A Smart Photochromic Semiconductor: Breaking the Intrinsic Positive Relation Between Conductance and Temperature

Abstract

Breaking the intrinsic rule of semiconductors that conductivity increases with increase of temperature and realizing adramatic dropping of conductivity at high temperature may arouse new intriguing applications,s uch as circuit overload or over-temperature protecting. This goal has now been achieved through T-type electron-transfer photochromism of one organic semiconductor assembled by intermolecular cation···p interactions.C onductivity of the viologen-based model semiconductor (H 2 bipy)(Hox) 2 (H 2 bipy = 4,4'-bipyridin-1,1'-dium;o x= oxalate) increased by 2o rders of magnitude after photoinduced electron transfer (a recordf or photoswitchable organic semiconductors) and generation of radical cation···p interactions,a nd fell by approximately 81 %a t 100 8 8Ct hrough reverse electron transfer and degeneration of the radical cation···p interactions.T he model semiconductor has at least two different electron transfer pathwaysi nt he decoloration process.The development of electronic industry depends largely on the design and synthesis of new semiconductors.For instance, perovskites have brought appealing applications for solar cells, [1] photodetectors, [2] radiation detectors, [3] and X-ray imagers in recent years. [4] Some important applications of semiconductors are strongly related to their intrinsic properties.F or instance,the intrinsic characteristic that conductivity (s)i ncreases with the rise of temperature has been used to fabricate thermistors,w hich are widely used in production, life,medical, research, teaching,and so on. If conductivity has as udden drop at high temperature,i ntriguing applications will be developed. Fore xample,t he corresponding semiconductor can act as ac ircuit protector in the cases such as circuit overload, short circuit, or appearance of an external heat source.This work presents an effective strategy to realize this goal.Photochromic materials can reversibly convert between two stable forms with different electronic and molecular structures, [5] and thus find many appealing applications. [6] If the back reaction can occur thermally,t he phenomenon is called T-type photochromism. [5] As illustrated in Figure 1, if conductivity of one T-type photochromic semiconductor increases after photoconversion from A to B (coloration process), then the heat-induced reverse reaction from B' ' to A' ' (decoloration process) will cause the dropping of conductivity and realize the breaking of intrinsic positive relation between conductance and temperature at high temperature.V iologen (N,N'-disubstituted-bipyridinium) compounds are famous owing to their electron-transfer (ET) photochromic properties.W e [7] and the Roy group [8] recently reported that viologen-based semiconductors could be obtained through infinite stacking of viologen components by cation···p interactions,a nd they showed ar emarkable increase of conductivity after photoinduced electron transfer (PIET) from an electron donor to the viologen p-aggregate and generation of radical cation···p interactions.Decoloration of vi...

Directed self-assembly of viologen-based 2D semiconductors with intrinsic UV–SWIR photoresponse after photo/thermo activation

“…Viologen (N,N′-disubstituted bipyridinium) compounds are good candidates for single-component organic-based semiconductors with broadband photoresponse. Firstly, strong cation···π interactions between viologen components favor the construction of organic semiconductors, and conductance and photoconductance of viologen-based semiconductors may dramatically increase after photoinduced electron transfer (PET) and generation of free radical products [19][20][21] . Secondly, single viologen cation usually has a red-shifted absorption band after forming a radical species.…”

An Ion‐In‐Conjugation‐Boosted Organic Semiconductor Gas Sensor Operating at High Temperature and Immune to Moisture

“…To date, we have investigated the sensory performance of squaraines/squaramides [2, 5, 7] . However, owing to the plane structure and high density of zwitterions, [5] the conductivity of the latter increases significantly with temperature, [8] thereby suppressing the response signals at high temperatures. Croconates, another class of IIC materials that exhibit steric hindrance and hence prevent planar configurations [9] compared with squaraines, are expected to indicate a smaller increase in conductivity with increasing temperature [10] …”

Dynamic Manipulating Space‐Resolved Persistent Luminescence in Core–Shell MOFs Heterostructures via Reversible Photochromism

“…Photochromism, the color change upon light irradiation, has been paid much attention to construct information storage, smart window, and optical sensor. [34][35][36][37][38][39][40][41][42][43][44][45] To date, although photochromic systems have been used to tune the nonlinear optics (NLO), [39,40] conductivity, [41,42] and magnetic properties [43][44][45] in molecular materials, it is still very rare to take advantages of photochromic behavior to regulate RTP properties. This is possibly due to the lack of the effective design method for the combination of photochromism and long-lived photoemission within the same system.…”

“…4,4'-bipyridine (4,4'-bipy) is chosen as the ligand, since it has been used as electron acceptor in photochromism, which is prone to achieve electron transfer and generate bipyridine radicals by combining with suitable electron donors. [39][40][41][42][43][44][45][49][50][51][52][53][54] In addition, the Nheterocycles in bipyridine is beneficial to obtain efficient RTP properties. [1-5, 11-18, 21-26, 30-33] A series of MOFs, M-(HCOO) 2 (4,4'-bipy) (M = Zn, MOF-Zn; Cd, MOF-Cd; Co, MOF-Co; Mn, MOF-Mn), have been synthesized, and MOF-Zn/Cd systems exhibit both obvious photochromic and longlived RTP properties: the MOFs present dynamic and tunable persistent luminescence upon photo-stimulus, which show bright yellow afterglow that gradually disappears after further irradiation.…”

“…Benefitting from the introduction of pyridine unit, [39][40][41][42][43][44][45][49][50][51][52][53][54] MOF-Zn exhibits reversible photochromic behavior. As shown in Figures 2 a and S1, the colorless crystal samples turn into blue upon Xe lamp (300 W) irradiation with the optimized wavelength for the coloration process mainly in the range of 310-330 nm.…”