Experimental and computational study of the maximum absorption wavelength of conjugated systems

• Main Authors: Adonay, Katrina Ejercito, Cabral, Marywinn San Juan
• Format: text
• Language: English
• Published: Animo Repository 2004
• Subjects: Wavelengths; Length measurement
• Online Access: https://animorepository.dlsu.edu.ph/etd_bachelors/10029
• Institution: De La Salle University

The electronic spectra of five conjugated systems (2 polymethine dyes and 3 polyenes) were determined by UV-Vis spectroscopy and calculated using ZINDO with INDO/1 parameters in the CAChe software. These systems were 1,1-diethyl1-2,2'-cyanine iodide, 1,1'-diethyl-2,2'-carbocyanine chloride All-trans retinoic acid Vitamin A Palminatate 1.7 m. IU/g and Beta-carotene 10% CWS. The max of these systems were computed using the energy expression for the particle-in-a-box. The lengths of the box were obtained using several methods: (a) adding up the bonds in the chain using the average C-C and C-N bond lengths of conjugated systems, (b) adding one additional bond length to each end of the chain calculated in (a) (c) adding up individual bond lengths in the chain (d) getting the bond length from the CAChe drawing and (e) adding one additional bond length to each end of the chain calculated in (d) The results showed that the experimental and the literature values of wavelength of maximum absorption gave a good agreement. The results confirmed the predicted trend that as the box length increases, the wavelength of maximum absorption increases. The computed max using the simple energy expression from P-1-B gave poor agreement with experimental values. The polymethine dyes, however, gave better agreement than polyenes (Beta-carotene, Vitamin A and retinoic Acid). When a step potential was used for the polyenes, better agreement was given. Between the experimental max and the computed max the best agreement was made with the max that is obtained from CAChe. When penetration was added to the box lengths, a significant improvement was observed in all systems.