A new class of cyanine-like dyes with large bond-length alternation.
Cyanines, which represent a class of charged chromophores with an odd number of pi-conjugated carbons, display unique electronic and optical properties attributed to the strong electronic delocalization and the absence of any significant carbon-carbon bond-length alternation (BLA) along their backbones. The flatness of the corresponding electronic potential makes cyanine dyes the compounds to which simple free-electron theory can be applied in the most relevant way. Recently, cations of porphyrin dimers linked by a pi-conjugated bridge with an odd number of carbons and presenting alternating single and triple bonds were shown to possess linear and nonlinear optical properties analogous to those of cyanines. Here, by using a joint theoretical and experimental approach, we demonstrate the correspondence between cyanines and the new class of alkyne carbocations, in spite of their marked difference in BLA.
School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA.
Shino
S
Ohira
Joel M
JM
Hales
Karl J
KJ
Thorley
Harry L
HL
Anderson
Joseph W
JW
Perry
Jean-Luc
JL
Brédas