Theory of light quenching: effects of fluorescence polarization, intensity, and anisotropy decays

Abstract

Experimental studies have recently demonstrated that fluorescence emission can be quenched by laser light pulses from modern high repetition rate lasers, a phenomenon we call "light quenching." We now describe the theory of light quenching and some of its effects on the steady-state and time-resolved intensity and anisotropy decays of fluorophores. Light quenching can decrease or increase the steady-state or time-zero anisotropy. Remarkably, the light quenching can break the usual z axis symmetry of the excited-state population, and the emission polarization can range from -1 to +1 under selected conditions. The measured anisotropy (or polarization) depends upon whether the observation axis is parallel or perpendicular to the propagation direction of the light quenching beam. The effects of light quenching are different for a single pulse, which results in both excitation and quenching, as compared with a time-delayed quenching pulse. Time-delayed light quenching pulses can result in step-like changes in the time-dependent intensity or anisotropy and are predicted to cause oscillations in the frequency-domain intensity and anisotropy decays. The increasing availability of pulsed laser sources offers the opportunity for a new class of two-pulse or multiple-pulse experiments where the sample is prepared by an excitation pulse, the excited state population is modified by the quenching pulse(s), followed by time- or frequency-domain measurements of the resulting emission.

Photoluminescence properties of polystyrene-hosted fluorophore thin films

“…25 In such cases, the fluorescence emission may have preferential direction as well, which is azimuthally symmetric, but anisotropic with respect to the direction normal to the thin-film surface. 14,36 Although, in our experiments, all measurements are performed at a certain elevation angle with respect to the normal to the thin film surface, time-resolved and steady state anisotropy measurements may lead to more complete understanding of the emission processes.…”

Fluorescence-Lifetime Imaging Techniques for Microscopy

“…The most common implementation is transient absorption (Fleming, 1986). Recently, applications using pump-probe spectroscopy with stimulated emission have also been reported (Lakowicz et al, 1994b;Kusba et al, 1994). With stimulated emission, one can either measure the stimulated emission directly or the resulting change in fluorescence emission intensity.…”

Light quenching effects at high-saturation conditions

“…The induced transitions can be initiated by both the exciting radiation and independent radiation sources. As the light quenching is associated with selective deactivation of the excited states, the effect exhibits a strong dependence on the polarizations of exciting and quenching radiations, thus exerting influence on the luminescence polarization [2][3][4]. Because of this, the light quenching has been extensively used to study different characteristics of complex molecular compounds [3][4][5].…”

“…As the light quenching is associated with selective deactivation of the excited states, the effect exhibits a strong dependence on the polarizations of exciting and quenching radiations, thus exerting influence on the luminescence polarization [2][3][4]. Because of this, the light quenching has been extensively used to study different characteristics of complex molecular compounds [3][4][5]. The induced transitions from the excited states have attracted even greater interest of researchers since the introduction of a new high-resolution microscopy method, a stimulated-radiation depletion (STED) microscopy [6,7].…”

“…There is no possibility to solve such a complex self-consistent problem on the basis of rate equations usually used when studying the light quenching [2][3][4]8]. As will be shown later, this problem hardly allows derivation of analytical solutions even for relatively simple cases.…”