evaluated using steady state and time-resolved fluorescence spectroscopy in combination with density functional theory calculations. Large solvent dependency fluorescence spectral shift and the calculated large excited state dipole moment clearly indicate an efficient charge transfer occurring in DPATB. Molecular orbital pictures as obtained from DFT based computational analysis reveals a significant change in the distribution of electron density upon transition from HOMO to LUMO which confirms an ICT process occurring from the donor group to the acceptor moiety in the excited state.
RESUMO
Fluorescence properties of N, N'-bis(salicylidene) trans 1, 2-diaminocyclohexane (H 2 L) is used to probe the anionic (SDS), cationic (CTAB) and nonionic (TX-100) micelles as well as in serum albumins (BSA and HSA) and chicken egg white lysozyme (LYZ) by steady state and picosecond time-resolved fluorescence spectroscopy. The fluorescence band intensity was found to increase with concomitant blue-shift with gradual addition of different surfactants. All the experimental results suggest that the probe molecule resides in the micelle-water interface rather than going into the micellar core. However, the penetration is more towards the micellar hydrocarbon core in nonionic surfactant (TX-100) while comparing with ionic surfactants (SDS and CTAB). Several mean microscopic properties such as critical micelle concentration, polarity parameters and binding constant were calculated in presence of different surfactants. The decrease in nonradiative decay rate constants in micellar environments indicates restricted motion of the probe inside the micellar nanocages with increasing fluorescence emission intensity and quantum yields. Further in this work, we also investigated the interaction behavior of the probe with different proteins at low concentrations under physiological conditions (pH = 7.4). Stern-Volmer analysis of the tryptophan (Trp) fluorescence quenching data in presence of probe reveals Stern-Volmer constant (Ksv) as well as bimolecular quenching rate constant (Kq). The binding constant as well as the number of binding sites of the probe with proteins were also monitored and found to be 1:1 stoichiometry ratio.
