Solvatochromism of a highly conjugated novel donor-π-acceptor dipolar fluorescent probe and its application in surface-energy transfer with gold nanoparticles

A novel highly conjugated donor-π-acceptor (D-π-A) fluorescent probe 4-((1E,3E)-4-(4-(5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl)phenyl)buta-1,3-dienyl)-N,N-dimethylbenzenamine (3TVPO) is synthesized using a Wittig reaction and characterized by 1H, 13C NMR, FT-IR spectroscopy and high-resolution mass spectrometry (HR-MS). The photophysical properties have been studied to understand the intramolecular charge-transfer (ICT) character of the compound. The solvatochromism of 3TVPO has been explored in polar protic/aprotic/weakly polar solvents. Various solvent correlation techniques such as Lippert-Mataga, Bilot-Kawski, Kawski-Chamma-Viallet, Bakhshiev, and Reichardt methods were employed to estimate the singlet ground- and excited-state dipole moment and are compared and discussed with those obtained computationally. The specific and non-specific solute-solvent interactions were analyzed using Kamlet-Taft and Catalán solvent parameters by means of a multiple-linear-regressions (MLR) method. In addition, surface-energy transfer (SET) has been studied using this optoelectronically important 3TVPO molecule as efficient donor and gold nanoparticles (Au MNPs) as excellent acceptors employing steady-state and time-resolved spectroscopic techniques. The size- and distance-dependent SET between 3TVPO and Au MNPs was explored. It is demonstrated that the quenching efficiency increases as the size of Au MNPs increases from 40 to 53 nm. The super-quenching effect and nonradiative energy transfer were analyzed using Stern-Volmer plots. The impact of the present investigation about the super-quenching effect of the Au MNPs can be exploited for biosensing applications owing to its acute sensitivity.