New porphyrins tailored as biodiesel fluorescent markers Ana Cecília B. Figueira a , Kleber T. de Oliveira b , Osvaldo A. Serra a, * a Laboratório de Terras Raras, Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo e USP, Av. Bandeirantes, 3900, CEP 14040-901, Ribeirão Preto, SP, Brazil b Departamento de Química, Universidade Federal de São Carlos e UFSCar, São Carlos, SP, Brazil article info Article history: Received 11 April 2011 Received in revised form 16 May 2011 Accepted 19 May 2011 Available online 27 May 2011 Keywords: Porphyrins Biodiesel marker Tagging Fluorescent markers Fuel markers Biodiesel label abstract This work reports the synthesis, characterization, and evaluation of new porphyrins tailored to become biodiesel fluorescent markers. The compounds were obtained by the synthetic modification of the commercially available porphyrin 5,10,15,20-meso-tetrakis(pentafluorophenyl)porphyrin (TPPF 20 ) using ethanol and hexadecan-1-ol (cetylic alcohol) as nucleophilic reagents. The stability of the marked biodiesel fuel solutions was investigated every 15 days for a total period of 3 months, and under different storage temperature and light exposure condition, simulating the conventional stock conditions. The influence of the different substituents of the porphyrins on the fluorescence properties of the biodiesel fuel markers was also assessed. The resulting porphyrins were highly soluble in biodiesel fuel and displayed strong fluorescence characterized by two strong emission bands. The fluorescent markers did not affect the biodiesel physical properties and were stable in storage conditions for at least 3 months at a concentration of 4 ppm. The best storage condition was found to be absence of light and 6  C; the limit of detection by pho- toluminescence technique had magnitude of 10 13 mol L 1 . The synthesized porphyrins were characterized by nuclear magnetic resonance ( 1 H-NMR and 19 F- NMR), mass spectrometry (HRMS), ultraviolet visible absorption spectroscopy, and photoluminescence spectroscopy. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction It is well known that the fuel industry is one of the most important and profitable commercial areas. Fuel production, distribution, and taxation policies are the exclusive responsibility of each country or government. The fuel rating process itself relies on the characteristics of each fuel, especially those regarding its uses and applicability. In this context, the fact that the same fuel can be used for different purposes is taken into account, thereby leading to distinct taxations [1]. Unfortunately over the years the fraudulent adulteration of fuels has been rising, which means that their indiscriminate misuse is growing fast due to a mixture of low quality products with premium- quality ones. Even solvents that serve a different kind of application are being added to fuels, to guarantee low prices on a daily basis. Hence, it is mandatory that new policies are developed in order to fight against this kind of practice. Fuel tagging or marking, appears to be one of the most important measures in this sense, because it allows for fuel quantification and identification, their origin along with production chain. Therefore, this method is a potential procedure for discouraging this kind of misuse or making it at least traceable. Friswell described once that a marker is a substance that can be dissolved in a liquid and later be detected in such liquid by performance of a chemical or physical test on the tagged (marked) liquid. They are necessary for a clear distinction between chemi- cally or physically similar liquids [2]. The fuel marking systems employed in past decades frequently used organic pigments [3]. Several substances have been used to tag petroleum fuel and derivatives, but they all possess negative characteristics such as poor solubility in hydrophobic environment or low stability under storage conditions. Historically, various other problems have accompanied the use of dyes as fuel markers, including crystallization [4] upon standing or storage. A few years ago some coumarin derivatives [2], naph- thalocyanines [4], and phthalocyanines were tested as fluorescent markers for petroleum fuel derivatives because of their fluorescent properties and stability. Besides, these compounds are invisible under the naked eye and visible light, but they can be easily detected by UV light since they offer higher sensitivity compared to the commonly used organic dyes. * Corresponding author. Tel.: þ55 16 3602 4376; fax: þ55 16 3602 4838. E-mail address: osaserra@usp.br (O.A. Serra). Contents lists available at ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig 0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2011.05.020 Dyes and Pigments 91 (2011) 383e388