Photochemical & Photobiological Sciences PAPER Cite this: Photochem. Photobiol. Sci., 2018, 17, 835 Received 22nd February 2018, Accepted 15th May 2018 DOI: 10.1039/c8pp00082d rsc.li/pps Modulated photochemical reactivities of O-acetylated (3’,5’-dimethoxyphenyl)heteroaryl acyloin derivatives under direct irradiation and photo-induced electron transfer conditions† Rajesh Bisht, a,c Saumya Singh, b,c Kothandam Krishnamoorthy * b,c and Jayaraj Nithyanandhan * a,c 3’,5’-Dimethoxybenzoin esters are important photoremovable protecting groups which form 2-phenylbenzo- furan derivatives upon photo-release. We utilized a similar concept to test a photochemical method of instal- ling a benzofuran moiety to the conjugated backbone by subjecting O-acetylated (3’,5’-dimethylphenyl) heteroaryl acyloin derivatives through direct photo irradiation and a photo-induced electron transfer reaction. These photochemical methods were explored for a variety of heteroaromatic substrates appended on the ketone part of the O-acetylated cross-acyloin derivatives. The furan, thiophene and bithiophene derivatives led to the expected cyclized (benzofuran capped) products but the derivatives with extended conjugation decomposed under direct irradiation. However, under irradiation in the presence of an electron donor such as triethylamine, the extended acyloin derivatives afforded both cyclized and deacetoxylated products. The semiconducting nature of the extended cyclized products was also explored and tested for solution-pro- cessed organic field effect transistors, providing a maximum hole mobility of 1.3 × 10 -6 cm 2 V -1 s -1 . Introduction Photoremovable protecting groups (PPGs) provide spatial and temporal control over the release of various reactive functional- ities and biologically relevant compounds. 1 The derivatives of 2-nitrobenyl, 2 phenacyl, 3 3′,5′-dimethoxybenzoin, 4 substituted benzyl, 5 coumaryl, 6 and 2-photon absorbing chromophores 7 have been explored as PPGs. Further, the triggers which involve photoinduced electron transfer processes elegantly allow the absorption step to be decoupled from the bond breaking step, which helps to modulate the wavelength of light used in the release process. 8–10 In the case of 3′,5′-dimethoxy- benzoin derivatives, the photo-release event is monitored through the formation of fluorescent 2-phenylbenzofuran, which makes this PPG unique compared to others (Scheme 1). 4,11 Based on the generality of releasing a variety of functionalities, including inorganic phosphates, 12 nucleo- tides, 13 carboxylates, 4,14 and amines, 15,16 3,5-dimethoxyben- zoin derivative based phototriggers have been explored for use in drug delivery, 17 lithographic techniques, 18 biochip fabrica- tion, 19,20 and protein folding. 21,22 It has been established that the excited S 1 (n–π*) 11 and T 1 (n–π*) 23,24 states initiate the removal of functionalities through various intermediates for 3′,5′-dimethoxy and parent benzoin derivatives, respectively. For 3′,5′-dimethoxybenzoin derivatives, intramolecular charge transfer singlet state formation, 11,25 cyclohexadienyl cations, 11,26 carbocations, 27 and biradical intermediates 14,26 have been proposed. In organic electronics, processing the organic molecules plays an important role in achieving the desired morphology for photovoltaic and optoelectronic appli- cations. Methods include the side chain engineering of small molecules/polymers, 28,29 and chemical and photochemical Scheme 1 Photolysis of 3’,5’-dimethoxybenzoin derivatives. † Electronic supplementary information (ESI) available: 1 H, 13 C NMR spectra, absorption/emission spectra for all new compounds, cyclic voltammograms, output and transfer characteristics plots (OFET) and data. See DOI: 10.1039/ c8pp00082d a Physical and Material Chemistry Division, CSIR-National Chemical Laboratory, CSIR-Network of Institutes for Solar Energy, Dr. Homi Bhaba Road, Pune, India 411008. E-mail: j.nithyanandhan@ncl.res.in b Polymer Science Engineering Division, CSIR-National Chemical Laboratory, CSIR-Network of Institutes for Solar Energy, Dr. Homi Bhaba Road, Pune, India 411008. E-mail: k.krishnamoorthy@ncl.res.in c Academy of Scientific and Innovative Research (AcSIR), New Delhi 110025, India This journal is © The Royal Society of Chemistry and Owner Societies 2018 Photochem. Photobiol. Sci. , 2018, 17, 835–845 | 835