ORIGINAL PAPER Fluorescence Quenching N,N-Bis(2,6-Dimethylphenyl) -3,4:9,10-Perylenetetracarboxylic Diimide (BDPD) Laser Dye by Colloidal Silver Nanoparticles Samy A. El-Daly & Ibrahim A. Salem & Mahmoud A. Hussein & Abdullah M. Asiri Received: 13 October 2014 /Accepted: 20 January 2015 # Springer Science+Business Media New York 2015 Abstract The fluorescence quenching N,N-bis(2,6- dimethylphenyl)-3,4:9,10-perylenetetra-carboxylic diimide (BDPD) by colloidal silver nanoparticles (AgNPs) was stud- ied in methanol and ethylene glycol by steady state fluores- cence measurements. The Stern - Volmer quenching rate con- stant (K sv ) was calculated as 8.1×10 8 and 8.22×10 8 M -1 in methanol and ethylene glycol respectively. Taking the fluores- cence lifetime of BDPD in the absence of silver nanoparticles as 3.2 ns, the values of the fluorescence quenching rate con- stants (k q =K sv /τ) are calculated as 2.54×10 17 and 2.56× 10 17 M -1 s -1 in methanol and ethylene glycol respectively. From the data, fluorescence resonance energy transfer and / or electron transfer processes play a major role in the fluores- cence quenching of BDPD by AgNPs in methanol and low concentrations of Ag NPs in ethylene glycol. The static quenching rate constant in ethylene glycol was calculated by modified Stern - Volmer equation as V=8.86×10 9 M -1 . For dynamic quenching, the radius of quenching sphere volume r values were found to be 68.3 and 70.6 nm in ethanol and ethylene glycol, respectively. For static quenching in ethylene glycol the effective radius of quenching sphere action (kinetic radius) was calculated as r =152 nm. Keywords N,N-Bis(2,6-dimethylphenyl)-3,4:9,10-perylene- tetracarboxylic diimide . Fluorescence quenching . Silver nano-particles Introduction The rapid development of nanotechnology over the last sev- eral decades has opened new possibilities for investigating the interaction between photo-excited molecules and metallic nanoparticles. Thus, in recent years there has been a growing interest in the interactions of fluorophores with metallic nano- structures or nanoparticles [1]. The spectral properties of fluorophores can be dramatically modified by near-field inter- actions with the electron clouds present in metals. These in- teractions modify the emission in ways not seen in ensemble fluorescence experiments [2]. The type, size and shape of the metallic nanoparticles can modulate the fluorescence of a tar- get dye close to the metal surface. The enhancement of fluo- rescence efficiency due to electronic coupling of the electronic transition dipole moment with surface Plasmon is a desirable effect owing to the use of medium to low-quantum yield fluorophores in molecular probing devices [3, 4]. The quenching of organic fluorophores by small molecules is thought to arise from dynamic quenching [5–7]. Other reports conclude that both dynamic and static mechanisms are in- volved in the quenching process [8–10]. Interactions between fluorophores and noble nanoparticles have been investigated S. A. El-Daly (*) : M. A. Hussein : A. M. Asiri Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia e-mail: samyeldaly@yahoo.com M. A. Hussein : A. M. Asiri Center of Excellence for Advanced Materials Research (CEAMR), King Abdulaziz University, Jeddah 21589, P.O. Box 80203, Saudi Arabia S. A. El-Daly : I. A. Salem Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt M. A. Hussein Chemistry Department, Faculty of Science, Assiut University, Assiut 71516, Egypt J Fluoresc DOI 10.1007/s10895-015-1523-3