Expanded pyridiniums: bis-cyclization of branched pyridiniums into their fused polycyclic and positively charged derivatives--assessing the impact of pericondensation on structural, electrochemical, electronic, and photophysical features.
This study evaluates the impact of the extension of the π-conjugated system of pyridiniums on their various properties. The molecular scaffold of aryl-substituted expanded pyridiniums (referred to as branched species) can be photochemically bis-cyclized into the corresponding fused polycyclic derivatives (referred to as pericondensed species). The representative 1,2,4,6-tetraphenylpyridinium (1(H)) and 1,2,3,5,6-pentaphenyl-4-(p-tolyl)pyridinium (2(Me)) tetra- and hexa-branched pyridiniums are herein compared with their corresponding pericondensed derivatives, the fully fused 9-phenylbenzo[1,2]quinolizino[3,4,5,6-def]phenanthridinium (1(H)f) and the hitherto unknown hemifused 9-methyl-1,2,3-triphenylbenzo[h]phenanthro[9,10,1-def]isoquinolinium (2(Me)f). Combined solid-state X-ray crystallography and solution NMR experiments showed that stacking interactions are barely efficient when the pericondensed pyridiniums are not appropriately substituted. The electrochemical study revealed that the first reduction process of all the expanded pyridiniums occurs at around -1 V vs. SCE, which indicates that the lowest unoccupied molecular orbital (LUMO) remains essentially localized on the pyridinium core regardless of pericondensation. In contrast, the electronic and photophysical properties are significantly affected on going from branched to pericondensed pyridiniums. Typically, the number of absorption bands increases with extended activity towards the visible region (down to ca. 450 nm in MeCN), whereas emission quantum yields are increased by three orders of magnitude (at ca. 0.25 on average). A relationship is established between the observed differential impact of the pericondensation and the importance of the localized LUMO on the properties considered: predominant for the first reduction process compared with secondary for the optical and photophysical properties.
Fortage
Jérôme
J
Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques (CNRS UMR-8601), Université Paris Descartes, 45, rue des Saints Pères, 75270 Paris Cedex 06, France.
Tuyèras
Fabien
F
Ochsenbein
Philippe
P
Puntoriero
Fausto
F
Nastasi
Francesco
F
Campagna
Sebastiano
S
Griveau
Sophie
S
Bedioui
Fethi
F
Ciofini
Ilaria
I
Lainé
Philippe P
PP
D018360:Crystallography, X-Ray; D003500:Cyclization; D004563:Electrochemistry; D004581:Electronics; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011083:Polycyclic Compounds / Q000737:chemistry*; D011726:Pyridinium Compounds / Q000737:chemistry*
D011083:Polycyclic Compounds; D011726:Pyridinium Compounds