Novel 5‐(Benzo[b]thiophen‐3‐yl)pyridine‐3‐carbaldehyde (BTPA) Functionalization Framework For Modulating Fullerene Electronics

Abstract

Through ac ycloaddition reaction, fullerene( C 60 )w as derivatized with an ovel organic compound 5-(benzo [b]thiophen-3-yl)pyridine-3-carbaldehyde to form the processable and stable 3-(benzo [b]thiophene-3yl)-5-fullero-1-methylpyrrolidinepyridine (BTFP) compound. BTFP exhibits close similarities to phenyl-C61-butyric-acid-methyl-ester (PCBM)i nt erms of first reduction potentialv alues (À0.62 and À0.61 Vv s. Ag/AgCl, for BTFP and PCBM, respectively)a nd lowest occupied molecular orbital (LUMO) energy level values (3.93 eV in both cases). In chloroform, BTFP exhibits ab athochromic shift in the l max of BTFP (l max, BTFP = 290 nm and l max, PCBM = 260 nm), owing to the graftedb enzo [b]thiophene-3-yl)pyridinem oiety.D espite the similarityi nL UMO (3.93 eV) energy values, BTFP and PCBM differ in their luminescence-quenching ability.T he bathochromic shift in the l max of BTFP (relative to PCMB) is likely to contribute to improved light absorption of as uitable donor for photovoltaic applications.The uniquenesso fc losed-cage, nearly spherical C 60 and related fullerenem olecules has attracted considerable attention. The icosahedrals ymmetry [1] and numerousp ossibilities of functionalizationa llow the modulation of their optoelectronic properties, [2] leading to unabated interest in these intriguing carbon allotropes. The chemistry of fullerenes is that of electron-poor olefins, with sp 2 carbon atoms constrained into apyramidalized geometry.M ultiple double bonds are available on the carbon backbone, making multiple functionalization [3] an interesting route towards new functional materials.This has led to avariety of novel compoundsw ithf inely tunable features thath ave found applicationsa sc atalysts [4] and antioxidants, [5] as well as in sensors [6] and solar cells. [2a, 7] The functionalization of fullerenes does not only modifyt heir properties, but converts them into more processable forms, as pristine C 60 is only sparselys oluble in most solvents, making it intractable. Indeed, the quest for soluble fullerenes was (and still is) one of the main driving forces in the field of covalent modification of carbon nanostructures. Phenyl-C61-butyric-acid-methyl-ester (PCBM), af ullerened erivative, is as olution-processable n-type organic semiconductor,w hich is commonly blended with ptype conjugated polymers to make photovoltaic( PV) cells. However,o wing to the dependence of PV properties on frontier orbital energy levels of donor and acceptors, the application of PCBM to all donorp olymers irrespective of their optoelectronic properties leads to untrue PV properties. For instance,r eports by Susarova et al. [8] and Kästnere tal. [9] compared the PV responses of as et of polymers with PCBM and other functionalized fullerenes and observed that PCBM gave just moderate efficiencies in combination with the polymers, whereas the best PV performances were obtained with ab lend of each polymerw ith specific fullerened erivatives possessing better-suiting molecularstructures. Herein, we describe afulleropyrrolid...