@article{kee_kirmaier_yu_thamyongkit_youngblood_calder_ramos_noll_bocian_scheidt_et al._2005, title={Structural control of the photodynamics of boron-dipyrrin complexes}, volume={109}, ISSN={["1520-5207"]}, DOI={10.1021/jp0525078}, abstractNote={Boron-dipyrrin chromophores containing a 5-aryl group with or without internal steric hindrance toward aryl rotation have been synthesized and then characterized via X-ray diffraction, static and time-resolved optical spectroscopy, and theory. Compounds with a 5-phenyl or 5-(4-tert-butylphenyl) group show low fluorescence yields (approximately 0.06) and short excited-singlet-state lifetimes (approximately 500 ps), and decay primarily (>90%) by nonradiative internal conversion to the ground state. In contrast, sterically hindered analogues having an o-tolyl or mesityl group at the 5-position exhibit high fluorescence yields (approximately 0.9) and long excited-state lifetimes (approximately 6 ns). The X-ray structures indicate that the phenyl or 4-tert-butylphenyl ring lies at an angle of approximately 60 degrees with respect to the dipyrrin framework whereas the angle is approximately 80 degrees for mesityl or o-tolyl groups. The calculated potential energy surface for the phenyl-substituted complex indicates that the excited state has a second, lower energy minimum in which the nonhindered aryl ring rotates closer to the mean plane of the dipyrrin, which itself undergoes some distortion. This relaxed, distorted excited-state conformation has low radiative probability as well as a reduced energy gap from the ground state supporting a favorable vibrational overlap factor for nonradiative deactivation. Such a distorted conformation is energetically inaccessible in a complex bearing the sterically hindered o-tolyl or mesityl group at the 5-position, leading to a high radiative probability involving conformations at or near the initial Franck-Condon form of the excited state. These combined results demonstrate the critical role of aryl-ring rotation in governing the excited-state dynamics of this class of widely used dyes.}, number={43}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={Kee, HL and Kirmaier, C and Yu, LH and Thamyongkit, P and Youngblood, WJ and Calder, ME and Ramos, L and Noll, BC and Bocian, DF and Scheidt, WR and et al.}, year={2005}, month={Nov}, pages={20433–20443} }
 @article{muthukumaran_zaidi_yu_thamyongkit_calder_sharada_lindsey_2005, title={Synthesis of dipyrrin-containing architectures}, volume={9}, ISSN={["1099-1409"]}, DOI={10.1142/S108842460500085X}, abstractNote={ Dipyrrins are valuable precursors to dyes [dipyrrinatoboron difluoride, bis(dipyrrinato)-zinc(II) complexes] and serve as ligands in a variety of self-assembled materials. Six new dipyrrin-containing architectures have been synthesized. The architectures include bis(dipyrrinato) complexes containing copper(II) or palladium(II), a dipyrrin bearing a protected phosphonic acid unit, a porphyrin bearing two dipyrrins in a trans configuration, a linear diphenylethyne-linked dipyrromethane-dipyrrin building block, and a triad composed of two zinc porphyrins joined via an intervening bis(dipyrrinato)copper(II) complex. Two porphodimethenatozinc complexes were prepared and found to have Φ f  ≤ 0.002 (in toluene at room temperature), which is substantially less than the analogous bis(dipyrrinato)zinc complexes. Taken together, the syntheses described herein should broaden access to dipyrrins for use as complexation motifs in supramolecular chemistry and as pigments in light-harvesting applications. }, number={10-11}, journal={JOURNAL OF PORPHYRINS AND PHTHALOCYANINES}, author={Muthukumaran, Kannan and Zaidi, Syeda Huma H. and Yu, Lianhe and Thamyongkit, Patchanita and Calder, Matthew E. and Sharada, Duddu S. and Lindsey, Jonathan S.}, year={2005}, pages={745–759} }