Effects of Alkyl Substituents on the Excited States of Naphthalene:  Semiempirical Study

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 104; no. 5; pp. 1020 - 1029
• Main Authors: Mora-Diez, Nelaine, Boyd, Russell J, Heard, George L
• Format: Journal Article
• Language: English
• Published: American Chemical Society 10.02.2000
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp993228l

The effects of the successive addition of alkyl substituents (methyl and reduced rings) on the excited states of naphthalene are reported. The calculated electronic states of all the reduced derivatives with two, three, and four substituents are compared with the excited states of their methylated analogues. The excited states of several reduced derivatives with seven and eight substituents are also studied. The AM1 method was used to optimize the geometry of 57 naphthalene derivatives, and excited states were calculated with the ZINDO/S (INDO/S) method. ZINDO/S calculations on naphthalene gave excited states in better agreement with experimental results than with results of other semiempirical (CNDO/S and CNDOL) and ab initio (CIS, TD-HF, and TD-DFT) methods. Successive alkyl substitutions are accompanied by bathochromic displacements of the UV−visible bands, since the occupied orbitals are raised in energy more than the unoccupied orbitals. However, not all available substituent positions in naphthalene alter its orbital energy distribution in the same way when they are occupied by alkyl substituents. Distortion from planarity of the naphthalene skeleton of some reduced derivatives is the cause of “anomalous” bathochromic displacements of the absorption bands.