Intramolecular and intermolecular hydrogen-bonding effects on photophysical properties of 2′-aminoacetophenone and its derivatives in solution

Abstract

Effects of intra- and intermolecular hydrogen-bonds on the photophysical properties of 2'-aminoacetophenone derivatives (X-C6H4-COCH3) having a substituted amino group (X) with different hydrogen-bonding ability to the carbonyl oxygen (X: NH2(AAP), NHCH3(MAAP), N(CH3)2(DMAAP), NHCOCH3(AAAP), NHCOCF3(TFAAP)) are investigated by means of steady-state and time-resolved fluorescence spectroscopy and time-resolved thermal lensing. Based on the photophysical parameters obtained in aprotic solvents with different polarity and protic solvents with different hydrogen-bonding ability, the characteristic photophysical behavior of the 2'-aminoacetophenone derivatives is discussed in terms of hydrogen-bonding and n,pi*-pi,pi* vibronic coupling. The dominant deactivation process of AAP and MAAP in nonpolar aprotic solvents is the extremely fast internal conversion (k(ic)= 1.0 x 10(11) s(-1) for AAP and 3.9 x 10(10) s(-1) for MAAP in n-hexane). The internal conversion rates of both compounds decrease markedly with increasing solvent polarity, suggesting that vibronic interactions between close-lying S1(pi,pi*) and S2(n,pi*) states lead to the large increase in the non-radiative decay rate of the lowest excited singlet state. It is also suggested that for MAAP, which has a stronger hydrogen-bond as compared to AAP, an intramolecular hydrogen-bonding induced deactivation is involved in the dissipation of the S1 state. For DMAAP, which cannot possess an intramolecular hydrogen-bond, the primary relaxation mechanism of the S1 state in nonpolar aprotic solvents is the intersystem crossing to the triplet state, whereas in protic solvents very efficient internal conversion due to intermolecular hydrogen-bonding is induced. In contrast, the fluorescence spectra of AAAP and TFAAP, which have an amino group with a much stronger hydrogen-bonding ability, give strongly Stokes-shifted fluorescence, indicating that these compounds undergo excited-state intramolecular proton transfer reaction upon electronic excitation.

Solvatochromism and fluorescence response of a halogen bonding anion receptor

“…Inter and intramolecular HBing have been shown to facilitate fluorescence quenching. 15 The efficient fluorescence “turn-off” in 2a correlates with previous NMR studies that illustrate stronger binding between 2a and iodide compared to other anions. 5 In the current system, the formation of strong XBs (C-I•••I−) in the 2a•I− complex could allow the necessary spin-orbital coupling for fluorescence quenching to occur.…”

The N‐Arylamino Conjugation Effect in the Photochemistry of Fluorescent Protein Chromophores and Aminostilbenes

“…[16] Ultrafast HB-induced IC has been reported for many other systems. [32,33] Although there are several potential HB acceptors in ABDIs 2, the HB mode associated with the N-arylamino nitrogen is less likely responsible for the excitedstate quenching, as this mode is also present in ACSs 1. As such, either the imino N or the carbonyl O in the imidazolinone group, as depicted for 2 P in methanol (Figure 7), should be responsible.…”

A photochemical approach for evaluating the reactivity of substituted lappaconitines

“…10,[13][14][15][16] According to the modern point of view, intersystem crossing between singlet and triplet excited states in compounds, involving closely located amine and carbonyl groups, might be caused by the vibrational interaction between close-lying S 1 (π,π*) and S 2 (n,π*) states. 28 This interaction leads to a large increase in the non-radiative decay rate of the lowest excited singlet state. At the same time, intermolecular hydrogen bonds, changing the planarity of the nitrogen atom, conversely result in level stabilization and intersystem crossing to a T 1 (n,π*) triplet state.…”