ABSTRACT
We report the spectroscopic characterization of dimethylvinylidene, (CH3)2C=C:, generated within an argon matrix at 14 K from a bisperoxyester precursor. The carbene was identified by comparison of the experimental IR spectrum with vibrational frequencies computed at the B3LYP/6-31G(d) level. Chemical trapping of the carbene within a 9% CO/Ar matrix to form dimethylpropadienone supports this analysis. Additional products produced during photolysis were identified by comparison to the appropriate computed vibrational frequencies. The potential energy surface of dimethylvinylidene and its intramolecular rearrangement products, 2-butyne and methylcyclopropene, were also investigated computationally at the B3LYP/6-31G(d) level. A spin-state analysis of this carbene using a variety of computational methods (CCSD(T), B3LYP, MP2) indicates the singlet state is more stable than the triplet by approximately 45 kcal mol-1. We anticipate the bisperoxyester precursor used here will be a convenient and general way for initiating future studies of alkylvinylidenes under matrix-isolation conditions.
ABSTRACT
The synthesis and photophysical characterization of a series of free base porphyrin-containing polyamide dendrimers terminated with anthraquinone groups (FbP-Ga-AQ(n)(), a = 1-3, n = 12, 36, 108) are described. Substantial quenching (58-75%) of the porphyrin fluorescence of FbP-Ga-AQ(n)() is observed when compared to the analogous ethyl-terminated dendrimers (FbP-Ga-Et(n)()) in steady-state fluorescence experiments and is attributed to intramolecular electron transfer. Time-resolved fluorescence experiments were fit to 2-3 exponentials, indicating multiple orientations for electron transfer, consistent with the flexible nature of these dendrimers.
