Extended 7,7,8,8-Tetracyano-p-quinodimethane-Based Acceptors: How Molecular Shape and Packing Impact Electron Accepting Behavior

Abstract

Structural analysis of π-extended 7,7,8,8-tetracyano-p-quinodimethane (TCNQ)-based molecules reveal molecular and packing features which may help better understand the weak electron accepting features for these molecules compared with TCNQ, in solution (cyclic voltammetry measurements), while showing varying trends in thin solid films (photoinduced electron transfer measurements). On the basis of the current findings, we propose that unsymmetrical compounds in this series hold promise as good candidates for use in solar cell applications as their molecular features allow for better solid-state packing, a property likely conducive for better charge transport. Electron acceptor/donor pairs of compatible molecular shapes rather than the usually sought planar shapes may offer a route worth pursuing.

Acenequinocumulenes: Lateral and Vertical π‐Extended Analogues of Tetracyanoquinodimethane (TCNQ)

“…As imilar trend can also be seen when comparing the deviation of the dicyanovinyl groups relative to the central ring of the acene skeleton, namely,t he tilt angles (Table 1): 1a (g 1 = 31.5, 37.98)a nd 1c (g 1 = 34.58)v ersus TCAQ (g 1 = 34.78; g 2 = 34.18), [35] TCTQ (g 1 = 38.88), [50] and 6,13-TCPQ (g 1 = 39.68; g 2 = 39.18). [50] UV/Vis analysis TCPQ derivativesa re typicallyc olorless or yellow,a nd they feature absorptions in the UV or high-energyv isible regions. [51] Dicyanovinylacenequino [3]cumulenes 1a-c and 2,o nt he other hand, are dark red to black solids in the solid state and show brownish-red to dark purple colors in solution.K etoacenequino [3]cumulenes 3a-c and 4 are similarly dark red to black as solids, but are less absorbing in solution, giving bright red colors.…”

“…Because the pendent substituents on the tail of 1a and 1c are distanced from the acene core by the [3]cumulene moiety,t he bending is less that of TCAQ (a = 144.68), [35] TCTQ (a = 135.98), [50] and TCPQ (a = 132.48) [50] as summarized in Ta ble 1. As imilar trend can also be seen when comparing the deviation of the dicyanovinyl groups relative to the central ring of the acene skeleton, namely,t he tilt angles (Table 1): 1a (g 1 = 31.5, 37.98)a nd 1c (g 1 = 34.58)v ersus TCAQ (g 1 = 34.78; g 2 = 34.18), [35] TCTQ (g 1 = 38.88), [50] and 6,13-TCPQ (g 1 = 39.68; g 2 = 39.18). [50] UV/Vis analysis TCPQ derivativesa re typicallyc olorless or yellow,a nd they feature absorptions in the UV or high-energyv isible regions.…”

“…[42] For example, TCTQ and BDCNBA undergo photoinduced electron transfer( PET) almosta se fficiently as fullereneC 60 , [43,44] while TCAQ derivatives have demonstratede ffectiveness in ar ange of PET processes. [50] To date, there are few exTCNQ derivativest hat exceed the lengthof TCTQ, [37,[50][51][52][53] and most derive from the pioneering work of Martin and Hanack,i ncluding 5,14-TCPQ and 6,13-TCPQ, [37,51] and Yamada et al who reported TBPQ. [50] To date, there are few exTCNQ derivativest hat exceed the lengthof TCTQ, [37,[50][51][52][53] and most derive from the pioneering work of Martin and Hanack,i ncluding 5,14-TCPQ and 6,13-TCPQ, [37,51] and Yamada et al who reported TBPQ.…”

“…[45][46][47][48][49] These results are significant, since they emphasize that device efficiency is not solely dictated by acceptor strength, and that shape and/ors olid-state packing of the material are also crucial parameters. [50] To date, there are few exTCNQ derivativest hat exceed the lengthof TCTQ, [37,[50][51][52][53] and most derive from the pioneering work of Martin and Hanack,i ncluding 5,14-TCPQ and 6,13-TCPQ, [37,51] and Yamada et al who reported TBPQ. [52] In these cases,however,the poor solubility in commonorganic solvents restrictsp ractical use, and large HOMO-LUMOg aps limit visible absorptions.…”

“…For example, TCTQ and BDCNBA undergo photoinduced electron transfer (PET) almost as efficiently as fullerene C 60 , while TCAQ derivatives have demonstrated effectiveness in a range of PET processes . These results are significant, since they emphasize that device efficiency is not solely dictated by acceptor strength, and that shape and/or solid‐state packing of the material are also crucial parameters …”