Two aryl-fused BODIPY dyes BF-BDP and NF-BDP were synthesized with benzofuran and naphtho [b]furan fusions on the a,bpositions of the BODIPY skeleton, respectively, resulting in large linear conjugated structures. Both molecules were planar and were characterized as intense deep-red/NIR emitters with emission bands tunable by the solution concentration. Their emission bands were red-shifted to l = 730 and 760 nm in vacuum-deposited films.Fluorophores with photoactivity in the deep-red to NIR region (> 650 nm) are of high interest for several applications, such as chemical sensor, [1] bio-imaging label, [2] and organic photovoltaics. [3][4][5] On one hand, however, their relatively low lying emissive excited states allow more possible non-radiative decay routes, which limit the photoluminescent quantum yields (PLQY) of long-wavelength emission. One the other hand, interaction between photons and electrons that is the principle mechanism in all these applications, high stability and low photo-bleaching effect are required. Thus, continuous research efforts have been put into developing and characterizing new deep-red and NIR fluorophores.4,4-Difluoro-4-borata-3a,4a-diaza-s-indacene, abbreviated as BODIPY, is a popular family of dyes characterized by flexible chemical modifications, tunable absorption/emission band, good photo-stability and high fluorescent efficiency. [6,7] Since the typical photo-active region of a BODIPY chromophore is from 450 to 550 nm, several approaches have been realized to achieve deep-red and NIR absorbing/emitting BODIPYs: (1) introduce "push-pull" strategy by introducing electron donating/withdrawing groups; (2) replace meso-carbon atom by a nitrogen atom to obtain aza-BODIPY; (3) extend the p conjugation system by fusing the dipyrromethene core with aryl moieties. [8] Amongst all these methods, aromatic fusion is a promising strategy for the development of high quality emitters, because the extra rigidity provided by the aromatic fusion structure can enhance the thermal/photo-stability and suppress the non-radiative decay routes via the bond vibration and/or rotation. [9][10][11][12] Several recent examples of BODIPY with aromatic fusion along with either a,b-fusion or b-fusion strategy are illustrated in Scheme 1. [13][14][15][16][17][18] Such fused BODIPYs are generally obtained via complex reaction for aryl-fused pyrrole precursors and/or inter-/intra-molecular ring closure, which usually sacrifices the overall yields of the final BODIPYs.
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