Electronic transitions in a series of 2-azaazulene polymethine dyes with different pi-conjugation lengths
Abbreviated Journal Title
Polymethine; 2-Azaazulenes; pi-Conjugated chain; Terminal groups; Symmetry breaking; Wave of charge; Bond length alternation; Quantum; chemical calculations; Localized and delocalized molecular orbitals; NEGATIVE-DEFECT TRANSPOLYACETYLENE; SYMMETRY-BREAKING; ABSORPTION; ANISOTROPY; FINITE-LENGTH; CYANINE DYES; SOLITONS; CHROMOPHORES; SPECTRA; CATIONS; Chemistry, Physical; Physics, Atomic, Molecular & Chemical
A comprehensive quantum chemical analysis along with spectral-luminescence measurements has been performed for a new series of 2-azaazulene dyes with different conjugation lengths (n) to better understand the nature of their electronic transitions. The remarkably large red shift of their main absorption bands at relatively small n is connected with the existence of totally delocalized HOMO and LUMO. Symmetry breaking is observed experimentally at n = 3 in polar solvents and theoretically at n = 5 in vacuum. Analysis shows the existence of two types of molecular orbitals (MOs): local with the charge mainly localized within the terminal groups, and delocalized with the charge distributed throughout the molecule. Correspondingly, three types of electronic transitions are present: between delocalized MOs; between one local and one delocalized MO, and between local MOs only, which is important for predicting the positions of electronic transitions to the chain length. (C) 2012 Elsevier B.V. All rights reserved.
"Electronic transitions in a series of 2-azaazulene polymethine dyes with different pi-conjugation lengths" (2013). Faculty Bibliography 2010s. 4553.