Presence Of Tert-butyl Substituents Research Articles

Photophysical and Photochemical Properties and Aggregation Behavior of Phthalocyanine and Naphthalocyanine Derivatives

The photophysical and photochemical properties of phthalocyanine and naphthalocyanine with similar structures were studied in solution and with density-functional theory (DFT) computational method. The extended π-conjugated system in naphthalocyanines causes a bathochromic shift in UV-Vis, emission and excitation bands, and promotes lesser generation of singlet oxygen in solution when compared to phthalocyanines. Time dependent DFT (TD-DFT) calculations point out the molecular orbitals involved in Q-band transition, corresponding to highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) transition with a concentration of charge along x-axis, while the transition to LUMO+1 is in y-axis direction. The presence of tert-butyl substituents does not affect the molecular orbitals shape, but affect their energies. Aggregation studies in dimethyl sulfoxide (DMSO):water solutions showed that naphthalocyanines studied have more aggregation tendency than the phthalocyanines. DFT studies indicated that stacked-dimers are preferred to rotated-stacked conformation due the interaction between ZnII and nitrogen atom from different monomers.

The Rate of Host-guest Complex Formation of Some Calixarene Derivatives Towards Neutral Aromatic Guests

In order to determine the factors controlling the response time of the selective chemical sensors, the dissociation dynamics of the complexes of cailx[4]arene with p-chloro-trifluoromethyl-benzene was studied with molecular dynamics calculations. The calculated reaction rates show a contradictory temperature dependence in the absence or presence of tert-butyl substituent at the upper rim of calixarene host molecules. While the dissociation rate increases with the temperature in the case of calix[4]arene host, it decreases at higher temperature when tBu-calix[4]arene host is applied. The weak interaction energies and the low activation energy of the dissociation process validate that the complex equilibrium is rather thermodynamically controlled. Overall, the formation-decomposition processes of calix[4]arene host with p-chloro-trifluoromethyl-benzene guest seems to be a few tens faster then the case when tBu-calix[4]arene host is applied. This observation supports applications of the calix[4]arene rather than tBucalix[4]arene as host molecules in chemical sensors with short response time. This finding can contribute to the development of high-speed sensitive chemical sensors.

Organoiron Selenium Complexes. Synthesis and Characterization oftert-Butyl Substituted Cyclopentadienyldicarbonylselenocarboxylate Iron Complexes, Cp′Fe(CO)2SeCOR (Cp′ = C5H5,t-BuC5H4, 1,3-t-Bu2C5H3)

Abstract The organoiron selenides [(C5H5)Fe(CO)2]2(μ-Se) (I), [(t-BuC5H4)Fe(CO)2]2(μ-Se2) (II), and [(1,3-t-Bu2C5H3)Fe(CO)2]2(μ-Se2) (III) were prepared from the reaction of the organoiron dimers [(C5H5)Fe(CO)2]2, [(t-BuC5H4)Fe(CO)2]2 and [(1,3-t-Bu2C5H3)Fe(CO)2]2 with elemental selenium. The above selenides (I), (II) and (III) react with acid chlorides, RCOCl to give the Se-bonded monoselenocarboxylate derivatives [Cp′Fe(CO)2SeCOR] (Cp′ = C5H5, t-BuC5H4, 1,3-t-Bu2C5H3; R = 4-;O2NC6H4, 3,5-(O2N)2C6H3). The presence of tert-butyl substituents on the cyclopentadienyl ring introduces significant changes in the properties of these systems relative to the unsubstituted cyclopentadienyl analogues.