**1. Introduction**

86 Macro to Nano Spectroscopy

*Emm* 

31 19 (6.626) 10 9.91452 2.18 10

We have demonstrated a more convenient synthesis method for colloidal CdSe quantum dots. This method does not involve quenching. This makes it easier for students to make the semiconductor nanoparticles. This synthesis method depends on different heating times for

Congresswoman Corrine Brown who was instrumental in procuring EWC grant to

Army Research Laboratory and Dr N. Sundaralingam, Chair Department of Math and

Dr. Elias Towe, ECE, MSE and Director-CNXT, Carnegie Mellon University for

Finally EWC who made the time available and provided the necessary resources to

[2] Ellis, A. B.; Geselbracht, M. J.; Johnson, B.J.; Lisensky, G.C.; Robinson, W.R.; *American* 

.

*x x <sup>R</sup> x m x xx x x*

9

2 <sup>2</sup> 1 1 8 *ex e h*

*<sup>h</sup> <sup>R</sup>*

2 68

9.1095 10 8 0.78 1.602 10

This leads to diameter of about 4 nm

premixed CdO and Se solutions.

purchase the optical laboratory equipment.

Sciences, Edward Waters College for their assistance.

[1] Tadd, K.; Laura, A. S.; Sandra, J. R. *J. of Chem. Edu*. 2002, 79, 9.

*Chemical Society*, Washington, D.C., 1993.

[7] Peng, Z.A.; Peng, X,; *J. Am. Chem. Soc*., 2001, 123, 183-184.

[8] Yu, W.W.; Peng, X.; *Angew. Chem. Int. Ed. Engl*., 2002, 41, 2368-2371. [9] Peng, Z.A.; Peng, X.J.; *J. Am. Chem. Soc*., 2002, 124, 3343-3353. [10] Elizabeth M. B.; George C. L.; *J. of Chem. Edu*., 2005, 82, 1697-1699.

[3] Schulz, W.G.; *Chem. Eng. News*, 2000, 78, 41. [4] Rawls, R.L.; *Chem. Eng. News*, 2003, 81, 39. [5] Halford, B*.; Chem. Eng. News,* 2004, 82, 5. [6] Wilson, E.K.; *Chem. Eng. News*, 2003, 81, 29.

[11] Brus, L.E.; *J. Chem. Phys*., 1983, 79, 5566-5571. [12] Brus, L.E.; *J. Chem. Phys*., 1984, 80, 4403-4409.

**6. Acknowledgements**  We would like to thank;

collaborative advice.

**7. References** 

conduct this research possible.

**5. Conclusion** 

The porphyrins (Fig. 1) are an important class of naturally occurring macrocyclic compounds found in biological compounds that play a very important role in the metabolism of living organisms. They have a universal biological distribution and were involved in the oldest metabolic phenomena on earth. Some of the best examples are the iron-containing porphyrins found as heme (of haemoglobin) and the magnesium-containing reduced porphyrin (or chlorine) found in chlorophyll. Without porphyrins and their relative compounds, life as we know it would be impossible and therefore the knowledge of these systems and their excited states is essential in understanding a wide variety of biological processes, including oxygen binding, electron transfer, catalysis, and the initial photochemical step in photosynthesis.

The word porphyrin is derived from the Greek porphura meaning purple. They are in fact a large class of deeply coloured pigment, of natural or synthetic origin, having in common a substituted aromatic macrocycle ring and consists of four pyrrole rings linked by four methine bridges (Milgrom, 1997; D. Dolphin, 1978).

Fig. 1. The structure of porphyrin.

The porphyrins have attracted considerable attention because are ubiquitous in natural systems and have prospective applications in mimicking enzymes, catalytic reactions, photodynamic therapy, molecular electronic devices and conversion of solar energy. In particular, numerous porphyrins based artificial light-harvesting antennae, and donor acceptor dyads and triads have been prepared and tested to improve our understanding of the photochemical aspect of natural photosynthesis.

The Use of Spectrophotometry UV-Vis for the Study of Porphyrins 89

discovered that the addition of metal salts to the reaction mixture, such as zinc acetate, increases the yield of porphyrin from 4-5% for the free-base derivative, and decreases the amount of chlorin compound. Others improvement were obtained by changing opportunely

Adler, Longo and coworkers, in the 1960s (Adler et al. 1967), re-examined the synthesis of *meso*substituted porphyrins and developed an alternative approach (Fig. 3) with a method that involves an acid catalyzed pyrrole aldehyde condensation in glassware open to the atmosphere in the presence of air. The reactions were carried out at high temperature, in different solvents and concentrations range of reactants with a yields of 30-40%, and with

Over the period 1979-1986, Lindsey developed a new and innovative two-step room temperature method to synthesize porphyrins, motivated by the need for more gentle conditions for the condensation of aldehydes and pyrrole, in order to enlarge the number of the aldehydes utilizable and then the porphyrins available (Anderson et al., 1990; Acheson et al., 1976; Dailey, 1990; Porra, 1997; Mauzarall, 1960). The method has been a new strategy for the synthesis of porphyrins, using a sequential process of condensation and oxidation steps. The reactions were carried out under mild conditions in an attempt to achieve equilibrium during condensation, and to avoid side reactions in all steps of the porphyrin-

The porphyrin macrocycle is a highly-conjugated molecule containing 22 -electrons, but only 18 of them are delocalized according to the Hückel's rule of aromaticity (4n+2

chlorin contamination lower than that obtained with the Rothemund synthesis.

Fig. 3. Adler-Longo method for preparing *meso*-substituted porphyrins.

forming process (Fig. 4)

delocalized -electrons, where n = 4).

the reaction conditions and substituents in benzaldehyde molecule framework.

Fig. 2. Synthesis of 5,10,15,20-tetraphenyl porphyrin.

The porphyrins play important roles in the nature, due to their special absorption, emission, charge transfer and complexing properties as a result of their characteristic ring structure of conjugated double bonds (Rest et al.,1982).

As to their electronic absorption, they display extreme intense bands, the so-called Soret or B-bands in the 380–500 nm range with molar extinction coefficients of 105 M-1 cm-1. Moreover, at longer wavelengths, in the 500–750-nm range, their spectra contain a set of weaker, but still considerably intense Q bands with molar extinction coefficients of 104 M-1 cm-1. Thus, their absorption bands significantly overlap with the emission spectrum of the solar radiation reaching the biosphere, resulting in efficient tools for conversion of radiation to chemical energy. In such a conversion, the favourable emission and energy transfer properties of porphyrin derivatives are indispensable as in the case of chlorophylls, which contain magnesium ion in the core of the macrocycle. Also, metalloporphyrins can be utilized in artificial photosynthetic systems, modelling the most important function of the green plants (Harriman et al., 1996).

The studies of the wavelength shift of their adsorption band and the absorbance changes as function of pH, temperature, solvent change, reaction with metal ions and other parameters permits to obtained accurate information about equilibrium, complexation, kinetic and aggregation of porphyrins.

This review, resumes the best successes in the use of spectrophotometer UV-Vis for explained the chemical characteristics of this extraordinary group of natural occurring molecules and clarifies the potential of these molecules in many fields of application.
