Dipole Moments of 4?-Aminoflavonol Fluorescent Probes in Different Solvents

Abstract

Electrooptical absorption measurements (EOAM) were used to measure the dipole moments of the normal form of 4'-(dimethylamino)-3-hydroxyflavone (FME), and 4' N-(15-azacrown-5)-3-hydroxyflavone (FCR) in 1,4-dioxane, toluene, and cyclohexane. With these probes excited-state intramolecular proton transfer (ESIPT) takes place. For comparison, the dipole moments of 4'-(dimethylamino)-3-metoxyflavone (FME3ME), for which ESIPT is lacking, were measured, too. For all three probes the ground (micro(g)) and excited Franck-Condon state (micro(e)FC) electrical dipole moments are parallel to each other and also parallel to the transition dipole moment. The electrical dipole moments of FCR, FME, and FME3ME in their ground state have values within the range (12.0-17.7) x 10(-30) C m. Upon optical excitation, the dipole moments increase by (41.9-52.9) x 10(-30) C m. The value of the change of the dipole moment vector delta(a)micro with excitation to the Franck-Condon state and the value of the vector micro(e)FC for FCR and FME are practically independent on the solvent polarity. From this point of view and due to large values of the dipole moments FCR and FME are very promising probes for the investigation of the distribution of the local polarity in biological systems using site-selective excitation of the different sites. Our steady-state fluorescence studies on FME and FCR have demonstrated a high spectral sensitivity of the normal form to such solvent characteristics as polarity.

Ultrafast Ground-State Intramolecular Proton Transfer in Diethylaminohydroxyflavone Resolved with Pump–Dump–Probe Spectroscopy

“…Therefore, N* and T* are subjected to different solvent polarization configurations, which results in a solvation-induced barrier to the ESIPT reaction, N* → T*. ,, The T* fluorescence band is characterized as locally excited emission because of the relatively small difference in dipole moments between T* and T, in line with the much smaller frequency shift of the T* emission with solvent polarity. These dipole moments agree well with TDDFT-RISM calculations performed by Sato and coworkers but are a little larger in magnitude than the previous CIS calculations by Chou and coworkers. , Nemkovich et al also characterized the significant changes in dipole moment upon optical excitation by electro-optical absorption measurements . Finally, we note that both absorption of N and emission of T* result in a shortened and presumably strengthened intramolecular hydrogen bond.…”

“…10,12 Nemkovich et al also characterized the significant changes in dipole moment upon optical excitation by electro-optical absorption measurements. 40 Finally, we note that both absorption of N and emission of T* result in a shortened and presumably strengthened intramolecular hydrogen bond.…”

Effect of positional substitution of amino group on excited state dipole moments of quinoline

“…However, the experimental determination of dipole moment based on the analysis of the solvatochromism of absorption and fluorescence maxima is quite popular. Many workers have reported the ground state and excited state dipole moments using different solvatochromic methods [17][18][19][20][21][22][23][24][25][26][27].…”

Understanding Structural Changes through Excited-State Intramolecular Proton Transfer in 4′-N,N-Diethylamino-3-hydroxyflavone (DEAHF) in Solution Based on Quantum Chemical Calculations

“…In the ground state, DEAHF exists only in the normal form (N). In the excited state, an excited-state intramolecular proton transfer (ESIPT) reaction occurs, and both the normal (N*) and tautomer (T*) forms exist in solution. ,,,− The radiative decay process of this molecule has already been discussed in detail both experimentally and theoretically. The fluorescence on the blue side was assigned to the N* form excited state (around 530 nm), and the fluorescence on the red side was assigned to the T* form excited state (around 570–600 nm).…”

“…The fluorescence on the blue side was assigned to the N* form excited state (around 530 nm), and the fluorescence on the red side was assigned to the T* form excited state (around 570–600 nm). The ESIPT dynamics of DEAHF have been studied using time-resolved fluorescence spectroscopy, ,− TA spectroscopy, , and theoretical calculations. ,,,,− Nevertheless, to the best of our knowledge, the electronic structure changes through ESIPT in DEAHF are still not fully understood.…”