Using selective methyl substitution, we study the effects of vibrational dynamics at conical intersections in unsaturated hydrocarbons. Here, we investigate the excited state nonadiabatic dynamics of cycloheptatriene (CHT) and its relation to dynamics in other polyenes by comparing CHT with 7-methyl CHT, 7-ethyl CHT, and perdeuterated CHT using time-resolved photoelectron spectroscopy and photoelectron anisotropy. Our results suggest that, upon ππ*-excitation to the bright 2A" state, we observe an early intersection with the dark 2A' state close to the Franck-Condon region with evidence of wavepacket bifurcation. This indicates that the wavepacket evolves on both states, likely along a planarization coordinate, with the majority of the flux undergoing nonadiabatic transition via conical intersections within 100 fs following light absorption. In CHT, large amplitude motion along the planarization coordinate improves the intra-ring π-overlap, yielding a delocalized electronic density. However, substitutions in 7 position, chosen to modify the inertia of the planarization motion, did not markedly alter the first step in the sequential kinetic scheme. This suggests that there is a crossing of potential energy surfaces before planarization is achieved and, thus, nonadiabatic transition likely takes place far away from a local minimum.

Pyrene reacts with potassium thiocyanate and organic isothiocyanates in the presence of trifluoromethanesulfonic acid to afford primary and secondary pyrene-1-carbothioamides in high yields.These compounds were efficiently oxidatively desulfurized with Oxone® to the corresponding carboxamides. The amides display solid-state fluorescence with quantum efficiencies up to 62%, originating from monomers, aggregates (such as preformed dimers), and/or excimers, depending on the substituent at the nitrogen atom. Single crystal X-ray diffraction characterization of one highly emissive compound supports this assumption.

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Blue-to-green mechanofluorochromism of pyrene-derived amidophosphonates with methyl, isopropyl and phenyl side groups is reported.