Returned Value in Function showing undefined - REST, SharePoint javascript

i'm trying to get the picture details from his user profile in the pictureRetrieve function. when i check the console the PictureDetails value exists for each item . But what i'm trying to achieve is to return the value to the completedetails function.

But the line that calls the pictureRetrieve function runs i get undefined as a result. Not sure if this is a scope problem or return keywords run differently in json.

any help would be much appreciated

function CompleteDetails() {
    var requestUri = _spPageContextInfo.webAbsoluteUrl +"/_api/Web/Lists/getByTitle('OrganisationalChart')/items?$select=Id,user/Title,user/Id,user/Name,Boss/Id,Boss/Title,PictureUrl,Designation&$expand=user,Boss";

    $.ajax({
         url: requestUri,
            type: "GET",
	        async:false,
            headers: { "ACCEPT": "application/json;odata=verbose" },
            success: function (data) {

                var dataResults = data.d.results;

                console.log(dataResults);

            for (var i = 0; i < dataResults.length; i++) {

                var userDetails = dataResults[i]['user'].Name.split('|')[1];
               var employeeId = dataResults[i]['user'].Id.toString();
                var employeeName = dataResults[i]['user'].Title
                var Designation = dataResults[i].Designation != null ? dataResults[i].Designation : '';
               var reportingManager = dataResults[i]['Boss']['Id'] != null ? dataResults[i]['Boss']['Id'] : '';
               reportingManager = reportingManager.toString();

		//Get the user profile picture for each user
                userPicture = pictureRetrieve(userDetails);

            }
        },
        failure: function (r) {
            alert(r.d);
        },
        error: function (r) {
            alert(r.d);
        }
    });
}

var pictureRetrieve = function GetPictureUrl(user) {


            var requestUri = _spPageContextInfo.webAbsoluteUrl +"/_api/SP.UserProfiles.PeopleManager/GetPropertiesFor(accountName=@v)?@v='"+user+"'";

                       $.ajax({

                            url: requestUri,
                            type: "GET",
                            async:false,
                            headers: { "ACCEPT": "application/json;odata=verbose" },
                            success: function (data) {


                               var DataRes = data.d.PictureUrl;
                               var PictureDetails = data.d.PictureUrl != null ? data.d.PictureUrl : 'nouserimageurl';
                                console.log(PictureDetails);
                               return PictureDetails;
                            },
                            failure: function (r) {
                                alert(r.d);
                            },
                            error: function (r) {
                                alert(r.d);
                            }
                       });

}