Dissection of stereoelectronic effects in the transition states (TSs) for noncatalyzed azide-alkyne cycloadditions suggests two approaches to selective transition state stabilization in this reaction. First, the formation of both 1,4- and 1,5-isomers is facilitated via hyperconjugative assistance to alkyne bending and C···N bond formation provided by antiperiplanar σ-acceptors at the propargylic carbons. In addition, the 1,5-TS can be stabilized via attractive C-H···F interactions. Although the two effects cannot stabilize the same transition state for the cycloaddition to α,α-difluorocyclooctyne (DIFO), they can act in a complementary, rather than competing, fashion in acyclic alkynes where B3LYP calculations predict up to ∼1 million-fold rate increase relative to 2-butyne. This analysis of stereoelectronic effects is complemented by the distortion analysis, which provides another clear evidence of selective TS stabilization. Changes in electrostatic potential along the reaction path revealed that azide polarization may create unfavorable electrostatic interactions (i.e., for the 1,5-regioisomer formation from 1-fluoro-2-butyne and methyl azide). This observation suggests that more reactive azides can be designed via manipulation of charge distribution in the azide moiety. Combination of these effects with the other activation strategies should lead to the rational design of robust acyclic and cyclic alkyne reagents for fast and tunable "click chemistry". Further computational and experimental studies confirmed the generality of the above accelerating effects and compared them with the conjugative TS stabilization by π-acceptors.

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Molecular dopants are increasingly studied to enhance the conductivity of semiconducting polymers. Most available p-type dopants have low solubility in common solvents and moderate electron affinities (EA), which makes solution processing difficult and limits the range of semiconducting polymers that can be doped. Here, we describe the synthesis and characterization of the new molecular dopant TMCN3-CP, which has an EA of −5.5 eV. We show that high ionization energy alternating copolymers such as PDPP-4T, PDPP-3T, and PDPP-T-TT-T can be p-type doped and achieve high conductivities with TMCN6-CP using sequential solution processing. The main advantage of this new dopant is the ability to chemically tailor the ester groups, which we demonstrate here for sequential solution doping of films. Sequential solution processing allows a greater ability to control the film morphology and is also desirable for scale-up to large-area polymer electronics. 51 hexylthiophene) (P3HT). 11,12 However, more advanced 52 OSCs tend toward higher ionization energies, 2,13−15 and 53 many cannot therefore be effectively doped with F4TCNQ. 54 This fact has led to a growing interest in dopants with ultralow 55 LUMO energies, and the past decade has seen reports of the 56

High electron affinity (EA) molecules p-type dope low ionization energy (IE) polymers, resulting in an equilibrium doping level based on the energetic driving force (IE-EA), reorganization energy, and dopant concentration. Anion exchange doping (AED) is a process whereby the dopant anion is exchanged with a stable ion from an electrolyte. We show that the AED level can be predicted using an isotherm equilibrium model. The exchange of the dopant anion (FeCl 3 −) for a bis(trifluoromethanesulfonamide) (TFSI −) anion in the polymers poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly[3-(2,2-bithien-5yl)-2,5-bis(2-hexyldecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione-6,5-diyl] (PDPP-2T) highlights two cases in which the process is nonspontaneous and spontaneous, respectively. For P3HT, FeCl 3 provides a high doping level but an unstable counterion, so exchange results in an air stable counterion with a marginal increase in doping. For PDPP-2T, FeCl 3 is a weak dopant, but the exchange of FeCl 3 − for TFSI − is spontaneous, so the doping level increases by >10× with AED.

Generally, the long-range electronic communication between spatially orthogonal orbitals is inefficient and limited to field and inductive effects. In this work, we provide experimental evidence that such communication can be achieved via intramolecular electron transfer between two degenerate and mutually orthogonal frontier molecular orbitals (MOs) at the transition state. Interaction between orthogonal orbitals is amplified when the energy gap between these orbitals approaches zero, or at an "orbital crossing". The crossing between two empty or two fully occupied MOs, which do not lead to stabilization, can be "activated" when one of the empty MOs is populated (i.e., electron injection) or one of the filled MOs is depopulated (i.e., hole injection). In reductive cycloaromatization reactions, such crossings define transition states with energies defined by both the in-plane and out-of-plane π-systems. Herein, we provide experimental evidence for the utility of this concept using orbital crossings in reductive C1-C5 cycloaromatization reactions of enediynes. Communication with remote substituents via orbital crossings greatly enhances regioselectivity of the ring closure step in comparison to the analogous radical cyclizations. We also present photophysical data pertaining to the efficiency of electron injection into the benzannelated enediynes.