Semiconductor\nPorous Hydrogen-Bonded Organic Frameworks\nBased on Tetrathiafulvalene Derivatives

Abstract

Herein, we report\non the use of tetrathiavulvalene-tetrabenzoic\nacid, H₄TTFTB, to engender semiconductivity in porous hydrogen-bonded\norganic frameworks (HOFs). By tuning the synthetic conditions, three\ndifferent polymorphs have been obtained, denoted <b>MUV-20a</b>, <b>MUV-20b</b>, and <b>MUV-21</b>, all of them presenting\nopen structures (22, 15, and 27%, respectively) and suitable TTF stacking\nfor efficient orbital overlap. Whereas <b>MUV-21</b> collapses\nduring the activation process, <b>MUV-20a</b> and <b>MUV-20b</b> offer high stability evacuation, with a CO₂ sorption\ncapacity of 1.91 and 1.71 mmol g^–1, respectively,\nat 10 °C and 6 bar. Interestingly, both <b>MUV-20a</b> and <b>MUV-20b</b> present a zwitterionic character with a positively\ncharged TTF core and a negatively charged carboxylate group. First-principles\ncalculations predict the emergence of remarkable charge transport\nby means of a through-space hopping mechanism fostered by an efficient\nTTF π–π stacking and the spontaneous formation\nof persistent charge carriers in the form of radical TTF^•+ units. Transport measurements confirm the efficient charge transport\nin zwitterionic <b>MUV-20a</b> and <b>MUV-20b</b> with\nno need for postsynthetic treatment (e.g., electrochemical oxidation\nor doping), demonstrating the semiconductor nature of these HOFs with\nrecord experimental conductivities of 6.07 × 10^–7 (<b>MUV-20a</b>) and 1.35 × 10^–6 S\ncm^–1 (<b>MUV-20b</b>).